ACTA UNIVERSITATIS UPSALIENSIS 7 Studia Linguistica Upsaliensia

ACTA UNIVERSITATIS UPSALIENSIS 7 Studia Linguistica Upsaliensia
ACTA UNIVERSITATIS UPSALIENSIS
Studia Linguistica Upsaliensia
7
Resourceful Language Technology
Festschrift in Honor of Anna Sågvall Hein
Edited by Joakim Nivre, Mats Dahllöf and Beáta Megyesi
Acta Universitatis Upsaliensis.
Studia Linguistica Upsaliensia 7.
214 pp.
c The authors 2008
ISSN 1652-1366
ISBN 978-91-554-7226-9
urn:nbn:se:uu:diva-8933 (http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8933)
Tabula Gratulatoria
Lars Ahrenberg
Ingrid Almqvist
Jens Allwood
Bo Andersson
Jan Anward
Ulla Birgegård
Agneta Emanuelsson Blanck
Kristina Blomqvist
Lars Borin
Sven-Erik Brodd
Rolf Carlson
Sofia Gustafson Capková
Silvie Cinková
Robin Cooper
Mats Dahllöf
Bengt Dahlqvist
Helge J. Jakhelln Dyvik
Susanne Ekeklint
Joakim Enwall
Angela Falk
Danuta Fjellestad
Markus Forsberg
Eva Forsbom
Birgitta Garme
Barbara Gawronska
Christer Geisler
Björn Granström
Maria Toporowska Gronostaj
Britt-Louise Gunnarsson
Ebba Gustavii
Eva Hajičová
Johan Hall
Harald Hammarström
Gerd Haverling
Monica Hedlund
Hans Helander
Johan Heldt
Inga-Lill Holmberg
Merle Horne
David House
Cilla Häggkvist
Bo Isaksson
Carina Jahani
Kerstin Jonasson
Olle Josephson
Päivi Juvonen
Maarit Jänterä-Jareborg
Arne Jönsson
Birsel Karakoç
Fred Karlsson
Marousia Ludwika Korolczyk
Kimmo Koskenniemi
Hans Kronning
Merja Kytö
Einar Lauritzen
Caroline Liberg
Rolf Lundén
Lennart Lönngren
Ingrid Maier
Beáta Megyesi
Ulla Melander Marttala
Gernot Müller
Anette Månsson
Ingela Nilsson
Jens Nilsson
Mattias Nilsson
Joakim Nivre
Elisabeth Wåghäll Nivre
Bengt Nordberg
Torbjørn Nordgård
Coco Norén
Niklas Norén
Mikael Nordenfors
Maria Ohlsson
Leif-Jöran Olsson
Jarmila Panevová
Eva Pettersson
Ulf Pettersson
Helena Pontén
Aarne Ranta
Jan Olof Rosenqvist
Göran Rönnerdal
Markus Saers
6
Filip Salomonsson
Anju Saxena
Marianne Wifstrand Schiebe
Mojgan Seraji
Petr Sgall
Margareta Attius Sohlman
Per Starbäck
Eva Strangert
Ove Strid
Siv Strömquist
Stefan Strömquist
Lars-Göran Sundell
Kerstin Thelander
Mats Thelander
Jörg Tiedemann
Per Weijnitz
Åke Viberg
Gun Widmark
Henrik Williams
Caroline Willners
Martin Volk
Gustav Öquist
Preface
As the first holder of the first chair in computational linguistics in Sweden,
Anna Sågvall Hein has played a central role in the development of computational linguistics and language technology both in Sweden and on the international scene. Besides her valuable contributions to research, which include
work on machine translation, syntactic parsing, grammar checking, word prediction, and corpus linguistics, she has been instrumental in establishing a
national graduate school in language technology as well as an undergraduate
program in language technology at Uppsala University. It is with great pleasure that we present her with this Festschrift to honor her lasting contributions
to the field and to commemorate her retirement from the chair in computational linguistics at Uppsala University. The contributions to the Festschrift
come from Anna’s friends and colleagues around the world and deal with
many of the topics that are dear to her heart. A common theme in many of the
articles, as well as in Anna’s own scientific work, is the design, development
and use of adequate language technology resources, epitomized in the title
Resourceful Language Technology.
Uppsala in May 2008,
The editors
Contents
1
2
3
4
5
6
7
8
9
Lars Ahrenberg
Searching Parallel Treebanks for Translation Relations . . . . . . . . .
11
Lars Borin, Markus Forsberg and Lennart Lönngren
The Hunting of the BLARK – SALDO, a Freely Available
Lexical Database for Swedish Language Technology . . . . . . . . . . .
21
Silvie Cinková, Eva Hajičová, Jarmila Panevová and Petr Sgall
The Tectogrammatics of English: on Some Problematic Issues
from the Viewpoint of the Prague Dependency Treebank . . . . . . . . .
33
Robin Cooper
The Abstract-Concrete Syntax Distinction and Unification in
Multilingual Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
49
Bengt Dahlqvist and Mikael Nordenfors
Using the Text Processing Tool Textin to Examine Developmental
Aspects of School Texts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
61
Eva Forsbom
Good Tag Hunting: Tagability of Granska Tags . . . . . . . . . . . . . . .
77
Kimmo Koskenniemi
How to Build an Open Source Morphological Parser Now . . . . . . .
86
Beáta Megyesi, Bengt Dahlqvist, Eva Pettersson,
Sofia Gustafson-Capková and Joakim Nivre
Supporting Research Environment for Less Explored Languages:
A Case Study of Swedish and Turkish . . . . . . . . . . . . . . . . . . . . . . .
96
Joakim Nivre, Beáta Megyesi, Sofia Gustafson-Capková,
Filip Salomonsson and Bengt Dahlqvist
Cultivating a Swedish Treebank . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
10 Torbjørn Nordgård
Oversettelsesassistenten . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
11 Aarne Ranta
How Predictable is Finnish Morphology? An Experiment in
Lexicon Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
12 Anju Saxena and Mikaëla Lind
Corpora in Grammar Learning – Evaluation of ITG . . . . . . . . . . . . 149
13 Jörg Tiedemann
Prospects and Trends in Data-Driven Machine Translation . . . . . . . 159
14 Åke Viberg
Riding, Driving and Traveling – Swedish Verbs Describing
Motion in a Vehicle in Crosslinguistic Perspective . . . . . . . . . . . . . 173
15 Martin Volk
The Automatic Translation of Film Subtitles – A Machine
Translation Success Story? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202
10
Searching Parallel Treebanks
for Translation Relations
Lars Ahrenberg
Linköping University
Department of Computer and Information Science
1
Introduction
The relation of a translation to its original is of interest both to machine translation research and translation studies. In the latter field most of the work goes
back to the so called linguistic period with Catford (1965), Vinay and Darbelnet (1977), and van Leuven-Zwart (1989) as prominent contributors. After
what has been termed the cultural turn in translation studies, the preoccupation
with translation relations is sometimes described in negative terms, even as a
kind of dead end (e.g., Snell-Hornby, 2006), but especially in text books this
aspect of translation studies is still prominent. Ingo (2007) is a recent example.
There can of course be no denial that target factors such as readership, historical period, perceived or explicit purpose, and cultural function determine
the character of a translation. And so does the translator and her individual
preferences and styles, at least in literary translation. But it is reasonable to
make a distinction between description and explanation. Thus, I take it that
categories such as interlinear (or word-for-word) translation, semantic, communicative, instrumental, and adaptive translations have an objective character
where evidence for the categorization of a translation reside, wholly or partly,
in the relation between source and target texts.
Translation relations primarily serve a descriptive purpose, but an important
one. The characterization of a translation as a whole must be supported by
evidence at the micro-level. This also means that characterization of the translation norms that are dominant for a certain historical period or type of translation rests on micro-level concepts. In addition, translation relations serve a
pedagogical purpose in naming and explicating the possibilities and variants
that are available to a translator. For the machine translator they can be of
great value for evaluation and profiling of systems.
Parallel corpora are prime resources for the study and modelling of translations used in both computational linguistics and translation studies. In parallel
corpora we do not only find alignments at the word level, but today also syntactic annotations and alignments at the phrase level. Thus, the parallel corpus has
11
become a parallel treebank. Neither syntactic annotation nor word alignment
are processes that can be performed automatically with sufficient accuracy for
reference data, which entails that accurate phrase alignment is hard to obtain
without substantial manual efforts. Given that human resources are limited,
one would like to make as much use of the manually reviewed annotations and
alignments as possible.
The design and development of search interfaces to parallel treebanks is a
challenge. A potential problem with any search interface is the mismatch in
conceptualisation and vocabulary between users and developers. In the case
of parallel treebanks, developers tend to be computational linguists, but if the
resource is to be targeted at translators, translation scholars, and even interested
laymen, the problem is real. As long as the interest is with the translation of
words, there is less of a problem, but when attention is focused on structural
and semantic changes the vocabularies and concepts are quite different. There
is a great leap from alignment to notions such as shift or modulation!
There are but two ways to overcome the distance between user and treebank; either the users learn the details of the annotation, or the system offers
search terms that are more easily understood by the users. These are not mutually exclusive, of course. In this paper, however, I will focus on the latter
approach, and look into the question how far a parallel treebank that is accurately annotated and (word) aligned can support queries that are couched in
terms of translation relations. My guess is, though, that descriptions such as
Non-translation of noun or Reordering of head and dependent are easier to use,
at least for the ordinary translator or the language teacher, than an interactive
tool for drawing labelled trees. Part of the solution is then to define a vocabulary and mapping from such descriptions to sets of constraints that can be
applied to the actual data.
If successful, we can reap other benefits as well. As indicated above, it
would allow us to find instances of translation relations without having to find
them manually first. At least, we would be able to scan the search space more
effectively. Assuming that word alignment and syntactic annotation can be performed automatically with sufficiently good performance, we could also hope
to develop programs that categorize translations automatically at the macrolevel with respect to the type of translation, and support its judgement with
profiles at the micro-level. In this paper I will discuss these issues from the
perspective of a specific parallel treebank, the LinES parallel treebank, an outgrowth of research started in the PLUG project (Sågvall Hein, 2002).
2
Translation Relations
The relation of translation to original is manifested at many levels. Here I focus
on the micro-level, i.e., on units smaller than the sentence such as words and
phrases. I will use the term translation relation for a type of correspondence
12
between a micro-level item of a source text and the word or words that we
deem constitute its translation in the target text.
An early attempt at systematizing translation relations is Catford (1965). He
introduced the notion of translation shift to denote “a deviation from formal
correspondence”, where formal correspondence means that a source unit is
translated by a target unit that has the same number of words, and where each
word is equivalent in meaning with its source word. Catford further classified
the shifts as (i) level shifts, and (ii) category shifts. Level shifts are restricted to
shifts between grammar and lexis, while the category shifts are further divided
into (a) rank (or unit) shifts, (b) structure shifts, (c) class shifts, and (d) intrasystem shifts.
Another major contribution is Vinay and Darbelnet (1977) who defined a
number of different types of correspondences: loan, calque, literal translation,
transposition, modulation, equivalence, and adaption. In fact, they argued that
these relations could be identified at three levels of correspondence: the lexical
level, the phrase or grammar level, and the level of the message as a whole. An
interesting aspect with these categories is that they define a kind of distance
scale from target item to source item with identity at the one end and pragmatic
associations at the other end.
van Leuven-Zwart (1989) develops a very detailed taxonomy that combines
two grounds for classification: a formal difference in grammar or lexis, and a
level such as stylistic or syntactic-semantic at which the effect of the change is
located.
Ingo (2007) recognizes four aspects of text that are of constant importance to
translation: the grammatical structure, the semantics, the text varieties, and the
pragmatic aspects. As for the first aspect he uses a fairly elaborate taxonomy
of formal shifts at the clause level in terms of clausal rank (Sw. satsgrad) and
shows that languages differ with respect to their use of different ranks.
3
Word Alignment
In computational linguistics the notion of alignment became prominent with
the increasing interest in parallel corpora in the 1990s. The basic idea is that
units are aligned, whether at the sentence level or at the word level, when they
correspond under translation. While alignment can be given a formally precise
definition, it is notoriously difficult to apply consistently to empirical data and
thus tends to become semantically overloaded. In contrast, the translation relations proposed within translation studies are usually provided with informal
definitions that make intuitive sense.
Word alignment is usually defined as a relation between source tokens (words)
and target tokens. Thinking of translation as the production of a target sentence
from a source sentence Brown et al. (1990) write: “a word is aligned with the
word that it produces”. If a word produces nothing it remains unaligned, and
13
if it produces more than one word it is aligned with all of them. Later works
on statistical machine translation and alignment have used slightly different
definitions, but the important thing to note for the moment is that an alignment
presupposes a specific tokenization of sentences and associate each token of
one tokenization with zero or more tokens from the other. Moreover, alignment is subject to the condition that if two tokens have some token in common
in their alignment, then they must share all tokens that they are aligned to.
This case represents a correspondence that applies to a sequence as a whole,
and which cannot be reduced to several correspondences among the parts.
In developing gold standards for evaluation a distinction between sure and
possible, or clear and fuzzy, alignments is often made. This is a reflection of
the difficulties people have experienced in agreeing on alignment judgements.
It is not, however, a good strategy for alignment in reference corpora, where
categories should reflect properties of the data consistently.
4
Word Alignment in LinES
The Linköping English-Swedish Parallel Treebank (Ahrenberg, 2007b), henceforth LinES for short, is developed with the primary goal of investigating
how common words and grammatical constructions are treated when translated from English into Swedish. It can also be used as a test-bed for various
studies of parallel data.
All tokens in LinES are annotated with information about stem, part-ofspeech, morphological properties, and head token. The head token is given by
a dependency analysis covering the complete segment that the token is part of.
A segment is usually a single sentence, but it can be a phrase, or two or more
sentences in sequence.
Word alignment in LinES is performed semi-automatically using the following major guidelines (see Ahrenberg, 2007a, for details):
• A content word of the source text is aligned with a content word of the
target text iff they are related both structurally and semantically, though
not necessarily synonymous. Multi-word units such as English compounds, and verb-particle constructions, are often aligned to a single
content token on the other side,
• A function word, or functional multi-word unit, of the source text is
aligned with a target function word iff they correspond structurally and
have related functions.
• Words for which corresponding words cannot be found are aligned to a
null element,
• Whenever possible a large alignment, i.e., one where two or more tokens
on one side are aligned with two or more tokens on the other side, should
14
be analysed into smaller alignments. For instance, a phrase such as this
afternoon when translated by i eftermiddag, is aligned using three small
alignments this ∼ 0, afternoon ∼ eftermiddag, and 0 ∼ i.
The reason for preferring small alignments is that the larger alignments will be
created anyway in the phrase construction process.
A word alignment is primarily a relation between sets of tokens. From the
alignment relation we can easily obtain an image function, I, that maps each
source token on a set of tokens from the target sentence. Let s be a source
token and S be the set to which s belongs under the word alignment A. Then
I(s) = T if and only if A(S, T ).
5
Phrase Alignment
In statistical machine translation phrase-based models have come to replace
word-based models. A phrase is then usually taken to be any sequence of
alignments that cover connected parts of both source and target training data.
In LinES, a phrase is defined as a connected sequence of tokens that includes
the head for all tokens that are part of it. To distinguish this entity from other
kinds of phrases, I will refer to it as a headed phrase. This definition is an
attempt to achieve a reasonable balance between recognising too few phrases,
say only complete units, i.e., a head with all its direct or indirect dependents,
or too many phrases, if any connected sequence of tokens is allowed to count
as a phrase.
As an example, consider the nominal syntagm a very nice car. Sub-sequences
of this syntagm that are recognized as headed phrases are very nice, nice car,
and very nice car. The sequence a very, however, is not recognized as a headed
phrase, since both words have their heads outside the sequence.
Some of the headed phrases generated in this way do not usually count as
proper syntactic constituents. For instance, the sequence trees in is a headed
phrase in the sequence the trees in our garden, as prepositions are regularly
analysed as heads of prepositional phrases.
To determine the alignment of a source phrase, the image of every token in
the phrase is determined. Taking the union of all such images we obtain a set
of target tokens that constitutes an image of the phrase. We call this a minimal
image of the phrase. Other images can be constructed, too, as null-aligned target tokens may exist. For instance, consider the the following sentence pair:1
EN: It is my childhood revisited.
SE: Det är som ett besök i barndomen.
The word alignments have been formed as follows: my ∼ 0, childhood ∼
barndomen, revisited ∼ besök, 0 ∼ som, 0 ∼ ett, 0 ∼ i. This means that the
1
From Saul Bellow’s To Jerusalem and back: a personal account. Translation by Caj Lundgren.
15
minimal image of the headed phrase my childhood revisited will be {besök,
barndomen}. By adding null-aligned target tokens to the image of the source
phrase, we can obtain the maximal image som ett besök i barndomen which
in this case is the desired image for the phrase. The basic principle employed
in LinES is to add null-aligned function words, provided their heads can be
found in the minimal image, or they constitute the head to the tokens already
included. This principle works well in this example, as the words ett (a), and
i (in) have the noun besök as head, and som (as) is analysed as the head of
besök. In some cases, further discussed below, added content words may also
be included.
English absolute constructions often correspond to complete clauses in Swedish as in Removing the top lid will ensure... being translated by Om du tar
bort det översta locket ser du till... . In this case we would like to include the
subjunction Om as well as the pronoun du in the image of the phrase Removing
the top lid.
6
Searching Parallel Treebanks
As explained in the introduction, I believe that many users would be helped by
having access to taxonomies of translation relations in their search for data in a
parallel treebank. The relations produced by linguistically oriented translation
scholars could then be taken as a starting point. However, they cannot be used
as given. First, terminology is not uniform, but this problem can be handled
by providing definitions. A more serious problem is that they rely, implicitly
or explicitly, on knowledge that is not in the system. For instance, the system
does not have access to meanings, referents or situations so it would be quite
hard for it to distinguish a modulation (“a change of perspective on a situation”) from an equivalence (“something said with the same effect in the given
situation”) using the categories of Vinay and Darbelnet (1977). Those modulations that involve a systematic formal change, such as the use of a passive
form as the translation of an active form, may be recognized, but they should
then preferrably be described as such.
What we want then is a taxonomy based on formal criteria, but presented in
a vocabulary that makes sense to a user that is not so familiar with the formal
concepts and abbreviations found in the parallel treebank.
6.1
Word-level Mappings
A simple means to classify alignments at the word level is to consider the number of tokens that are part of the alignment, positioning the number of source
tokens before the number of target tokens as in 1-1, or 1-2. The number 0
would then be used for null alignments, of course. An advantage of this kind
of representation is that it can immediately be interpreted as formal constraints
on data to be delivered. On the other hand, this representation does not dif-
16
Descriptive term
Numerical type
Omission
1-0
a) of content word
b) of function word
Addition
0-1
a) of content word
b) of function word
One-to-one translation
1-1
Split
a) adjacent
b) non-adjacent
Fusion
a) adjacent
b) non-adjacent
Grouping
Translation relations
Deletion, Implicitation
Level shift, Economisation
Explicitation, Compensation
Explicitation, Level shift
Loan, Calque, Literal translation,
Class shift, Semantic shift
1-n, n > 1
Decompounding, Depronominalization
Transposition
n-1, n > 1
Compounding, Pronominalization
m-n, m,n > 1
Transposition, Modulation, Equivalence, ...
Table 1: A taxonomy of word alignment types and their relation to some traditional translation relations.
ferentiate between tokens that are adjacent, and tokens that are non-adjacent
when there are two or more tokens in an alignment. Another problem is that it
does not distinguish different kinds of tokens, and in LinES, there is a difference in how function words and content words are aligned. Also, it is quite far
removed from ordinary language, so it should be provided with a terminology,
and that terminology could make up for the other short-comings as well. Table
1 shows a proposal for a taxonomy.
A further analysis could be made on the basis of the annotation, and the syntactic annotation, in particular. This concerns the parts-of-speech, the morphosyntactic properties and the dependency functions. As LinES uses the same
set of values for both English and Swedish, a simple comparison based on
identity of values could be used. This approach is not good enough, though,
and especially with nominal and adjectival inflection, and complex verb forms,
English and Swedish are sufficiently different to warrant a more elaborate approach. The LinES interface allows the user to specify any pair of identical
or contrasting properties in the search interface as constraints on a query. For
example to search for nouns that have been translated by verbs, or plurals corresponding to singulars.
6.2
Phrase-level Mappings
The space of possible phrase level mappings is quite large. Some of the types
of word-level mappings, such as omissions and additions, are found on the
phrase level as well, but other more complex relationships arise. The major
types are the following:
• Dispersal: Adjacent tokens can be aligned with non-adjacent tokens,
17
• Reordering: The order of the images of two tokens may be the reverse
of the order of the tokens themselves,
• Head switch: The head of a token can be aligned with a dependent of
that token, or with a co-dependent token,
• Restructuring: The image of a phrase need not be a phrase.
Note for instance that what is merely an omission or addition when we consider
individual tokens may cause restructuring in the larger context. As an example,
consider the sentence Han behöver träffa en läkare as the translation of He
needs a doctor. The image of needs a doctor will be the non-adjacent words
behöver, en, läkare which is not a phrase of the target sentence. Observing that
the head fills a gap in the string, this is a case where content words arguably
can be added to a phrase, but surely we do not wish to include any addition in
a phrase, even if it is close to it.
The image of a headed phrase under alignment may be related to it formally
in many different ways. Table 2 is not an exhaustive list, but an illustration
of what can be obtained based on implementable criteria. The correspondence
of these types to the translation relations recognized by the tradition is not
always one-to-one. Moreover, the correspondence is less constrained at the
communicative end of the scale. But this is not to be expected as our data does
not give information on the concepts needed at that end, such as perspective or
situation.
A few technical terms will be needed to understand the definitions. We shall
say that a target phrase is equally sized (modulo function words) with a source
phrase iff every content item of the source is aligned with a content item in the
target. Thus, what has happened to the function words is irrelevant; they may
be non-translated, expressed by morphemes, or added. Also, a target phrase is
structurally similar, or C-similar, to a source phrase iff (i) it is equally sized, (ii)
two content items that form a dependency are aligned with two content items
that form a dependency of the same direction, and (iii) the order of content
words is maintained in the translation. Again, the fate of function words in the
translation has no bearing on the concept.
Some of the types in table 2 have a close affinity to translation relations, as is
evident by their names. Other translation relations can be captured fairly well.
For instance, a word-for-word translation with identical source and target parts
is likely to be a loan translation. A literal translation can be defined as a Csimilar translation, or a translation which is C-similar except for the occurrence
of required reorderings. A transposition minimally involves a class shift, while
many modulations can be covered by special combinations of the types listed
in table 2, e.g., the combination of a property shift regarding diathesis with a
subject shift.
18
Descriptive term
Word-for-word
Numerical type Definition
n ∗ (1-1)
C-similar translation where all words have been
translated one-by-one
Omission
n-0
No part of the phrase is translated
Concentration
n-m, n > m
Translation is C-similar with fewer
function words
Dilution
n-m, n < m
Translation is C-similar with added
function words
Reduction
n-m, n > m
At least one content item untranslated
Augmentation
n-m, n < m
At least one content item introduced in
the translation
Downward level shift
n-m, n > m
Function word in source corresponds to
morpheme in target
Upward level shift
n-m, n < m
Function word in target corresponds to
morpheme in source
Required reordering
At least one change in linear order due to
grammatical constraints
Optional reordering
At least one change in linear order not
required by grammatical constraints
Function shift
At least one change in function label
Subject shift
The translation of a subject is not a subject
Property shift
Some content item shows a change in a property
Class shift
C-similar translation with a change in
part-of-speech of the head word
Head shift
n-n
Translation is equally sized but some
dependency has reveresed its direction
Other
Any translation not covered by the defined types
Table 2: A taxonomy of phrase alignment types with definitions.
7
Conclusion
The literature on translation relations provides a rich source of concepts and
terms for describing micro-level phenomena in translations, which have been
little explored in computational linguistics. While some of them apply at the
semantic or pragmatic level, where (current) parallel treebanks contain no relevant data, the structurally oriented ones can be applied for querying parallel
data and sorting results. The taxonomies and definitions proposed in this paper, while tentative and subject to further scrutiny, should be seen as a step in
that direction.
References
Ahrenberg, L. (2007a). Annotation guidelines for the LinES parallel treebank.
URL http://www.ida.liu.se/ lah/transmap/Corpus/guidelines.pdf.
Ahrenberg, L. (2007b). Lines: An english-swedish parallel treebank. In
Proceedings of the 16th Nordic Conference of Computational Linguistics
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(NODALIDA 2007).
Brown, P., J. Cocke, S. D. Pietra, V. J. D. Pietra, F. Jelinek, J. D. Lafferty,
R. L. Mercer, , and P. S. Roossin (1990). A statistical approach to machine
translation. Computational Linguistics 16(2), 79–85.
Catford, J. C. (1965). A Linguistic Theory of Translation: An Essay in Applied
Linguistics. London, Oxford University Press.
Ingo, R. (2007). Konsten att översätta: översättningens praktik och didaktik.
Studentlitteratur.
Sågvall Hein, A. (2002). The PLUG project: parallel corpora in Linköping,
Uppsala and Göteborg. In L. Borin (Ed.), Parallel corpora, parallel worlds,
pp. 61–78. Rodopi.
Snell-Hornby, M. (2006). The Turns of Translation Studies. John Benjamins.
van Leuven-Zwart, K. (1989). The relation of translation to original. Target 1(2), 100–101.
Vinay, J.-P. and J. Darbelnet (1977). Stylistique comparée du français et de
l’anglais. Paris, Didier.
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The Hunting of the BLARK –
SALDO, a Freely Available Lexical Database for
Swedish Language Technology
Lars Borin, Markus Forsberg
Lennart Lönngren
University of Gothenburg
Department of Swedish
University of Tromsø
Department of Russian
For the Snark’s a peculiar creature, that won’t
Be caught in a commonplace way.
Do all that you know, and try all that you don’t:
Not a chance must be wasted to-day!
(Lewis Carroll: The Hunting of the Snark)
1
Introduction
Among Anna Sågvall Hein’s numerous professional interests, computational
morphology and the lexicon were among the very earliest. Her implementation
of a full computational inflectional morphological processor for Russian was
the topic of her PhD thesis (Sågvall, 1973). In the 1980s, she headed the LPS
project1 at the University of Gothenburg. A summary description of her work
in the LPS project, on a computational lexicon for parsing is found in Sågvall
Hein 1988.
Among her most recent research interests, on the other hand, is the creation
of a research infrastructure for Swedish language technology, more specifically
a Swedish BLARK2 (see below).
Against this background, what would be more appropriate than to dedicate
this article about a lexicon component of a Swedish BLARK to Anna?
The need for a basic research infrastructure for Swedish language technology is increasingly recognized by the language technology research community and research funding agencies alike. At the core of such an infrastructure
is the so-called BLARK – Basic LAnguage Resource Kit. A planning project
funded by the Swedish Research Council has been set the tasks of defining
1
A Lexicon-oriented Parser for Swedish.
See, e.g., Anna Sågvall Hein and Eva Forsbom: A Swedish BLARK, presentation at BLARK
workshop, 29th January 2006, GSLT retreat, Gullmarsstrand, Sweden http://stp.lingfil.uu.se/
∼bea/blark/sveblark060129.pdf.
2
21
Swedish BLARK components, surveying the availability and state of the art
of these components, and determining the needs for the immediate future. One
BLARK component identified during this work as lacking at present is a freely
available basic Swedish lexicon with (inflectional) morphological information,
containing at least 50,000 lemmas (Andréasson et al., 2007).
Here we describe our work on creating such a lexical resource, which will
also contain additional useful linguistic information. This resource is SALDO,
or SAL version 2 (see section 2). SALDO currently comprises a semantic
lexicon (described in section 3), a morphological lexicon (discussed in section 4), and a computational morphological description written in FM (Forsberg, 2007), including a full-form lexicon generated with FM (treated in section 5). All components will be released under a Creative Commons AttributeShare Alike license.3
2
SALDO: Background and Scope
Svenskt associationslexikon (SAL; Lönngren, 1992) – ‘The Swedish Associative Thesaurus’ – which formed the basis for SALDO, is a so far relatively
little known Swedish thesaurus with an unusual semantic organization.
SAL was created during the years 1987–1992 by Lennart Lönngren and
his co-workers in the Center for Computational Linguistics at Uppsala University.4 SAL has been published in paper form in two reports, from the Center for
Computational Linguistics (Lönngren, 1998), and the Department of Linguistics (Lönngren, 1992), both at Uppsala University. Additionally, the headwords
and their basic semantic characterizations have been available electronically,
in the form of text files, from the very beginning.
The history of SAL has been documented by Lönngren (1989) and Borin
(2005). Initially, text corpora were used as sources of the vocabulary which
went into SAL, e.g., a Swedish textbook for foreigners and a corpus of popularscientific articles. A small encyclopedia and some other sources provided the
large number (over 3000) of proper nouns found in SAL. Eventually, a list of
the headwords from Svensk ordbok (SO, 1986) was acquired from the NLP and
Lexicology Unit at the University of Gothenburg, and the second paper edition
of SAL (Lönngren, 1992) contained 71,750 entries. At the time of writing,
SALDO contains 72,557 entries, the increased number being due to some new
http://creativecommons.org/licenses/by-sa/3.0/
Gunilla Fredriksson worked together with Lennart Lönngren on the lexeme definitions and
Ágnes Kilár did most of the programming in the original project. Incidentally, the Center for
Computational Linguistics was a research unit created in 1980 on the initiative of Anna Sågvall
Hein who was its director until she accepted the chair in Computational Linguistics at Uppsala
University in 1990 and the Center was merged with the Linguistics Department. Lennart Lönngren – a Slavist by training, like Anna – acted as her replacement for some years while Anna
was acting professor of Natural Language Processing at the University of Gothenburg, which
was when she did a great part of her work on the LPS lexicon.
3
4
22
words having been added, but mainly because a number of entries belong to
more than one part of speech or more than one inflectional pattern.
The work described here first started in late 2003, when Lars Borin and
Lennart Lönngren initiated a collaboration aiming at making SAL available
for online browsing through Språkbanken (the Swedish Language Bank at the
University of Gothenburg). Part of this work consisted in a formal check of
the lexicon, which revealed some circular definitions, that were subsequently
removed. In 2005, a computational linguistics student made a prototype graphical interface to SAL (SLV – Språkbanken Lexicon Visualization; Cabrera,
2005). Using this interface, Lennart Lönngren was able to revise a considerable number of entries with respect to their semantic characterization, so that
SALDO is in this respect no doubt a new edition of SAL, i.e., also as a semantic lexicon.
We soon realized, however, that in order to be really useful in language technology applications, SAL would have to be provided at least with inflectional
morphological information. Thus the work on SALDO began.
3
SALDO: A Semantic Lexicon
As a semantic lexicon, SALDO is a kind of lexical-semantic network, superficially similar to WordNet (Fellbaum, 1998), but quite different from it in the
principles by which it is structured.
The organizational principles of SALDO are quite simple – at least superficially – as there are only two primitive semantic relations, one of which is
obligatory and the other optional. Every entry in SALDO must have a mother
(or main descriptor), a semantically closely related entry which is more central, i.e., semantically less complex, probably more frequent and acquired earlier in first and second language acquisition, etc. The mother will in practice
often be either a hyperonym (superordinate concept) or synonym of the headword (but it need not be either). In order to make SALDO into a single hierarchy, an artificial most central entry, called PRIM, is used as the mother
of 50 semantically unrelated entries at the top of the hierarchy, making all of
SALDO into a single rooted tree.
Some entries have in addition to the mother an optional father (or determinative descriptor), which is sometimes used to differentiate lexemes having
the same mother.
SALDO (or rather: the underlying SAL) is unusual in several respects:
• it contains a number of proper nouns and multi-word units, not normally
found in conventional print or electronic dictionaries;
• it is strictly semantic in its organization; all entries are lexemes – i.e.,
semantic units – and there is no information whatsoever about part of
speech or inflection; homonymous entries representing more than one
23
part of speech are often treated as different, but always because of their
semantics and never for inflectional reasons;5
• the organizational principles of SALDO are different from those of lexicalsemantic networks such as WordNet, in that the semantic relations are
more loosely characterized in SALDO. They also differ from those of
more conventional thesauruses, however, but in this case by having more,
as well as more structured, sense relations among lexemes.
Below, we give a few examples of entries with their mother and father lexemes,
randomly selected under the letter “B” of Lönngren (1992):
balkong : hus (‘balcony’ : ‘house’)
bröd : mat + mjöl (‘bread’ : ‘food’ + ‘flour’)
brödföda : uppehälle (‘daily bread’ : ‘subsistence’)
bröllop : gifta sig (‘wedding’ : ‘get married’)
Bulgakov : författare + rysk (‘Bulgakov’ : ‘author’ + ‘Russian’)
How SALDO is different from typical thesauruses becomes apparent when we
consider that the two primitive lexical-semantic relations (mother and father)
can form the basis of any number of derived relations. Thus the relation ‘sibling
having the same mother (as myself)’ is very interesting, as such sibling groups
tend to correspond to natural semantic groupings.
4
SALDO: A Morphological Lexicon
SAL did not contain any formal information about entries, not even an indication of part of speech. Thus, one important difference between SALDO and
SAL is that SALDO now has full information about the part of speech and
inflectional pattern of each entry.
The morphological description in SALDO was inspired by that of Sågvall
Hein’s LPS lexicon, even if the two descriptions differ in many details. The
main differences are due to slightly different conceptions of what can constitute an inflectional pattern. In our view the inflectional pattern should be
characterized as a set of bundles of morphosyntactic features conventionally
expressed inflectionally in a language. We do not make a distinction between
affixing and other means of morphological exponence. For instance, Swedish
nouns conventionally (maximally) express the following bundles – or combinations – of morphosyntactic features:
singular indefinite nominative
singular definite nominative
singular indefinite genitive
5
For example, the entry alternativ ‘alternative’ is considered to represent only one lexeme,
although in Swedish as in English it has both a noun and an adjective reading.
24
singular definite genitive
plural indefinite nominative
plural definite nominative
plural indefinite genitive
plural definite genitive
There may be subclasses or individual cases of the main parts of speech which
express fewer – or, in rare individual cases, more – such combinations, e.g.,
nouns appearing only in the singular or only in the plural.
In a non-agglutinating language, words will fall into inflectional patterns
according to how the combinations are expressed.6 Such patterns are conventionally known as declensions in nominal parts of speech and conjugations in
verbs.
At the time of writing, with a few hundred multi-word units still to be assigned inflectional patterns and before the final checking of the lexicon, there
are more than one thousand different inflectional patterns represented in the
lexicon. This does not differ radically from what Sågvall Hein (1988) found
when working on the LPS lexicon, although the large number of inflectional
patterns in our description is there partly for different reasons than in her case.
For example, there are no artificial “half-paradigms” in SALDO, due to e.g.,
umlaut plural or ablaut tense formation; these are considered full inflectional
patterns in their own right, just as those expressing the same categories by
suffixation.
Still, there are many singleton inflectional patterns. In many cases, these are
the irregular words of traditional grammar, although there are also subregularities (e.g., among the strong verbs). Surprisingly often, however, the source of
plenty is another, viz. variation. We often find that a particular combination
of morphosyntactic features – a particular cell in a paradigm – for a word or
small group of words can be filled by more than one form, i.e., realized in more
than one way. Such cases are legion, e.g., himmeln, himlen, himmelen ‘heaven
sg def nom’ (citation form himmel), which in all other respects follows the
inflectional pattern designated in SALDO as nn_2u_nyckel, which includes
words like nyckel ‘key’, åker ‘field’, öken ‘desert’, hummer ‘lobster’. This pattern allows only for the first of the three variants shown above for the singular
nominative definite form of himmel, i.e., the form made by affixing an -n to the
citation form.
There is an interesting theoretical issue lurking here. For Wurzel (1989, 57),
an inflectional class (which he uses as a technical term) must have more than
one or even just a few members, although he is not prepared to commit himself
to a specific lower limit. A practically useful computational lexicon should in
any case specify the morphological behavior of individual words as accurately
6
Agglutination is – ideally – the case where each morphosyntactic feature is expressed separately and uniformly, so that there will in principle be no inflectional patterns beyond those
determined by part of speech.
25
as possible. In SALDO, this behavior is encoded uniformly for all words – in
the form of a unique identifier for each inflectional pattern7 – i.e., in the lexicon
we do not make a distinction between inflectional classes and individual cases
in Wurzel’s sense. This task is relegated to the computational morphological
component, where a mapping is made between SALDO’s inflectional patterns
and regular, subregular and idiosyncratic inflectional descriptions. However, it
is not difficult to get a picture of which inflectional patterns are general and
which idiosyncratic. It suffices to extract and count all inflectional pattern designators from SALDO. The following is a list of the inflectional patterns with
more than 1000 members in (the still not final version of) SALDO:
9507
7787
5901
5700
5528
nn_3u_film
nn_2u_stol
av_1_gul
nn_6n_blad
vb_1a_laga
4278
3945
1826
1319
1305
nn_0u_frid
nn_1u_flicka
nn_6u_kikare
nn_0u_tro
nn_5n_ansikte
1216
1084
1046
1018
nn_0n_kaos
ab_i_inte
av_0_korkad
nn_2u_nyckel
These 14 inflectional patterns account for over 50,000 entries or more than
70% of SALDO.
Something which adds to the number of inflectional patterns is that we also
encode some inherent features of words in the inflectional pattern designators,
features which do not bear directly on the inflectional behavior of the word
itself. However, they are potentially useful and comparatively easy to add simultaneously with the morphological information proper, but can be quite difficult to add later, e.g., the gender of nouns, agreement and anaphorical gender
in proper names, etc.
In adding the morphological information to SALDO, we have used existing grammatical descriptions of Swedish inflectional morphology – above
all Svenska Akademiens grammatik (Teleman et al., 1999), but also Hellberg
(1978) – as well as the inflectional information provided in existing Swedish
dictionaries, primarily Nationalencyklopedins ordbok (NEO, 1995; in the form
of the lexical database which was used for producing NEO), but also its predecessor Svensk ordbok (SO, 1986), and Svenska Akademiens ordlista (SAOL,
2006).
For practical and sometimes theoretical reasons we have deviated from these
descriptions (which – we should add at this point – are not always consis7
The identifiers were designed to have some internal structure for the benefit of humans
working with the lexicon. We cannot for resons of space go into any details here – they will be
given in full in the documentation to accompany SALDO – but just to give the reader a flavor
of how identifiers are built up: The identifier nn_3u_film below conveys the information that
this is a third declension (“3”) uter gender (“u”) common noun (“nn”) inflected like the noun
film ‘film’.
26
tent among themselves). For example, we have not found Hellberg’s “technical
stem” a useful concept.8
The inflectional information in SALDO deviates from that found in conventional dictionaries at least on two counts:
1. Our inflectional patterns are quite generous as to which forms are supposed to exist for a lemma. We thus subscribe to the notion of “potential form” which is inherent in the concept of inflectional paradigm, the
general principle being that there should be a clear(ly statable) grammatical, semantic or pragmatic reason for us to postulate the absence of
some form or forms in the paradigm of a lexical item. In practice, this
is often the case with number in nouns, comparison in adjectives and
certain adverbs, and past (passive) participles in verbs. This principle
means that SALDO recognizes fewer uninflected items than traditional
dictionaries (e.g., dna/DNA, which in SALDO also has indeterminate
gender, to boot; both dna:t and dna:n are valid definite forms, according
to SALDO). In general, then, if SALDO differs from modern Swedish
reference dictionaries, SALDO will accept more forms for a lemma. The
only systematic exception to this is that we recognize a class of verbs
that do not form past participles, an inflectional pattern that the dictionaries do not seem to recognize at all.9 Thus, in SALDO, we distinguish
between two second-conjugation verb lemmas väga ‘weigh’, where traditional dictionaries recognize only one verb lemma with two meanings,
only one of which correlates with the ability to form the past participle:
väga vb_2a_leva (i.e., väger, vägde, vägt, vägd)
väga vb_2m_väga (i.e., väger, vägde, vägt, –)
2. A lexicon for language technology must lend itself to the analysis of
arbitrary free text, e.g., on the internet, where we will find many word
forms which are not accepted by normative dictionaries of the written
language, but still recognizeable as possible variant inflected forms of
some existing lemma. Hence, the SALDO morphology recognizes many
attested (but not normative) forms, e.g., the lemma datum with utral gender and corresponding double indefinite plural forms in -ar/-er). We also
recognize some variant spellings which are not in the norm, but not “prototypical” misspellings (although the borderline between the two is far
from sharp). For example, microvågsugn is a quite common spelling for
8
Hellberg himself says that the technical stem is something that he has had to resort to
because of technical shortcomings (Hellberg, 1978, 15f), and which have since then been eliminated.
9
We are still somewhat more conservative in this respect than Sågvall Hein (1988, 285ff),
who distinguishes four classes of (non-phrasal) verbs, according to their ability to form s-forms
and the past participle.
27
mikrovågsugn (prescribed by the orthographic norm). How should we
treat this spelling (67,000 Google hits as opposed to 182,000 for the
‘correct’ spelling, in early December 2007)? In the SALDO morphology it is considered a variant spelling.
SALDO is thus not a normative lexicon, but rather strives to be maximally
descriptive. At the same time the notion of inflectional patterns (inflectional
classes, paradigms) contains a kind of normativity, namely that which is an
irreducible element of linguistics itself, i.e., the formulation of lawlike generalizations about our languages. It is also a recognition of the fact that, however
large a corpus we collect, we will never see all the inflected forms of all the
entries in our lexicon, not even in a morphologically challenged language like
Swedish.10
At the same time we know as language users that some forms of some words
are not only not attested, but actually non-attestable, e.g., the past participle
forms of some verbs, or comparative and superlative forms of (participle-like)
Swedish adjectives in -ad (e.g., långfingrad). The reasons for the lack of some
forms in a paradigm can be various, semantic or formal (the latter seems to be
the case for the adjectives in -ad), but paradigms can also have “holes” in them
for completely idiosyncratic reasons (Hetzron, 1975). In the SALDO morphology, we take this into account to some extent, but we have preferred to err on
the side of generosity in unclear cases, which means that our morphological
description probably overgenerates. If the lexicon is used in language technology applications for analysis, this is not a problem, as long as a potential but
impossible form does not coincide with an actual other form. The problem of
dealing with this if the lexicon is to be used in natural language generation
applications is left for future work.
5
FM for Swedish
Functional Morphology (FM; Forsberg, 2007) is a tool for implementations of
computational morphological descriptions. It uses the typed functional programming language Haskell (Jones, 2003) as the description language and
supports (compound) analysis, synthesis and compilation to a large number of
other formats, including full form lists, XFST (Beesley and Karttunen, 2003)
source code, and GF (Ranta, 2004) source code.
FM has been around for a couple of years now and has been successfully
applied to a number of languages: Urdu (Humayoun, 2006), Arabic (Smrz,
2007), old and modern Swedish, Italian, Spanish (Andersson and Söderberg,
2003), Russian (Bogavac, 2004), Estonian, and Latin.
The starting point of SALDO’s morphological description is the FM implementation of modern Swedish developed by Markus Forsberg and Aarne
10
On the other hand, this is no more to be expected than you would expect at some point to
have seen “all the sentences of the language” as you collect more and more text.
28
Ranta, which consists of an inflection engine covering the closed word classes
and the most frequent paradigms in the open word classes. All in all, the existing implementation covered approximately 80% of the headwords of SALDO,
but only less than a tenth of the inflectional patterns, or paradigms.
The remaining paradigms in SALDO, however, are typically variants of already existing paradigms rather than being fundamentally different.
For example, consider the paradigm of vers, which is ambivalent in being
a second or a third declension noun. It may be implemented as a combination of the inflection functions of second (nn2) and third (nn3) declension,
exemplified in the function nnvvers.
nnvvers :: String -> Noun
nnvvers vers = combine (nn2 vers) (nn3 vers)
Another example is paradigms with one or more additional word forms, such
as the paradigm of kyrka, a first declension noun with the additional compound
form kyrko, as defined in the function nn1kyrka.
nn1kyrka :: String -> Noun
nn1kyrka kyrka =
compvariants [tk 1 kyrka ++ "o"] (nn1 kyrka)
A complete implementation of a paradigm requires two more things, the interface function of the paradigm and the connection of the interface function to a
paradigm identifier (see Forsberg 2007 for details).
The required time to implement a paradigm may vary, but a mean time is
around 15 minutes per paradigm. This is a reasonable effort to spend on productive paradigms, but for the paradigms containing just one member it becomes prohibitively large. One possibility would be to resort to a simple enumeration of the worst-case word forms, i.e., the non-derivable word forms.
However, we still need these paradigms to be productive, not only for aesthetic
reasons, but to be able to treat compounds where these irregular words appear
as the head.
We chose to create worst-case paradigms where word forms are described
as pairs of suffixes and stem operations. A stem operation is a function from a
string to a string, which allows arbitrary computation to be done to the headword before concatenated with the suffix, i.e., we have the same expressiveness
as before.
This is best explained with an example, here with the paradigm of man,
which is one of the more complicated noun paradigms with gemination and
umlaut. The stem operation id leaves the stem intact, ge is a gemination function, and um performs umlaut on the stem vowel. We only give the four nominative word forms (variation enclosed in squared brackets), since the genitive
is derivable.
paradigm "nn_6u_man" ["man"] $
noun_f Utr
29
([(id,"")],
[(ge,"en")],
[(um,""),(id,""), (ge,"ar")],
[(ge.um,"en"), (ge,"arna")])
-----
man
mannen
män, man, mannar
männen, mannarna
The reason why it is considerably faster to implement paradigms with worstcase functions is partly because the whole definition is at a single place, but
also because an implementation of a paradigm is decoupled from the rest of
the implementation, which makes it more of a mechanical task. The drawback
is that the paradigm implementations become less declarative.
The FM implementation of the SALDO morphology is now very close to
complete, and the next step will be to ensure the correctness of the implementation.
All paradigms have example headwords in their definition, and FM can compute the inflection tables of these words. The first step will be to proofread
these tables. The next step will be to run spellcheckers on the full form word
list, which will not only allow us to spot errors in the inflection engine but also
in the annotation.
6
Conclusion
So far, there has not been a freely available full-sized computational lexicon
for Swedish providing inflectional morphological information for all entries.
There are certainly several Swedish computational lexicons in existence, including lexicons with inflectional information, some of them quite large – including Anna Sågvall Hein’s LPS lexicon – but none freely available, which
SALDO will be. In addition, it will put a new kind of thesaurus at the hands of
researchers in Swedish Language Technology, a field pioneered by Anna.
References
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32
The Tectogrammatics of English: on Some
Problematic Issues from the Viewpoint of the
Prague Dependency Treebank
Silvie Cinková
Eva Hajiová
Jarmila Panevová
Petr Sgall
Charles University in Prague
Institute of Formal and Applied Linguistics
1
Introductory Remarks
The present paper is aimed to illustrate how the description of underlying
structures carried out in annotating Czech texts may be used as a basis for
comparison with a more or less parallel description of English. Specific
attention is given to several points in which there are differences between the
two languages that concern not only their surface or outer form, but
(possibly) also their underlying structures, first of all the so-called secondary
predication (section 3.2). In section 4, we discuss the representations of these
constructions in the PDT of Czech as compared with the corresponding
annotation in the scenario of a treebank of English (PEDT), being developed
in Prague as an English counterpart of PDT (indlerová et al., 2007, Bojar et
al., 2007).
2
Tectogrammatics
In the Functional Generative Description (see Sgall et al., 1986, Hajiová et
al., 1998), tectogrammatics is the interface level connecting the system of
language (cf. the notions of langue, linguistic competence, I-language) with
the cognitive layer, which is not directly mirrored by natural languages.
Language is understood as a system of oppositions, with the distinction
between their prototypical (primary) and peripheral (secondary, marked)
members. We assume that the tectogrammatical representations (TRs) of
sentences can be captured as dependency based structures the core of which
is determined by the valency of the verb and of other parts of speech.
Syntactic dependency is handled as a set of relations between head words
and their modifications (arguments and adjuncts). However, there are also
the relations of coordination (conjunction, disjunction and other) and of
apposition, which we understand as relations of a further dimension. Thus,
the TRs are more complex than mere dependency trees.
33
The TRs also reflect the topic-focus articulation (information structure) of
sentences with a scale of communicative dynamism (underlying word order)
and the dichotomy of contextually bound (CB) and non-bound (NB) items,
which belong primarily to the topic and the focus, respectively. The scale is
rendered in the TRs by the left-to-right order of the nodes, although in the
surface the most dynamic item, i.e., focus proper, is indicated by a specific
(falling) pitch.
In a theoretical description of language, the TRs are seen in a direct
relationship to morphemic (surface) structures. This relationship is
complicated by many cases of asymmetry – ambiguity, synonymy,
irregularities, including the differences between communicative dynamism
and surface word order (the latter belonging to the level of morphemics).
The core of a TR is a dependency tree the root of which is the main verb.
Its direct dependents are arguments, i.e., Actor, Objective (Patient),
Addressee, Origin and Effect, and adjuncts (of location and direction, time,
cause, manner, and so on). Actor primarily corresponds to a cognitive
(intentional) Agentive, in other cases to an Experiencer (Bearer) of a state or
process. If the valency frame of a verb contains only a single participant,
then this participant is its Actor, even though (in marked cases) it
corresponds to a cognitive item that primarily is expressed by Objective (see
(1)).
(1)
The book (Actor) appeared.
If the the valency frame of a verb contains just two participants, these are
Actor and Objective, which primarily correspond to Agentive and Objective,
although the Objective may also express a cognitive item that primarily
corresponds to another argument (see (2)).
(2)
The chairman (Actor) addressed the audience (Objective)
If the frame contains more than two items, then it is to be distinguished
whether the “third” of them is Addressee, Origin, or Effect (cf. the
difference between e.g., (3) and (4).
(3)
(4)
Jim (Actor) gave Mary (Addressee) a book (Objective).
Jim (Actor) changed the firm (Objective) from a small shop (Origin)
into a big company (Effect).
In a TR, there are no nodes corresponding to the function words (or to
grammatical morphs). Correlates of these items (especially of prepositions
and function verbs) are present in the TRs only as indices of node labels: the
syntactic functions of the nodes (arguments and adjuncts) are rendered here
as functors, and the values of their morphological categories (tense, number,
and so on) have the forms of grammatemes. Functors and grammatemes can
be understood as indices of lexical items.
34
In annotating texts from the Czech National Corpus in the frame of the
project of the Prague Dependency Treebank (PDT) (Haji et al., 2006), we
work with several specific deviations from theoretically conceived TRs
described above. The most important of these deviations is that the
tectogrammatical tree structures (TGTSs) we work with in PDT differ from
TRs in that they have the form of trees even in cases of coordination; this is
made possible by the coordinating conjunctions being handled as specific
nodes (with a specific index, here the subscript coord, distinguishing
between the coordinated items and an item depending on the coordination
construction as a whole). Thus, the (primary) TGTS of the sentence (5), with
many simplifications, is the tree presented in figure 1:
(5)
Mary and Tom, who are our neighbours, have two children.
Figure 1
More details are presented in a linearized form of the corresponding TR in
(5’); note that (i) every dependent item (or a string of coordinated items) is
embedded in its own pair of parentheses, and the functors are present here as
subscripts of the parenthesis oriented towards the head, and (ii) the left-toright order of the nodes, corresponding to the communicative dynamism,
differs from the surface word order of the numeral two, which is
contextually non-bound and is more dynamic than its head noun. Most of the
grammatemes are left out.
(5’) ((Mary Tom)Conj (Rstr be (Obj neighbour.Plur (App we))))Actor have
(Obj child.Plur (Rstr two))
35
Rstr indicates here a restrictive adjunct, App one of Appurtenance (broader
than possession), the other abbreviations being self-explaining.
Dependency trees are projective, i.e., for every pair of nodes in which a is
a rightside (leftside) daughter of b, every node c that is less (more) dynamic
than a and more (less) dynamic than b depends directly or indirectly on b
(where indirectly refers to the transitive closure of depend). This strong
condition together with similar conditions holding for the relationship
between dependency, coordination and apposition, makes it possible to
represent the TRs in a linearized way, as illustrated by (5‘) above. Projective
trees thus come relatively close to linear strings; they belong to the most
simple kinds of patterning.
3
Selected English Syntactic Constructions for
Comparison
3.1 Introduction
A general assumption common to any postulation of a deep (underlying)
layer of syntactic description is the belief that languages are closer to each
other on that level than in their surface shapes. This idea is very attractive
both from the theoretical aspects as well as from the point of view of
possible applications in the domain of natural language processing: for
example, a level of language description considered to be “common” (at
least in some basic features) to several (even if typologically different)
languages might serve as a kind of a “pivot” language in which the analysis
of the source and the synthesis of the target languages of an automatic
translation system may meet (see Vauquois’ known “triangle” of analysis –
pivot language – synthesis, Vauquois, 1975).
With this idea in mind, it is then interesting (again, both from the
theoretical and the applied points of view) to design an annotation scheme
by means of which parallel text corpora can be annotated in an identical or at
least easily comparable way. It goes without saying, of course, that the
question to which extent a certain annotation scenario designed originally for
one language is transferrable to annotation of texts of another language is
interesting in general, not just for parallel corpora.
It is well known from classical linguistic studies (let us mention here –
from the context of English-Czech contrastive studies – the writings of
Czech anglicists Vilém Mathesius, Josef Vachek and Libue Duková) that
one of the main differences between English and Czech concerns the degree
of condensation of the sentence structure following from the differences in
the repertoire of means of expression in these languages: while in English
this system is richer (including also the forms of gerund) and more
developed (the English nominal forms may express not only verbal voice but
temporal relations as well), in Czech, the more frequent (and sometimes the
36
only possible) means expressing the so called second predication is a
dependent clause (see Duková et al., 1994, p. 542 ff.).
It is no wonder then that in our project, secondary predication has appeared
as one of the most troublesome issues. In the present section, we devote our
attention to one typical nominal form serving for the expression of
secondary predication in English, namely infinitive (section 3.2), and look
for its adequate representation on the tectogrammatical layer of PDT. The
leading idea of our analysis is that we should aim at a representation that
would make it possible to capture synonymous constructions in a unified
way (i.e., to assign to them the same TGTS, both in the same language and
across languages) and to appropriately distinguish different meanings by the
assignment of different TGTSs.
The considerations included in the present section of our contribution
resulted from our work on a project in which the PDT scenario
(characterized above in section 2) was applied to English texts in order to
find out if such a task is feasible and if the results may be used for a build-up
of a machine translation system (or other multilingual systems); see
indlerová et al. (2007) and Bojar et al. (2007). This English counterpart of
PDT (PEDT) comprises approx. 50,000 dependency trees, which have been
obtained by an automatic conversion of the original Penn Treebank II
constituency trees into the PDT-compliant a-layer trees (i.e., trees
representing the surface shape of sentences). These a-layer trees have been
automatically converted into t-layer trees.
3.2 Secondary Predication Expressed by Infinitive
Two classes of constructions are often distinguished: equi-NP deletion and
raising. The distinction between the two classes of verbs was already
mentioned by Chomsky (1965, pp. 22-23) who illustrated it on the examples
(6) and (7):
(6)
(7)
They expected the doctor to examine John.
They persuaded the doctor to examine John.
Referring to Rosenbaum (1967), Stockwell et al. (1973), p. 521ff., discuss
the distinction between expect and require (which is even clearer than
Rosenbaum’s distinction between expect and persuade) and point out that a
test involving passivization may help to distinguish the two classes: while
(8) and (9) with an equi-verb are synonymous (if their information structure
is not considered), (10) and (11) with a raising verb are not:
(8)
(9)
(10)
(11)
They expected the doctor to examine John.
They expected John to be examined by the doctor.
They required the doctor to examine John.
They required John to be examined by the doctor.
37
The authors propose a deep structure indicated by (12) for expect (hate or
prefer) and a deep structure that includes an animate object in addition to a
sentential object for require and persuade (see (13)) while it is not important
that this NP is then rewritten as S)
(12) They – AUX – VP [V(expect) NP (the doctor examine John)]
(13) They – AUX – VP [V(require) – NP (the doctor) –
NP (the doctor examine John)]
Such a treatment of structures with equi verbs implies that there must be a
position in the deep structure which is phonologically null (empty category
PRO) and which is coreferential with one of the complementations of the
equi verb; in our examples above, it is the object in (6). In theoretical
linguistics, this issue is referred to as the relation of control (Chomsky, 1981;
see also a detailed cross-linguistic study by Rika, 1999; for Czech, see
Panevová, 1986).
The different behaviour of verbs in the structures verb plus infinitive is
discussed also in traditional grammars of English. Quirk et al. (2004)
observe a certain gradience in the analysis of three superficially identical
structures, namely N1 V N2 to-V N3 (see their Table 16.64a, p. 1216)
illustrated by sentences (14), (15) and (16) (their A, B, and C, respectively),
each of which conforms to this pattern:
(14)
(15)
(16)
(17)
We like all parents to visit the school.
They expected James to win the race.
We asked the students to attend a lecture.
James was expected to win the race.
The authors claim that there is a strong reason to see a clear distinction
between (14) and (16): in (14) they postulate a structure in which N2
functions as the subject of the infinitival clause while in (16) the N2 should
be analyzed as the object of the main clause. However, according to the
authors, (15) partakes in both these descriptions: from the semantic point of
view, the same analysis as that of (14) would be appropriate; from the
structural viewpoint, the analysis similar to that of (16) is preferable. This is
supported by the fact that N2 may become the subject of the passive sentence
(17). With this analysis, N2 behaves like an object in relation to the verb of
the main clause and like a subject in relation to the infinitival clause. The
authors use the term raised object to characterize this situation and they
support their analysis by several criteria.
38
4 Solutions Proposed
4.1 Subject Raising
In the scenario of PEDT (the Prague English Dependency Treebank), the
distinction between the structures with the so-called raising verbs and
control verbs is preserved. The sentence (18) (see figure 2) is a typical
example for the subject raising construction in English, see also a possibility
of (18a) in English:
(18) John seems to understand everything.
(18a) It seems that John understands everything.
Figure 2
However, its Czech counterpart zdát se is connected with certain constraints:
this verb must be determined by verbo-nominal (or only nominal)
complement, see ex. (19). With verbo-nominal complement it has an
analogical structure to the English example in figure 2, see figure 3. These
constraints, however, eliminate this verb from the “pure” raising
constructions; see also the unacceptability of (20) in Czech:
(19) Jan se zdá (bt) smutn.
Lit. John Refl. he-seems (to-be) sad.
(20) *Jan se zdá rozumt.
Lit. John Refl. he-seems to-understand
In English, the modal and phase verbs are considered as belonging to the
class of subject raising verbs. In the PDT scenario (as well as in the
theoretical framework for it, FGD) most of these verbs are treated as
auxiliaries, and their modal meanings are described by morphological
grammatemes assigned to the autosemantic verb. As for modal verbs, this
39
approach is adopted for PEDT as well (see Cinková et al., 2006, p. 88f.).
This approach is planned for the treatment of phase verbs, too (Jan zaal
pracovat [John started to work], Jan zaínal pracovat [John was going to
start to work]) could be described as multi verbal predicates).
The underlying structure proposed for subject raising constructions in
Czech as well as in English is, however, identical to the control verb
constructions, where ACT (i.e., the first argument of the control verb)
controls Sb (subject) of the infinitive clause (see section 4.3).
Figure 3
4.2 Object Raising
The English verbs used as clear examples of object raising verbs have no
Czech counterparts with infinitive constructions; cf. (21) and figure 4 for
English:
(21) John expects Mary to leave.
40
Figure 4
However, the subclass of verbs displaying this operation, called sometimes
ECM (exceptional case marking), share this behavior with Czech
constructions of accusativus cum infinitivo (AccI in sequel). It concerns the
verbs of perception (see (22a) and figure 5 for English and (22b) and figure
6 for Czech):
(22a) John hears Mary cry/crying.
(22b) Jan slyí Marii plakat.
Figure 5
41
Figure 6
There are two possible ways to reflect the underlying structures of these
sentences. The approach (A) is influenced by the English tradition: The
verbs of perception proper (such as to see, to hear) are understood in English
as two-argument structures; if their second argument is expressed by
secondary predication, the first argument of the secondary predication is
raised up and it receives (“exceptionally“) the Accusative form. The
structure given in figure 5 would yield the surface structure (22a) as well as
the surface structure (22c):
(22c) John hears that Mary cries.
(22d) Jan slyí, e Marie pláe.
However, the synonymy illustrated by (22a) and (22c) does not hold in all
contexts, see (23a), (23b), (23c) and (23d), and also (24a) and (24b):
(23a) Jan slyel, e Carmen zpívá Dagmar Pecková.
Lit. Jan heard that Carmen-Acc sings Dagmar Pecková
(23b) Jan slyel, e Dagmar Pecková zpívá Carmen.
Lit. Jan heard that Dagmar Pecková sings Carmen
(23c) Jan slyel Dagmar Peckovou zpívat Carmen.
Lit. Jan heard Dagmar Pecková to-sing Carmen
(23d) ?Jan slyel Carmen zpívat Dagmar Peckovou.
Lit. Jan heard Carmen-Acc to-sing Dagmar Peckova-Acc
(24a) Jan slyel tu skladbu hrát kapelu Olympic.
Lit. Jan heard the piece-Acc to-play the band Olympic-Acc
(24b) Jan slyel, e/jak tu skladbu hraje kapela Olympic.
Lit. Jan heard that/how the piece-Acc plays the band Olympic-Nom
In the pairs (23a), (23b) vs. (23c), (23d) the difference between the meanings
of the polysemic verb slyet [to hear] is reflected: while in (23a) and (23b)
Jan is either the direct hearer of the singing or he may be only told about the
singing, in (23c) and (23d), if it is possible at all, he must be a direct listener.
42
Moreover, the possible pre-posing of the object of the dependent clause (see
(23a) and (24a) for Czech) has no counterpart in English.
In the approach (B) reflecting the situation in Czech the verbs of
pereception are understood as three-argument structures with the underlying
structure given in figure 6 corresponding to the sentence (22d), which differs
from the underlying structure of ex. (22c) given in figure 5.
Under the approach (A), the formulation of the conditions under which the
secondary predication could be nominalized by an infinitive clause seems to
be very complicated while with the approach (B) the raised object is
understood as a part of a cognitive operation, the result of which is
manifested on the level of underlying structure.
4.3 Control (Equi) Verbs
As for the control verbs, the underlying structure proposed for Czech seems
to be suitable for the PEDT scenario as well, see (25), (26) and figure 7, 8. A
special node with lemma Cor is used for the controllee and an arrow leads
from this node to its controller. The list of the verbs sharing the attribute of
control will be nearly identical for both languages.
(25) John refused to cooperate.
(26) The editor recommended the author to correct the errors immediately.
Figure 7
43
Figure 8
We have concluded that though the notions of raising and control are
assumed not to be theory dependent and therefore applicable in both
scenarios (for PDT as well as for PEDT), the differences between these two
classes are not substantial (and they seem to be overestimated in the
theoretical works).
4.4 Nominal Predicates
Analogical control constructions appear with some adjectives in the position
of the nominal predicates in sentences with copula, see (27), (28) and figure
9 for English:
(27) John is eager to please.
(28) John is eager to be pleased.
Figure 9
44
The corresponding underlying structures for Czech sentences (29a), (30a)
are similar to those for English (29b), (30b):
(29a) Jan je schopen to udlat.
(29b) John is able to do it.
(30a) Jan je ochoten bt okován.
(30b) John is willing to be vaccinated.
However, the list of English adjectives complemented by an infinitive clause
is wider than in Czech. In (31), (32) and figure 10 a control between ACT
and the Sb of infinitive clause could be seen:
(31) She was quick to shut the door.
(32) Bob was reluctant to respond.
Figure 10
4.5 Tough Movement
The object-to-subject raising (sometimes called tough movement) takes
place with some evaluative adjectives in complex predicates, see (33a) and
its transformed version after the raising operation (33b, figure 11). This type
of raising has no counterpart in Czech.
(33a) It is difficult to please John.
(33b) John is difficult to please.
45
Figure 11
4.6 Causative Constructions
Causativity of constructions such as (34) and (35) is expressed by the lexical
meanings of the “semiauxiliaries” to make, to get, to have and by the
secondary predication denoting the caused event filling the position of the
PAT(ient) of the semiauxiliary causative verb.
(34) John made Mary stay.
(35) John had Mary clean the window.
Figure 12
The constructions with the Czech verb nechat [to let] and the analogical
underlying structure (with raised subject-to-object position) correspond to
this type of causativity.
46
5 Conclusions
In our contribution, we have briefly discussed certain issues of secondary
predication in which English differs from Czech with the result that most of
them probably can be handled without differences in underlying structures of
the two languages.
There are, of course, other cases in which the TRs of the two languages
certainly differ. We want only to note here that not all such differences
concern syntactic relations (functors). Thus in the case of such grammatical
categories as definiteness or as tense and verbal aspect the differences can be
captured by distinctions in the repertoires and values of grammatemes
(representing morphological values).
Acknowledgements
This work was funded by GA-CR 405/06/0589, MSM 0021620838, and in
part by the Companions project (www.companions-project.org) sponsored by
the European Commission as part of the Information Society Technologies
(IST) programme under EC grant number IST-FP6-034434.
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48
The Abstract-Concrete Syntax Distinction and
Unification in Multilingual Grammar∗
Robin Cooper
University of Gothenburg
Department of Linguistics
1
Introduction
We will characterize a notion of multilingual grammar based on work conducted in the Grammatical Framework (GF), developed by Aarne Ranta (2004,
2007), Perera and Ranta (2007) and Regulus, developed by Manny Rayner
and others (Rayner, Hockey, and Bouillon, 2006; Santaholma, 2007). We will
suggest a way of constructing multilingual grammars using TTR (type theory
with records, Cooper 2005a, 2005b, in preparation) which combines the GF
and Regulus approaches to multilingual grammar with aspects of unificationbased grammar such as HPSG (Sag et al., 2003).
2
Multilingual Grammar
One approach to multilingual grammar development is the porting of one
grammar to a grammar for another (related) language as discussed in Kim
et al. (2003) and Bender et al. (2005). This approach is useful when you have
a large coverage grammar for one language and want to create a similar large
coverage grammar for another language. The approach we will explore here is
the creation of grammars that are simultaneously grammars for more than one
language from the outset. This is useful when you are concerned with small
coverage grammars for a particular application (for example, speech recognition in a dialogue system) and wish to maintain exactly comparable linguistic
functionality in more than one language. It is this second approach to multilingual grammar that both GF and Regulus are concerned with. In GF the emphasis is on abstract and concrete syntax (several different concrete syntaxes
∗
I would like to thank Anna Sågvall Hein for many years of happy and productive collaboration since I joined the Swedish language technology community in 1995. Her support, help
and plain hard work accompanied by unfailing good cheer have meant a great deal. This work
was supported by Vetenskapsrådet project 2005-4211 (Library-based Grammar Engineering)
and Riksbankens Jubileumsfond project 2008-2010 (Semantic Coordination in Dialogue).
49
corresponding to a single abstract syntax) and the use of resource grammars
to express specific characteristics of particular languages. In Regulus, as described by Santaholma (2007), the emphasis is on grammar sharing and the
use of macros to give abstract representations of grammatical phenomena that
can be realized in different ways in different languages. Here we will concentrate on three important ways in which the GF and Regulus approaches are
similar:
abstract representation use of abstract representations of natural language
which can be shared between different languages to a larger extent than
the concrete or surface representations of the languages and which can
serve to represent meanings
interlingua and transfer provision of facilities for both an interlingual and a
transfer approach to translation
resource grammars abstract representation of grammatical information allowing the concrete or surface form of the language to be specified by
an API-like formalism which can be interpreted in different ways depending on which language’s grammatical resource is being used
I shall illustrate how each of these three aspects are realized in TTR using the
grammar TOY1 from Rayner et al. (2006). I shall first give an intuitive characterization of the general grammar architecture that GF employs and how
this is realized using TTR (section 3). The architecture presents a pretty picture of how languages can be related in the framework using an interlingua
architecture for limited domain multilingual grammars. However, mismatches
between languages arise in even the smallest of domains (such as TOY1) and
I will illustrate some of the simple problems that appear to disturb the picture
even for closely related languages such as English and Swedish (section 4).
In section 5 I will suggest that TTR provides us with reasonably elegant techniques for treating these mismatches without unduly disturbing the elegant
interlingual picture.
3
The GF Multilingual Grammar Architecture
At the core of the GF approach is the relation between abstract and concrete
syntax as illustrated in Fig. 1. Abstract syntax, like Curry’s (1961) tectogrammar, provides a representation of the function argument structure underlying
the natural language expressions presented in concrete syntax, corresponding
to Curry’s phenogrammar, where individual language aspects such as word order and morphology are represented. Thus abstract syntax can be shared by
languages which might have radically different realizations in concrete syntax.
It is for this reason that abstract syntax seems to be a good candidate for an
interlingua in at least restricted domain grammars and, since it is expressed in
50
Figure 1: Abstract and concrete syntax
terms of function argument structure, can also do duty as semantic representation of the particular domain, representing what kinds of objects are available,
what properties they have and what relations may hold between them, i.e.,
ontologies in the sense that this term is employed in work on knowledge representation and exploited in OWL (Web Ontology Language).1 The concrete
syntax is defined compositionally on the abstract syntax. That is, for each object, class of objects, property or relation in the abstract syntax there will be an
expression in the concrete syntax and for each way of applying or constructing
objects in the abstract syntax there will be a corresponding combination rule
of expressions in the concrete syntax. For example, in the domain discussed in
this paper, there is a class called Light and another called Fan and a function SwitchOn which maps objects of these classes to an object which is an
Action. In the concrete syntax the phrases (the) light(s) and (the) fan(s) are
related to the class Light and Fan respectively and the phrase switch on to
the function SwitchOn. The phrase switch on the light is related to the action
which results from applying the function SwitchOn to a particular member
of the class Light.
An important aspect of our particular realization of the GF architecture is
that we exploit the similarity of record types to feature structures. We construct grammars in which information from the abstract and concrete levels
are added together. That is, grammars are defined in terms of structures which
simultaneously represent abstract and concrete syntax in a manner which is
similar to the use of signs in HPSG. This will play an important role in our
strategy for dealing with the kind of mismatches discussed in section 4. Thus,
for example, light in abstract syntax will be:2
1
See for example http://www.w3.org/TR/owl-guide.
Record types are represented as records with the label rectype in the Oz programming
language (http://www.mozart-oz.org). sintype(T a) represents a singleton subtype of the type T whose unique element is a. Dependent types such as light([x]) are
represented in an abbreviated form which is slightly imprecise but more readable than the official form which need not concern us in this paper.
2
51
rectype(cat:sintype(’Cat’ n)
domain:sintype(’RecType’
rectype(o_device:device([x])
o_light:light([x])
o_switchable:switchable([x])
x:’Ind’))
id:sintype(’Id’ ’Light’))
This is a singleton type whose unique element is the record:
rec(cat:n
domain:rectype(o_device:device([x])
o_light:light([x])
o_switchable:switchable([x])
x:’Ind’)
id:’Light’)
Thus the abstract grammar provides category information, the domain type associated with the item and an id which in complex elements will indicate the
construction tree of the item according to the abstract syntax. For complex
items it will also provide information about the item’s daughters in a ‘daughters’ field (corresponding to the daughters-feature in HPSG grammars). In the
implementation we are discussing here we have actually derived the type by
combining two separate resources, one which provides the domain information
and one which provides a way of relating the domain information to syntactic
information, presented below.
rectype(o_device:device([x])
o_light:light([x])
o_switchable:switchable([x])
x:’Ind’)
rectype(cat:sintype(’Cat’ n)
id:sintype(’Id’ ’Light’))
The grammar for concrete syntax imports information from the abstract syntax
and adds to it. Thus according to the grammar for the English concrete syntax
the type associated with light is
rectype(agr:rectype(num:sintype(’Number’ sg))
cat:sintype(’Cat’ n)
domain:sintype(’RecType’
rectype(o_device:device([x])
o_light:light([x])
o_switchable:switchable([x])
x:’Ind’))
id:sintype(’Id’ ’Light’)
phon:sintype(’Phon’ [light]))
52
Here agreement and phonology3 information have been added to the type provided by the abstract syntax. The concrete syntax for Swedish is derived by
adding different information to the same abstract representation:
rectype(agr:rectype(def:sintype(’Definiteness’ yes)
gen:sintype(’Gender’ utr)
num:sintype(’Number’ sg))
cat:sintype(’Cat’ n)
domain:sintype(’RecType’
rectype(o_device:device([x])
o_light:light([x])
o_switchable:switchable([x])
x:’Ind’))
id:sintype(’Id’ ’Light’)
phon:sintype(’Phon’ [lampan]))
This view of an approach to limited domain multilingual grammars in which
the different languages share a common interlingual representation is very attractive for a number of reasons. It appears not to have the central problem that
the interlingual approach to general translation has, that is, that the interlingua
has to make all the distinctions that can be relevant for any language that is
connected to it. Here the problem is not to construct adequate interlingua for
all languages. Rather it is to take a given characterization of a domain and
relate it to different natural languages. The engineering advantage for building multilingual applications is great. We need to make sure that the linguistic
coverage is exactly similar in each language if we are, for example, building a
dialogue system to interact with an MP3 in a car. By ensuring that we cover
the abstract syntax in each language we can be sure that we have exactly corresponding coverage in each of the languages. The work on the domain and
abstract syntax can be carried out by different people and the work on relating
the abstract syntax to the concrete syntax need not be carried out by the designer of the domain representation. In addition the definition of the concrete
syntaxes uses general definitions given in a resource grammar which could be
implemented by a linguist who is only concerned with a general characterization of the language and not with any of the work on specific domains. The
line in the code for the English concrete syntax which defines light is4
Light = {ResGram.light AbsDom.light}.sg
The English resource grammar provides a function ResGram.light5 which
applies to the abstract syntax representation AbsDom.light (on page 4) to
3
We follow the honourable HPSG tradition of using lists of words as phonological representations.
4
This uses the Oz notation {F A} which represents the application of function F to argument A.
5
That is, the value of the variable Light in the Oz module to which the variable ResGram
has been set, i.e., the module containing the resource grammar for English. Similar remarks
hold for AbsDom.light.
53
produce a paradigm for the English noun light. This line of code sets the
variable Light to the entry for singular in that paradigm. The corresponding
line in the Swedish concrete syntax is6
Lampan = {ResGram.lampa AbsDom.light}.sg.def
Here the singular definite entry in the paradigm is chosen.
The approach represented by the GF architecture offers the opportunity for
highly structured modular code and the construction of very high level and
powerful formalisms for manipulating grammars. However, translating between natural languages is a messy business and there are many pitfalls which
appear initially to disturb the pretty picture of a common abstract syntax related to several concrete syntaxes, even if we are only looking at tiny domains.
We shall address some of these problems in section 4.
4
Mismatches between Languages
The coverage of the TOY1 example grammar that is introduced in Rayner et al.
(2006) is represented by:
turn/switch on/off the light(s)/fan(s) (in the kitchen/living-room)
dim the light(s) (in the kitchen/living-room)
is the light/fan (in the kitchen/living-room) (switched) on/off
are the lights/fans (in the kitchen/living-room) (switched) on/off7
The coverage for the corresponding Swedish grammar is represented by:
tänd/släck lampan/lamporna (i köket/vardagsrummet)
light/extinguish light[def]/lights[def] (in kitchen[def]/livingroom[def])
vrid ner lampan/lamporna (i köket/vardagsrummet)
turn down light[def]/lights[def] (in kitchen[def]/livingroom[def])
sätt på/stäng av fläkten/fläktarna (i köket/vardagsrummet)
put on/close off fan[def]/fans[def] (in kitchen[def]/livingroom[def])
är lampan (i köket/vardagsrummet) tänd/släckt
is light[def] (in kitchen[def]/livingroom[def]) lit[sg]/extinguished[sg]
är lamporna (i köket/vardagsrummet) tända/släckta
are lights[def] (in kitchen[def]/livingroom[def]) lit[pl]/extinguished[pl]
är fläkten/fläkterna (i köket/vardagsrummet) på/av
is/are fan[def]/fans[def] (in kitchen[def]/livingroom[def]) on/off
Despite the extremely small size of this coverage it contains a number of challenges to the idea that both languages should be related to the same abstract
syntax. The core of the definition of the abstract syntax (prior to combination with domain information) is given in Fig. 2. We will now detail some
6
Here ResGram is set to the module containing the Swedish resource grammar.
The TTR grammar we are discussing in this paper does not account for the optional occurrences of switched in the third and fourth lines.
7
54
DefArt = {Lex ’DefArt’ det}
Light = {Lex ’Light’ n}
Fan = {Lex ’Fan’ n}
Kitchen = {Lex ’Kitchen’ n}
Livingroom = {Lex ’Livingroom’ n}
In = {Lex ’In’ prep}
SwitchOn = {Lex ’SwitchOn’ v}
SwitchOff = {Lex ’SwitchOff’ v}
On = {Lex ’On’ part}
Off = {Lex ’Off’ part}
Be = {Lex ’Be’ cop}
Dim = {Lex ’Dim’ v}
S_VP = {RuleUnary s_vp s vp}
S_Cop_SmallCl = {RuleBinary s_cop_smallcl s cop smallcl}
SmallCl_NP_Part = {RuleBinary smallcl_np_part smallcl np part}
NP_Det_N = {RuleBinary np_det_n np det n}
N_N_PP = {RuleBinary n_n_pp n n pp}
PP_Prep_NP = {RuleBinary pp_prep_np pp prep np}
VP_V_NP = {RuleBinary vp_v_np vp v np}
Figure 2: Abstract syntax (without domain information)
challenges that arise in the relating both coverages to this abstract syntax.
1. Phrases in concrete syntax can correspond to single items in abstract
syntax. In the abstract syntax there are single verb elements corresponding to the single domain function SwitchOn, SwitchOff and
Dim. However, in English SwitchOn and SwitchOff correspond to
phrases such as switch on and turn off. In Swedish these items correspond sometimes to a single word (tänd or släck) and sometimes to a
phrase (sätt på or stäng av). Dim corresponds to a phrase in Swedish
(vrid ner).
2. Single words in concrete syntax can correspond to complex constructions in abstract syntax. Swedish definite nouns can be used to
form a complete noun-phrase corresponding to a tree of the form [NP
Det N] in the abstract syntax.
3. Single items in abstract syntax are not covered by a single item in
concrete syntax.. SwitchOn and SwitchOff are functions in our
domain characterization which apply to both lights and fans. This corresponds well to the concrete syntax of English where both lights and
fans can be switched (or turned) on and off. This is not so in Swedish,
however. The words tänd and släck are used for turning lights on and
off respectively but cannot be used for fans.8 For fans sätt på and stäng
8
The phrase tänd fläkten is grammatical in the language at large but means set fire to the fan
which is not normally required in smart house applications, for example.
55
av are used, but these phrases are not normally used for lights.9 Similar remarks hold for the Swedish for on and off in sentences like Is the
light/fan on/off?.
4. A single category in abstract syntax has to be split in concrete syntax. The items on and off are classified as particles with category part
in our abstract syntax. When you ask whether the light in the kitchen is
on/off in Swedish it is natural to use the (deverbal) adjectives tänd/släckt
in Swedish. Predicate adjectives need to agree in number and gender
with their subject. If particles in this position were always represented
by adjectives in Swedish, this would not cause a great problem. We
could use the name of the category from the abstract syntax but make the
syntax obey the agreement rules for adjectives specified in the Swedish
resource grammar. Thus Swedish adjectives would just get a rather odd
category name in this particular abstract syntax. However, the matter is
not so simple since when we are asking whether fans are on and off we
do use particles in Swedish (på and av). Particles do not inflect and thus
a grammar that tried to make them agree with their subject would fail.
Thus in the Swedish concrete syntax we need to split the category part
from the abstract syntax, using adj when we are talking about lights
and part when we are talking about fans.
These are the kinds of problems that lead to the use of transfer approaches
to translation in place of interlingual approaches. In the Regulus system described in Rayner et al. (2006), facilities are provided for the development of
both transfer and interlingual multilingual grammars but the approaches cannot be put together in a single grammar. In section 5 I want to suggest that
such a combination is desirable and that the pretty picture provided by the GF
interlingual architecture can be maintained by incorporating certain elements
of transfer into it.
5
Integrating Elements of Transfer into an
Interlingual Architecture
The kind of solution to these problems that I will suggest here is perhaps different from the discussion of transfer in the standard GF literature10 in that I
exploit the fact that in TTR we are constructing grammars by successive refinement, that is, adding information about concrete syntax to the abstract syntax.
Since we are carrying along all the abstract syntax information in the concrete
syntaxes we also have the opportunity to carry out refinements on the abstract
9
The verb sätt på is more possible for lights than stäng av perhaps.
See discussion of the GF transfer language by Björn Bringert on http://www.cs.
chalmers.se/~aarne/GF/doc/transfer.html.
10
56
syntax information which is included in the refined grammar. We will take
each of the challenges of section 4 in turn.
1. Phrases in concrete syntax can correspond to single items in abstract
syntax. We allow for non-compositional compounding of words, e.g.,
in the English concrete syntax we define switch on by
V_Switch_On =
{UResSyn.nonCompositionalCompoundWords
Switch On
{UResSyn.imperativeLex AbsDom.switchOn}}
This provides us with a rule which will combine only the specific items
Switch and On to form a verb with the abstract information from
SwitchOn. The tree will correspond to the syntactic form [V V Part]
but abstract information associated with the mother node will correspond to that associated with a single item in the abstract syntax and
any abstract information associated with the daughters will be disregarded. The function NonCompositionalCompoundWords which
does this is provided in the universal syntax resource module (represented here by UResSyn) where general syntactic resources for the construction of grammars are made available.
2. Single words in concrete syntax can correspond to complex constructions in abstract syntax. We allow for non-branching rules in
concrete syntax to associate abstract information with the mother which
results in the application of an abstract syntax rule to an argument. For
example, the Swedish syntax rule which allows a single noun to be a
noun-phrase in this domain grammar11 is defined by
NP_N = {ResGram.nP_N
{UResAbs.applyRule
AbsDom.nP_Det_N
AbsDom.defArt}}
Recall that what the resource grammar provides are functions which will
apply to abstract information and return a rule that incorporates this abstract information alongside the concrete information about syntax and
morphology. Here the Swedish grammar resource for the rule which
constructs an NP from a single noun is provided with an argument which
is the result of applying an abstract rule for NPs containing a determiner
to an abstract argument representing a definite determiner. This is facilitated by the fact that rules are represented as functions which take
11
Note that there are only definite NPs in this small grammar so we do not have to worry
about issues of definiteness here.
57
one argument at a time, similar to the style of much categorial grammar.
Thus, in much simplified form, a rule corresponding to
NP → Det N
is a function
λx : Det λy : N [NP x y]
which takes an element of type Det and returns a function which will
map an element of type N to an NP-structure. This means that applying
this function to a determiner will give us in effect a rule that constructs
NPs out of nouns, as desired. Notice that this is exploiting the fact that
TTR has functions in addition to record types. Thus we have both functional and unification-like behaviour.
3. Single items in abstract syntax are not covered by a single item in
concrete syntax. In the Swedish concrete syntax the word tänd ‘switch
on (for lights)’ is characterized by
Tänd = {ResGram.tända
{RestrictFunction AbsDom.switchOn
Dom.light}}.imp
Here the Swedish resource grammar function corresponding to tända is
not provided with the abstract information corresponding to SwitchOn
but rather a modification of this. In the abstract syntax SwitchOn corresponds to a function which applies to any device (i.e., both fans and
lights). We restrict this function so that it only applies to lights (as characterized in the domain description, Dom). The operation that carries
out the restriction (represented here as RestrictFunction) is provided by a module which is a universal resource for domain information
definition. Note that this strategy again relies on the fact that we are carrying over abstract syntax information to the concrete syntax grammar
and thus have an opportunity to refine it on the way. Since the domain of
the function is characterized in terms of a record type as is also the domain class Dom.light, restricting the domain of the function involves
applying the operation that corresponds to unification on the function
domain type and Dom.light. Thus we are simultaneously enjoying
the fruits of unification and functional approaches.
4. A single category in abstract syntax has to be split in concrete syntax. The adjective tänd is characterized in the Swedish concrete syntax
by
TändAdj = {ResGram.tänd
{SetCat
58
{Restrict AbsDom.on Dom.light}
adj}}.sg.indef.utr
Here the abstract syntax information builds on that provided by on but
restricted to lights in a similar manner to the previous example. However, in addition here we need to set the category information with the
operation SetCat provided by the universal domain resource module.
This is because the category associated with on in the abstract syntax is
part whereas what we need is adj. This is the only non-monotonic
(or destructive) operation that we have suggested here in that it actually
removes information that was present in abstract syntax before. But, of
course, since we are incorporating the information into our grammar for
concrete syntax we do not need to go back and change the information
presented in the abstract syntax grammar and it is this that is important in
language engineering terms since there may be other concrete syntaxes
for other languages which rely on the abstract syntax grammar having
precisely the form it has.
6
Conclusion
We have suggested a way of preserving the attractive and elegant picture of
the GF interlingual architecture by building in elements of transfer into the
construction of concrete syntaxes. The operations we have suggested appear
to be linguistically quite intuitive corresponding to ways in which we think of
the translation relationships that hold between languages. It should be emphasized, however, that at the time of writing this particular TTR implementation
has not been tested on anything much larger than what is discussed here. We
present this, therefore, as a suggestion for ideas to explore rather than established results. We do, however, think it is suggestive of the potential power of
combining functional, type theoretic techniques with unification-based techniques.
References
Bender, E. M., D. Flickinger, F. Fouvry, and M. Siegel (2005). Shared representation in multilingual grammar engineering. Research on Language and
Computation 3, 131–138.
Cooper, R. (2005a). Austinian truth, attitudes and type theory. Research on
Language and Computation 3, 333–362.
Cooper, R. (2005b). Records and record types in semantic theory. Journal of
Logic and Computation 15(2), 99–112.
59
Cooper, R. (in preparation). Type theory with records and unification-based
grammar. Available from http://www.ling.gu.se/~cooper/
records/ttrhpsg.pdf.
Curry, H. B. (1961). Some logical aspect of grammatical structure. In Structure
of Language and its Mathematical Aspects: Proceedings of the Twelfth Symposium in Applied Mathematics, pp. 56–68. American Mathematical Society.
Kim, R., M. Dalrymple, R. Kaplan, T. King, H. Masuichi, and T. Ohkuma
(2003). Multlingual grammar development via grammar porting. In Proceedings of the Workshop on Ideas and Strategies for Multilingual Grammar
Development, ESSLLI 2003, pp. 49–56.
Perera, N. and A. Ranta (2007). Dialogue system localization with the dialogue
system localization with the GF resource grammar library. In Proceedings
of the ACL Workshop on Grammar-Based Approaches to Spoken Language
Processing (SPEECHGRAM).
Ranta, A. (2004). Grammatical Framework: A type-theoretical grammar formalism. Journal of Functional Programming 14(2), 145–189.
Ranta, A. (2007). Modular grammar engineering in GF. Research on Language and Computation 5(2), 133–158.
Rayner, M., B. A. Hockey, and P. Bouillon (2006). Putting Linguistics into
Speech Recognition: The Regulus Grammar Compiler. CSLI Studies in
Computational Linguistics. Stanford: CSLI Publications.
Sag, I. A., T. Wasow, and E. M. Bender (2003). Syntactic Theory: A Formal
Introduction (2nd ed.). Stanford: CSLI Publications.
Santaholma, M. (2007). Grammar sharing techniques for rule-based multilingual NLP systems. In J. Nivre, H.-J. Kaalep, K. Muischnek, and M. Koit
(Eds.), Proceedings of the 16th Nordic Conference of Computational Linguistics NODALIDA-2007. University of Tartu, Tartu.
60
Using the Text Processing Tool Textin to
Examine Developmental Aspects of
School Texts
Bengt Dahlqvist
Mikael Nordenfors
Uppsala University
Department of Linguistics
and Philology
University of Gothenburg
Department of Swedish
Language
1 Introduction
The purpose with this article is to first make a brief presentation of the
functions in the web based text processing tool Textin 1.2, and then to
illuminate these functions by putting the program to use within a research
project in progress that concerns developmental aspects on texts written by
Swedish pupils during school years 5 to 9.1
The text will begin with a brief description of Textins’ main functions, and
then move on to previous research on school texts where computer linguistic
methods either were used or could have been used if the technology had
been accessible at the time being. The article then continues with a
presentation of the results that Textin delivers, and ends with a discussion on
these findings.
2 Textin as a Tool
Computer analysis of language has a long history starting back in the early
days of computational linguistics. Tools for processing texts have been
developed for linguistic applications per se and also in many application
areas where study of language is conducted. The basics of text and word
analysis include the computation of different kinds of word lists and related
statistics, valuable for the language researcher in his task. Barnbrook (1996)
points out some of the main advantages with using computers for language
analysis; the ease of which one can manipulate, select, sort and format data,
the speed and accuracy and so on. This is of course true even more today,
when the ubiquitousness of texts in electronic readable form is becoming
reality.
Aside the last decade of massive software development for language
engineering purposes, the need for classic, simple analysis tools remain.
1
The Swedish school system contains years 0 to 12 (although the last three years are
optional).
61
Whereas tools such as the well-known WordSmith system (Scott, 2004) are
well established, still a need for quick, web-based tools pertains. This paper
presents such a tool, Textin, in part based on an earlier standalone program
TSSA (Dahlqvist, 1994). Textin offers some core tools, designed to be fast,
for small to medium sized texts for immediate analysis over the Internet by a
web interface.
2.1 Implementation
Textin is written in the programming language PHP, which is specially
suited for web applications. Textin can be used for making basic word
analyses and is able to produce simple word lists of various kinds from texts.
The main window for Textin is shown in figure 1. The text to be analysed is
pasted into the available text area and the analysis is started by clicking the
submit button.
The present version 1.2 of Textin has the following URL:
http://www.lingfil.uu.se/personal/bengt/textin/
The program is protected by a login password, which can be given to users
upon request.
2.2
Language Options
The languages supported by Textin are for the moment Swedish and English.
All text in the interface is given in Swedish, and the pages are displayed in
Latin-1 (8859-1) encoding. A drop-down list on the main window enables
the user to choose between languages.
The choice between Swedish and English affects the sorting of the text
constituents. Word lists processed as Swedish text will order words
containing the Swedish letters ‘å’,’ä’ and ‘ö’ in the proper manner for
Swedish, as well as jointly order words with ‘v’ and ‘w’, in contrast to the
English sorting order.
62
Figure 1: The main interface for Textin, showing a school text to be
analyzed.
2.3 Word Lists and N-grams
Textin allows for the creation of several types of word lists:
• Alphabetically sorted
• Final-alphabetically sorted (i.e., reverse order)
• Frequency sorted (descending order)
As an option, given as a check box on the main window, it is possible to
filter away entries from the found tokens not containing any letters or
numerals, i.e., entries not ordinarily considered constituting a word.
All computed word lists are listed in full, together with sequence and
frequency numbers, on the resulting report page (see figure 2). Tokens in
Textin are defined as strings separated by whitespace, i.e., blanks, tabs and
linefeed, and delimiters such as semicolon, slash, exclamation and question
mark as well as double quotes and parentheses. These delimiters together
with period, comma, single quote and colon are trimmed away from the
strings and cannot alone constitute a token. Words are for efficiency reasons
case normalized, so that they contain only lower case letters.
In addition to the various common word lists, Textin also allows for the
creation of some types of n-grams:
63
• Bigrams
• Trigrams
• Tetragrams
For technical reasons, no non-word filtering can be made on the n-grams.
Further, the n-grams do not make any assumptions about sentence
boundaries, of which Textin has no knowledge.
Figure 2: A frequency ordered word list computed from the text in figure 1.
2.4 Statistics
In addition to the produced word lists themselves, Textin also computes and
reports some basic and relevant statistics for the text analysed. These
statistics include:
• Number of tokens found
• Number of types found
• Mean length of tokens
• Type/token ratio (TTR)
• Word variation index (Ovix)
For n-grams, only the number of total n-grams and the number of unique ngrams in the text are given. Otherwise, for the common word lists, the
64
number of tokens is the total number of words found in the text, while types
stand for the number of unique words. For the word lists, the mean length of
the word tokens, not including the delimiters, is given next. The type/token
ratio will be a number between zero and one, and hints at the word richness
and readability of the text. Ovix (Hultman and Westman, 1977) is an
established measure of word variation, which gives information on the level
of complexity of the text. Note that Ovix cannot be computed, and is not
meaningful, when the number of types and tokens are equal.
2.5 Restrictions
PHP and the server environment impose some restrictions on the text
handling capability for Textin. First, a memory limit is set by the server
which yields a text size of maximum about 150,000 words. The length and
variation in each text to be analyzed determines this number in detail.
The recommendation is to keep the texts below 100,000 words, which
corresponds to the word mass for one to two novels of standard length.
Secondly, a time limit is set. The server utilized allows no execution time to
exceed 60 seconds. This should however not be a grave problem, since the
space limit should make itself known well before the time limit is reached.
3
Previous Research Findings on Writing
Development
A quick overview will now follow concerning research that has mainly or
partially focused two of the quantitative measures Textin can provide:
average word length and OVIX (see figure 2). Textin offers more functions
than merely these two, but when it comes to comparing texts over time,
average word length and OVIX are perhaps the more reliable factors.
Another measure, which traditionally has been used as a sign of
productivity, is total text length. Such a measure is here considered being too
sensitive to the different contexts of production and will therefore not be
used. And while already addressing problems of such it must be mentioned
that the two measures used in the article are far from liberated from issues of
context.
3.1 Average Word Length
One point, made by earlier research, is that a texts quality is connected with
its average word length. An extended word length can be considered a sign
of a more mature language, e.g., the capability of economizing language in
order to make it more packed with information. Björnsson (1968) showed
that words that hold more than 6 letters could be considered being “long
65
words”, and a higher relative frequency of such words would indicate a more
mature vocabulary. In the “LÄSK-project”2 (Grundin 1975) 2500 pupils, 7
to 19 years old, were tested for reading and writing ability in order to gain
knowledge about developmental aspects. The measure average word length
was not calculated in this project, but the project clearly shows that the
frequency of long words does increase over that particular 12 year period
(Grundin 1975, p. 53). This gives at least some initial support to the thought
of using word length as a developmental parameter when characterizing
writing ability.
Hultman and Westman’s Gymnasistsvenska (1977) is a large survey
project that describes different quantitative aspects of text production, with
data from school years 10 to 12 (upper secondary school). One of their
conclusions on word length was that it has a positive connection with higher
grade (Hultman and Westman 1977, p. 78). The word length ranges from
4.83 to 5.52; all together giving these pupils an overall average of 5.07
letters/word. Nyström (2000) shows that texts3 written in the same school
stage, now in years 1996 and 1997, scored an average word length of 4.7.
Nyström also points to the fact that type of text or genre (probably)
correlates with average word length. Genres that are mostly built upon
displaying facts gets an average of 5.26 – thus higher than in
Gymnasistsvenska – and in a more informal text type, as a letter, the average
is as low as 4.29 (Nyström 2000, p. 179). The difference in genre makes it
difficult to speak of any decreasing (or increasing) trend within this stage of
the school period, and Nyström declares that larger surveys are needed in
order to compare results (Nyström 2000, p. 178).
Neither Hultman and Westman nor Nyström covers the earlier year’s
average word length, so others will have to complete the longitudinal
picture. Pettersson (1977, p. 131) states that in between school years 5 to 9
the average word length increases from 4.1 to 4.4. Furthermore, Olevard
(1999 and 2002) shows that the average word length in school year 9 has
decreased over the years between test groups. The findings of that study
shows an average word length of 4.18 in 1987 and 4.17 in 1996, based on
those years national tests.4 Lindell et. al (1978) and the project FRIS5
concludes that the average word length in school year 6 is 4,2 and finally, in
school year 4 it is 4,1: a figure perhaps close to the end of the measurable
scale of development.6
2
”Reading and writing competence and its’ development through the school years”.
(Läs och skrivförmågans utveckling genom skolåren.)
3
Based on Nyströms (2000) entire material, i.e., a material consisting of many
different genres.
4
Olevards’ measures are provided by the above mentioned text processing program
TSSA (Dahlqvist 1994).
5
Fri Skrivning i mellanstadiet. ”Free writing within intermediate levels”.
6
The figures mentioned are of course on a general level and individuals does of
course deviate from these approximates as in Larssons (1984) sample where the
lowest (of the listed) average word length turns out to be 3.66.
66
Putting it altogether, one could say – all reservations taken into account –
that between school years 5 and 12 the development increases from 4,1 to
4,9 on a general basis. Then, there is obviously something with word length
that corresponds to age, specifically between the writing in year 9 and years
10-12. Let us continue with the second aspect on text development: Ovix.
3.2 Ovix7
Another parameter, often referred to as a signal of development, is word
variation. This is possible to measure with either a type/token ratio or Ovix
(“Word variation index” – Hultman 1977 and 1993). Ovix is a measure that
works with a logarithm that enables comparison between texts of different
length. This is important because a text of greater length also contains a lot
more of short, logical words, like conjunctions, which reduces the type/token
ratio, thus making it difficult to use when comparing variation as
achievement.
The first project to use Ovix was Hultman and Westman (1977). The total
score in the 1977 material of Hultman and Westman showed that essays with
the lowest grade held an Ovix of 58,7 8 and those with the highest grades had
67.6. As comparison, brochures [61], newspaper text [67.6] and text books
[71] were listed. It was then possible to say that the writers in the upper scale
of grades were closing in on, and overlapped some of the adult texts word
variation. Hultman and Westman also displays a listing of essays with
approximately the same amount of types ranging from an Ovix of 56.7 up to
72.9 – thus a quite striking difference between texts of the same length
making it, on an individual level, impossible to say that only text length can
guarantee text quality within school writing.9
Nyström (2000) uses the same measurement for word variation10 and lists
the values in relation to what educational program in upper secondary school
the pupil attends. Nyström presents Ovix related to two different text types
which are labelled A and B (both written within the national testing system),
where A is a text that is rich of quotations – making the Ovix automatically
higher when quoting more mature writers – and B that is closer to the pupils’
own production and less “importing”. Text type A renders an average of 64
and text type B, 60. The highest Ovix is performed on “theoretical”
programs of the social and natural sciences [68], and the lowest on the more
“practical, profession preparing” programs [48] (Nyström 2000, p. 176).
7
The formula for Ovix 1 is defined with the help of the natural logarithm: ln.Ovix =
1/(ln(2-(ln(types)/ln(tokens)))/ln(tokens)).
8
It is not easy to pin down what one point of Ovix means but the general meaning is
that a higher value signals a better text.
9
In Larssons (1984) sample the correlation between text length and grade is from
0.81 to 0.83, and in Hultman and Westmans 0.57. On an average basis then, longer
texts gets higher grades. The correlation between word variation and grade has been
showed to be: 0.61 (Hultman and Westman, 1977:56).
10
Also extracted through TSSA (Dahlqvist 1994).
67
Another interesting result from Nyström, is the focus on Ovix within
different genres. Ovix, in those texts that holds a large amount of facts and
quotations, like for instance the traditional school report on a specific subject
matter gets 66 on an average basis. Narratives [58] and letters [52] render
lower values, thus the same phenomenon as with average word length.
Turning to the pupils in earlier school stages, Pettersson (1977), shows a
rather depressing curve stating that Ovix stagnates between school year 6
and 9 at the level of 55. This is supported by Sjödoff (1989) that notes a
minor increase in Ovix between school years 7 to 9 – from 47.6 to 51.1 but
the final figure for school year 9 is even lower than it was in Petterssons
sample.11 There is perhaps not enough support from earlier research to
display the word variation on a longitudinal basis, but we can at least state
that it increases from year 4 with an average Ovix of 51 to 63.2 in school
year 12.
4 Putting Textin to Work
4.1 Concerning Method
As mentioned above, programs like TSSA and the lightweight web version
Textin, has successfully been used in order to produce quantitative measures
on text quality. Some measures have proven to have strong connections with
the teachers’ assessment. It has therefore been argued that the two measures
can be considered a) two signals of what defines longitudinal development
and b) signals that in a general way can differentiate achievement within a
small or large sample of pupils. These two arguments constitute a strong
reason for redoing research in a new, longitudinal project. Another
motivation for doing the calculations is to establish bonds between research
projects over time on such a complex subject matter as written texts. It is
thus necessary to reuse some of the methods of analyses used in the
preceding field of research in order to establish a context to the more recent
text material.
4.2 The Project12 and Its Empirical Data
The project has a corpus of texts that originates from 31 pupils attending
school years 5 to 9. The text types are of 12 different kinds, all together 331
texts containing approximately 500,000 words. It is quite a large material but
this is where Textin has its’ advantages. The program is both easily
11
There is also a third result, concerning Ovix on the period school year 6-9, that
states an increase from 55 to 60 (Josephson and Melin 1990:45).
12
The project’s working name is Developmental Aspects on Texts Written in School
Years 5 to 9 Within the Subject Matter of Swedish. From now on, in this article; let
us just call it The Project.
68
accessible through the web and it is also a program that works very fast with
text masses of this particular size. The material as a whole can not be run
through Textin due to the restrictions mentioned above, but the text types
taken separately contains about 70,000 words which is processed in
approximately 3 seconds with Textin. In the following sections the results on
the texts in The Project will be presented and when possible related to earlier
research.
In order to make the results more comparable, the texts from The Project
will be divided into “narratives” and “other texts”. The results on the
national tests will also be compared to 30 texts from the online corpus
Skrivbanken.13 This gives us the (unique?) possibility to compare measures
on national tests performed in school year 9 for the years 1987 and 1996
(Olevard 1999); 1992 and 2003 (Skrivbanken) and 2007 (The Projects 31
tests). We will also display the national model texts’ (texts put forward by
the national tests group, to aid teachers in their grading)14 measures in order
to visualize one demand on text quality on a national level. It is important to
notice that the national test is constructed as a multiple choice of tasks, but a
majority of the pupils gets pulled down by the so to speak “Bermuda triangle
of narratives”. The texts from Skrivbanken are all of a narrative kind.
Within the group of narratives we will also focus upon differences
between the national tests’ text products, and the texts written in a scaffolded
writing environment. It is of course a hypothesis that the results on the latter
texts become different, due to the helpful surroundings. We will return to
this issue to see if any results could support such a hypothesis, and what the
complications for pedagogy and testing system in such case might be. The
texts mentioned as “other” will, in the present article, mainly serve as means
of comparison to the narratives.
4.3 The Project’s Results
4.3.1 Average Word Length in National Tests in School Year 9, Period
1987–2007
Is there something to learn from drawing a longitudinal line through the 20
years of national test results that are accessible to us? The test system has
during this period been more or less thoroughly reformed, and the somewhat
elusive variable context is always around to remind us that it affects the
writing in different ways. Those reservations set aside we can sketch a curve
in figure 3.
13
www.skrivbanken.se. Acknowledgements to Växjö universitet, Daniel Bergman
and Jan Einarsson, for making this material available!
14
For the year 2007 at this adress:
http://www.nordiska.uu.se/natprov/skolar9/exempel9
69
Average Word Length in National Tests and Model Texts
5
4,9
4,8
Letters/Word
4,6
4,56
4,4
4,3
4,2
4,3
4,18
4,2
4,17
4,11
4
3,8
3,6
1
2
3
4
5
6
7
8
Texttype 1-7
Figure 3: Average word length in national tests school year 9 and national model
texts. Texttypes are: 1 – 1986 (Olevard 1999); 2 – 1992 (Skrivbanken.se); 3 – model
texts 1992 (Skrivbanken.se); 4 – 1996 (Olevard 1999); 5 – 2003 (Skrivbanken.se); 6
– 2007 – (The Project’s texts); 7 – Modeltext 2007 (see footnote no., 14) and finally
8, for comparison between different text types, the scientific essay from 2007.
Two main conclusions can be drawn from this curve. First it is possible to
say that the capability measured up with average word length is revolving
quite stable somewhere around 4.2. There should then not be any risk that
the writing competency has decreased. Second, there are two values that are
a lot higher than the rest; the value for the national model text type (2007)
and the scientific essay.
We have already commented upon the fact that a text type like the essay,
which heavily relies on an externally imported lexicon and/or quotations,
must gain a higher average word length. It goes without saying that a text
using the specifying lexicon of e.g., aerodynamics automatically increases in
both maturity and complexity. What about the value on the national model
text then? The three model texts used in this article are the ones that are
accessible online, texts within task C4 which is much more less of a
narrative than the text type that most pupils chose, task C3. On a national
level only 4% chose the text type used as example for the model texts here,
but a total of 66% chose a more pure narrative task (Skolverket 2008), and
so did the Text Projects pupils. Thus, it is not at all strange that our model
text of 2007 gains such a different score; again an evidence of differences
between text types when it comes to measurements of this kind.
70
Average Word Length in Strongly Scaffolded Text
Types and in National Test Situations
4,5
Letters/Word
4,4
4,4
4,3
4,3
4,2
4,1
4,2
4
4,3
4,3
4,2
4,2
4
3,9
3,8
1
2
3
4
5
6
7
8
Text Type 1-8
Figure 4: Average word length in different narrative text types within The Project.
Text types are: 1 – National test school year 5; 2 – Fairy Tale school year 6; 3 –
Teen age short story, year 7; 4 – Criminal short story, year 8; 5 – Robinsonade, year
9; 6 – Horror short story, year 9; 7 – rewriting the national test of school year 5, year
9 and finally, 8 – National test school year 9.
4.3.2
The Projects Narratives Versus the National Tests
Let us now make a comparison between the texts written in the scaffolded
text productions in The Project, and the ones written within the national
tests. We will start by displaying the differences in figure 4. We will also
provide the value for average word length in the national test of school year
5.
This longitudinal curve, based on the same individuals’ achievements over
5 years of school writing, shows a positive progression all the way until texts
7 and 8. The trend after that seems to be a downward bound curve, making
the national test equal to the writing of the year 6 fairy tale. The texts 7–8
are texts written within situations where writing should be performed by
hand during time pressure. In the other text situations, the pupils’ text is
developed during a long period of time with scaffolds like peer response and
word processing present. It is not surprising that there is a difference; it
would in fact be a lot more surprising if it was the other way around!
4.3.3
Ovix Within National Tests, 1992 to 2007
When it comes to Ovix there are no data accessible for some of the years
listed under average word length. For instance, Olevard (1999), does not
provide Ovix measures at all, which gives a curve that is some what weaker
substantiated (figure 5).
71
Ovix in National Tests 1992 to 2007
62
60
60
Ovix
58
56,8
56,1
56
59,5
54
53,8
52,8
52
50
48
1
2
3
4
5
6
Text Situation 1-6
Figure 5: Ovix in national tests and national model texts. Texttypes are: 1- 1992
(Skrivbanken.se); 2 – 2003 (Skrivbanken.se); 3 – model texts 1992
(Skrivbanken.se); 4 – 2007 (The Project’s texts); 5 – Modeltext 2007 (see footnote
no., 14) and finally 6, again for comparison between different text types, the
scientific essay from 2007.
The results are essentially similar to the ones accounted for under average
word length. The national tests Ovix is approximately the same at the years
1992 and 2007. The year 2003 is 3 points lower and this would have to be
looked into in a more extended way. Again, the model texts of 2007 are at a
completely different level compared with the texts of the previous years. Not
even the scientific essay, with its’ importing language style, can outscore the
chosen model text.
Ovix in Different Narratives
70
60
51,2
Ovix
50
49,7
59,8
58,5
56,4
55,6
52,5
56,8
40
30
20
10
0
1
2
3
4
5
6
7
8
Text Type 1-8
Figure 6: Ovix in Different Narrative Text Types Within The Project. Text Types
are: 1 – National test school year 5; 2 – Fairy Tale school year 6; 3 – Teen age short
story, year 7; 4 – Criminal short story, year 8; 5 – Robinsonade, year 9; 6 – Horror
short story, year 9; 7 – rewriting the national test of school year 5, year 9 and finally,
8 – National test school year 9.
72
4.3.4
The Project’s Narratives, versus the National Tests’ Ovix
Figure 6 shows the tendency within narratives of different kinds over the 5
years. The curve is quite similar to the one displayed under average word
length. There is a stable increase in Ovix from the narrative text type Fairy
Tale to Horror Story, and then there is a decrease on the national test. It is
interesting to note that text 7, rewriting the national test from year 5,
receives such an increase in Ovix but a decrease in average word length.
This is merely one of the “asymmetries” that has to be more consequently
looked into by a more qualitative analyses on The Project’s material.
Finally, in this curve, we can not see that the national test is equal to the
writing of the year 6 fairy tale.
5 Discussion
The results based on the material available in this article point to mainly
three facts; first, and this is of course a “metafact” aiding the latter two,
Textin turns out to be a effective tool when it comes to processing texts of
the size of The Project’s. Second; the results on national writing tests
maintain a rather stable level of achievement and third; the measures
displayed here shows that pupils, during school years 5 to 9, do develop
towards a more mature language, although more visible in the scaffolded
text types.
Furthermore, the article points out a sort of inconsequence between the
text processes surrounding the national tests, and the ones dominating the
class rooms visited within The Project. This gives an opportunity to raise the
question of what exactly the purposes could be with these two different
processes. We can either put it this way: The texts produced within the
strongly scaffolded writing processes are not a fair and equal material to use
for individual grading of pupils. One could say that the texts are more of a
social and collective product, than an individual and stand alone
achievement of one writer. Or, we could put it this way: The national tests
are said to be guide lines to teachers who are going to grade pupils in order
to make it possible to make a differentiation before sending them further up
in the educational system. Then why is the national tests’ writing process
conducted in such a manner that it renders poorer results (seen to these
measures)? Why is it conducted in such a different and with the writing
process’ ideal colliding way? As the tests are not said to have the absolute
and statutory function to regulate the pupils final grades, their purpose is
somewhat unclear and this will definitely lead to that they are used in
different ways across the nation. And this is of course something that,
without doubt, causes inequalities and variation between different
classrooms when it comes to what the individual grades really are based on.
73
It seems as if the national level of testing and evaluating writing skills, and
the locally chosen method for teaching and learning writing, is on a collision
course which must cause confusion to the grading teachers involved, at least
to those with less experience?
6 Conclusion
The main conclusions of this article are that Textin works very effectively
thanks to its accessibility via the Web and when working with text masses of
The Project’ssize. It has also proven to be able to build bridges between
research on language development within school contexts of different kinds
over different periods of time. The results from Textin have of course to be
viewed alongside with qualitative approaches to textual analysis to help shed
light on problems like: What words do the variation consist of? What makes
a text of one type so much stronger than another? How come the connection
to grade is so strong? What factors dwells within the teachers’ habitus and
what lies embedded in the school environments’ hidden norms of value?
One final reflection will have to cover all other things concerning writing
and texts; there is of course an abundance of more matters to tend to when it
comes to text quality than merely numbers, but these numbers can serve as a
generator of hypothesises to be investigated by qualitative approaches, and
vice versa. There is nothing to do but to agree with Nyström’s (2000)
conclusion that more large scale surveys are needed and on a regular basis to
further investigate and evaluate the quantitative aspects on achievement
within writing development.
References
Barnbrook, G. (1996). Language and Computer. A Practical Introduction to
the Computer Analysis of Language. Edinburgh, UK: Edinburgh
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Björnsson C. H. (1968). Läsbarhet. Stockholm.
Dahlqvist, B. (1994). TSSA 2.0, A PC Program for Text Segmentation and
Sorting. Uppsala: Institutionen för lingvistik, Uppsala universitet.
Grundin, H. (1975). Läs- och skrivförmågans utveckling genom skolåren.
Utbildningsforskning rapport 20. Stockholm Liber/Skolöverstyrelsen.
Hultman, T. G. and M. Westman (1977). Gymnasistsvenska. Lund, Liber.
74
Hultman, T. G. (1994). Hur gick det med OVIX? I Språkbruk, grammatik
och språkförändring. En festskrift till Ulf Teleman. 13.1.1994. Lund. S.
55-64.
Josephson, O. and L. Melin (1990). Elevtext. Analyser av skoluppsatser från
åk 1 till åk 9. Lund, studentlitteratur.
Larsson, K. (1984). Skrivförmåga. Studier i svenskt elevspråk. Uppsala,
Liber.
Lindell, E., B. Lundquist, A. Martinsson, B. Nordlund B., and I. Petterson
(1978). Om fri skrivning i skolan. Utbildningsforskning FoU rapport 32.
Stockholm Liber/Skolöverstyrelsen.
Nyström, C. (2000). Gymnasisters skrivande. En studie av genre,
textstruktur och sammanhang. Skrifter utgivna av Institutionen för
nordiska språk vid Uppsala universitet, 51. Uppsala, Textgruppen i
Uppsala AB.
Olevard, H. (1999). Tonårsliv. En pilotstudie av 60 elevtexter från
standardproven för skolor (sic) 9 åren 1987 och 1996. I FUMS rapport nr
194. Uppsala FUMS.
Olevard, H. (2002). Skrivuppgift i repris – presentation av ett
forskningsprojekt. I Garme (red. 2002). Språk på väg. Om elevers språk
och skolans möjligheter. Uppsala, Hallgren & Fallgren studieförlag AB.
Pettersson, Å. (1977). Barnspråk. I Pettersson/Badersten (1977) Språk i
utveckling. Lund, Liber läromedel.
Scott, M. (2004). WordSmith Tools version 4. Oxford University Press,
Oxford, England.
Sjödoff, I. (1989). Med svenska som mål. Effekter av två
undervisningsprogram på invandrarelevers svenska i skrift. Skrifter
utgivna av institutionen för nordiska språk vid Uppsala universitet 23.
Uppsala, institutionen för nordiska språk.
Skolverket (2008). Ämnesprovet 2007 i grundskolans årskurs 9. En
resultatredovisning.
Texts chosen from Skrivbanken.se
For the year 1992: 102151,102157, 102202, 112105, 112148, 102160,
115030, 115155, 150040, 150120, 162036, 186005, 302103 and 325101.
75
For the year 2003: 113309, 207111, 207115, 258315, 281121, 101213,
101214, 101309, 114116, 121115, 114224, 195325, 413202, 875115 and
881219.
76
Good Tag Hunting:
Tagability of Granska Tags
Eva Forsbom
Uppsala University
Department of Linguistics and Philology
1
Introduction
Part-of-speech (or rather morphosyntactic) tagging is an important preprocessing step in most natural language processing applications, even in applications
where full parsing is performed, such as rule-based machine translation.
For Swedish, the Stockholm-Umeå Corpus (SUC, Ejerhed et al., 2006) has
become the de facto standard for training and evaluating part-of-speech taggers
for Swedish. It is a balanced corpus, intended to be representative of general,
written, published, Swedish. Two interchangeable tagsets are used: the SUC
tagset (Ejerhed et al., 1992), and the PAROLE tagset. In this paper, only the
SUC tagset is used, but as the two tagsets are interchangeable, any findings
will apply also to the PAROLE tagset.
Although the SUC tagset covers most of the morphosyntactic features used
in Swedish, it does not cover everything. In order to approve the situation,
the SUC tagset was altered to fit the needs of the Granska grammar checker
(Carlberger and Kann, 1999). In the Granska tagset, some features were added
to the morphosyntactic features represented in the SUC tagset, and some lowfrequent features were removed. When taggers using the same learning algorithm with the SUC and the Granska tagset, respectively, were trained and evaluated on SUC, the one with the Granska tagset performed better (Carlberger
and Kann, 1999), and I have noticed the same effect in my own experiments.
However, no analysis has been done on the effect of the individual changes to
the tagset.
Based on my knowledge of Swedish, I suspected that some of changes were
more influential than others, such as the differentiation of main and auxiliary
verbs, and the conflation of some participle tags with the corresponding adjective tags. I also suspected that the removal of some features was actually
harmful, such as the abbreviation feature. Furthermore, I doubted the usefulness of the addition of two semantic features: date (e.g., januari ‘January’) and
set (e.g., meter in 10 meter), as they are not morphosyntactic in nature.
77
In this paper, I have analysed the effect of groups of related changes in the
Granska tagset, in the hope of hunting down a set of good tags that could
improve the SUC tagset.
2
Background
2.1
SUC Tagset
SUC is a balanced corpus of modern Swedish prose covering approximately 1
million word tokens, with manually validated part-of-speech annotation. The
manual validation, and the inclusion of several genres, makes it an excellent
choice for tagger training and evaluation. The texts are from the years 1990 to
1994, and the basic idea of the compilation was that it should mirror what a
Swedish person might read in the early nineties. It has been published in two
versions. The second version contains the same text samples, but has corrected
(and additional) annotations. Carlberger and Kann (1999) used version 1.0.
For this paper, version 2.0 is used.
Of the two tagsets present in SUC, only the SUC tagset is used here. It has
22 main categories, such as noun and verb, and a set of morphosyntactic features to make further distinctions within the main categories, such as gender,
number, voice, and form. A tag for a neuter, singular, indefinite, nominative,
common noun, for example, would be NN NEU SIN IND NOM (or in Granska
format nn.neu.sin.ind.nom).
All in all, the SUC tagset consists of 153 different tags1 , many of which occur only a few times (45 occur less than 100 times, and 23 less than 10 times).
With such a large tagset, some of the trigram statistics for a trigram tagger will
be unreliable (average trigram count is 16 times, and 17% of the trigrams occur only once). This data sparsity was one of the reasons for adapting the SUC
tagset.
2.2
Granska Tagset
The Granska tagset is an automatic adaption of the SUC tagset to better suit
the purposes of a grammar checker. Adaptation was done in two ways. Firstly,
some of the least occurring tags were matched with similar tags and two or
more tags were merged into one tag. In this way, the number of tags were
reduced, and the most unreliable tags, from a learning perspective, were removed. Secondly, a number of new features were introduced, where the original tagset was not detailed enough, such as adding a distinction between main
verbs, and auxiliaries, copulas and modal verbs, respectively, and a distinction
between singular and plural cardinals. All in all, 14 tags were removed and 5
new tags added (Carlberger and Kann, 1999).
1
78
140 in version 1.0, according to Carlberger and Kann (1999)
Change group
Copulas (kop)
Past participles (pc)
Auxiliaries (aux)
Modals (mod)
Dates (dat)
Singulars (sin)
Adjectives (jj)
Genitive participles (pc.gen)
Masculines (mas)
S-forms/Active forms (sfo)
Sets (set)
Abbreviations (an)
Example
vara, (för)bliva, heta, kallas
pc.prf.utr/neu.plu.ind/def.nom →
jj.pos.utr/neu.plu.ind/def.nom
ha
lära, måste, behöva, tänka, försöka, förefalla, söka, ska,
böra, töras, kunna, börja, våga, bruka, sluta, låta, få,
hinna, verka
måndag(en), tisdag(en), januari, februari
1, i
jj.pos.utr/neu.plu.ind/def.gen →
jj.gen
pc.prs.utr/neu.sin/plu.ind/def.gen →
pc.gen, pc.prf.utr/neu.sin.def.gen →
pc.gen
dt.mas.sin.def → dt.mas.sin.ind/def,
dt.mas.sin.ind → dt.mas.sin.ind/def
vb.imp.sfo → vb.imp, vb.imp.akt →
vb.imp
kilo, meter, familj, armada
nn.an → nn, ps.an →
ps.utr/neu.sin/plu.def
Table 1: Tagset groups.
No attempt was made to evaluate the effect of each individual adaptation,
although the full adaptation was evaluated, and found to give slightly better
performance results than the original tagset (2%).
The conversion of SUC tags to Granska tags was done automatically by a
lexer. I did not have access to the original version of the lexer used in Carlberger and Kann (1999), but had a newer version, and a version of SUC with
Granska tags converted with the original version. The newer lexer was ported
to Perl, and harmonised with the Granska-versioned SUC. The lexer rules were
divided into groups of similar changes, which could be turned off or on. An
overview is given in table 1.
Three groups concern differentiation between main verbs and auxiliary verbs:
copulas, (temporal) auxiliaries, and modal verbs, each with an extra feature
added (kop, aux, mod). This differentiation was actually present in an earlier version of the SUC tagset (Ejerhed et al., 1992), but is removed in the
current version. As the Granska conversion lexer assigns the additional features automatically, no distinction is made between, for example, the copula,
passive-constructing, or existential reading of vara ‘be’, or the temporal auxiliary or main verb ha ‘have’. Although most occurrences in SUC of those verbs
could be classified as auxiliaries, some could not, thus introducing some noise
in the corpus.
One group takes care of the removal of the voice feature (s-forms, sfo, and
active forms, akt) of imperatives and conjunctives. S-forms are either passive
or deponential forms of a verb, as in hoppas ‘jumping’ or hoppas ‘hoping’.
79
Two groups concern past participles. The first group conflates past participles and the corresponding adjective (positive) form to the same tag, e.g., handikappade ‘handicappeds’ with tag pc.prf.utr/neu.plu.ind/def.nom
would get the tag jj.pos.utr/neu.plu.ind/def.nom. The other group
conflates all genitive forms of participles to one single tag, so handikappades
‘handicappeds” with tag pc.prs.utr/neu.sin/plu.ind/def.gen would
get the tag pc.gen.
Another group deals with the conflation of adjective tags. Genitive forms
are merged into one tag, as with past participles. Three rules also conflates the
infrequent tags of three word forms into a more frequent tag: rätt ‘right’, flest
‘most’, and the compound part äldre- ‘elderly’.
Yet another group conflates tags for determiners with masculine forms into
a common tag. The rules concern three word forms: denne ‘this’, själve ‘himself’, and samme ‘the same’.
One group removes the abbreviation feature from tags. For example, the
tag for the abbreviated form proc ‘per cent’ would change from nn.an to nn.
There are also a couple of rules that adds features to the shortened tag to conflate it with an existent tag. The rules include the determiner d ‘the’, some
adjectives (f_d ‘former’, St ‘Saint’), two past participles (tf ‘acting’, adj ‘adjoint’), and the possessive pronoun h:s ‘her’.
The last morphosyntactic group adds the number feature value sin to singular cardinals or ordinals, i.e., 1 and i.
Finally, there are two semantic groups. The first deals with date expressions,
and adds the feature dat to words representing months and days. The second
with set expressions, and adds the feature set to words representing measurements (e.g., kilo and meter), indefinite numbers (e.g., femtiotal ‘some fifty’
and, more questionable, femtiotalet ‘the 50’s’), and group words (e.g., familj
‘family’ and armada).
3
Experiments
In order to try the goodness of each group of adaptations when it comes to
tagging performance, I used the statistical TnT tagger (Brants, 2000) to train a
number of models. The models were evaluated using 10-fold cross-validation2
on SUC, with and without the current adaptation under scrutiny. Both training
and testing was done with the tagger’s default settings3 , i.e., no parameter
optimisation.
For feature optimisation, I use a forward selection strategy. First, each
group of adaptations is tried in isolation to see whether they are significant
2
The cross-validation set is available at http://stp.lingfil.uu.se/~evafo/
software/cross_validation_sets.txt.
3
During training the -c flag, for internal case-labelling of tags, was used, as this generally
gives better performance for Swedish.
80
or not. Then, all groups showing a significant change in performance are tried
in pairs to see whether the two groups affect each other, and finally, the top-3
most promising groups are combined with groups with significant combination
power.
The performance measure is accuracy, i.e., the percentage of correctly tagged
words. It is measured with the tnt-diff tool, which gives overall statistics
as well as separate statistics for known and unknown words4 . As most of the
adaptations aim at improving the performance for unknown words, this information is interesting.
Statistical significance is tested with McNemar’s chi-squared test (R Development Core Team, 2007), but since the sample size is very large, even small
changes will be significant, however useful they are in practice. Therefore,
the effect size is also estimated with an exact binomial test (R Development
Core Team, 2007).5 The effect size is the probability of success of the tested
adaptation in cases where the two taggers differ.
3.1
Single Groups
The performance for single groups is shown in table 2. As can be seen, the copula and past participle groups contribute most to the improved result. These
groups explain most of the boost in performance for known words. Although
the size of the tagset increases for copulas, the extra tags makes it easier to
distinguish the rather stable, copula-specific, trigrams from other trigrams including other verbs.
The set and abbreviation groups slightly harm the performance, but the
change is not significant. All other groups improve the accuracy, although the
change for the voice group is not significant, and for the masculine and modal
groups is only mildly significant. The improvement is particularly visible for
unknown words.
For the modal group, the probability of success is almost fifty-fifty, which
makes it a rather unsafe (automatic) adaptation. A probable explanation is
that among the main verb–auxiliary distinction groups, this is the group which
contains most borderline cases.
3.2
Pairwise Groups
The performance for pairwise groups is shown in table 3. The copula and
past participle group pair did answer for almost all the improvement. No pairs
harmed the performance, but two groups did not improve the performance in
any pairing: masculines and genitive participles (except for pc.gen + aux),
which makes these adaptations less useful for tagging purposes.
4
5
The proportion of unknown words is 7.87±0.20 for all models.
Two-sided, at 95% confidence level, with a null hypothesis of 0.5% success.
81
Group
No change
All∗∗∗
kop∗∗∗
pc∗∗∗
aux∗∗∗
mod∗
dat∗∗∗
sin∗∗∗
adj∗∗∗
pc.gen∗∗
mas∗
sfo
set
an
Tagset
size
153
152
160
144
157
158
155
155
145
149
152
151
157
146
Overall
95.52±0.15
95.68±0.14
95.60±0.14
95.60±0.14
95.53±0.14
95.52±0.14
95.52±0.14
95.52±0.15
95.52±0.15
95.52±0.15
95.52±0.15
95.52±0.14
95.52±0.14
95.52±0.15
Accuracy (%)
Known
96.31±0.13
96.42±0.13
96.39±0.13
96.33±0.13
96.32±0.13
96.32±0.13
96.32±0.13
96.31±0.13
96.31±0.13
96.31±0.13
96.31±0.13
96.31±0.13
96.31±0.13
96.31±0.13
Unknown
82.26±0.99
87.10±0.91
86.36±0.96
87.04±0.91
86.30±0.99
86.27±0.97
86.26±0.99
86.25±0.99
86.27±1.00
86.27±0.99
86.26±1.00
86.27±0.99
86.23±0.98
86.25±1.00
Prob. of
success
61 (60-62)
63 (61-64)
65 (63-67)
57 (54-59)
52 (50-54)
66 (61-72)
64 (57-70)
64 (56-72)
66 (54-76)
67 (52-80)
61 (49-72)
50 (46-53)
49 (45-53)
Table 2: Performance per group (10-fold cross-validation), sorted in decreasing order of performance (higher precision not shown here). ∗∗∗ means significant at α = 0.001, ∗∗ at α = 0.01, ∗ at α = 0.05.
The modal group slightly improves the result in pair with the auxiliary, date,
singular, and adjective group, so it seems that in combination with those it is
less riskier, and a potentially good adaptation. However, in combination with
the copula and past participle group, it slightly harms the performance.
3.3
Top Groups
Both the single-group and pairwise-group experiments showed that the adaptations in the copula and past participle groups are highly motivated, in isolation
as well as in combination. The auxiliary group also showed high potential,
while the masculine and genitive participle groups had little effect. This leaves
four mildly potential groups: modals, singulars, dates, and adjectives, which
are added one by one, and so on, to the top-3 combination of copulas, past
participles, and auxiliaries. The results are shown in table 4.
It is clear that the singular and date groups somewhat improves the performance. The changes in the singular group has a higher probability of success
than those in the date group, but fewer instances, and therefore a lower impact on the performance. One explanation could be that there are more fixed
phrases with dates than with singulars, and that by adding the date feature, the
model could distinguish those phrases from other noun phrases more easily. If,
for some reason, a pure morphosyntactic tagset is preferred, the date feature
can be used during tagging, and then removed, as no other information is lost
in the process.
The modal group still has a negative effect on the performance, although the
change is not significant, while the adjective group has a small, non-significant,
82
kop
pc
aux
95.60
95.68 95.61
63%
95.60
65%
95.61
65%
95.53
61%
63%
57%
kop
pc
aux
mod
dat
sin
jj
pc.gen mas
95.60
95.61
95.61
95.61
95.60
95.60
95.60
95.60
95.60
95.60
95.60
95.60
95.54
95.54
95.54
95.54
95.54
95.53
95.52
95.53 95.53 95.53∗∗
52%
95.52
54%
95.53 95.53
66%
95.52
53%
63%
95.53
64%
95.52
53%
66%
65%
64%
mod
60%
60%
54%
dat
63%
65%
58%
sin
63%
65%
58%
jj
63%
65%
57%
pc.gen 63%
65%
57%
52%
66%
65%
64%
mas
65%
57%
52%
66%
65%
66%
63%
95.52∗ 95.52∗
95.52
95.52
95.52
95.52
95.52
95.52
95.52
95.52∗
66%
95.52
65%
67%
Table 3: Combinations of groups. Accuracy is reported in the upper right
triangle (σ is 0.14 or 0.15 for all combinations), while probability of success
is reported in the lower left triangle. ∗∗ means significant at α = 0.01, ∗ at
α = 0.05, the rest at α = 0.001.
positive effect. There are simply too few change instances in the adjective
group to tell if the changes are good or bad.
The best and safest combination, then, would be one with the copula, past
participle, auxiliary, date, and singular groups.
4
Conclusion
In conclusion, it seems as if my initial suspicions about the tagset changes
were partially correct. The added distinction between main and auxiliary verbs
was beneficial for copulas and temporal auxiliaries, but maybe not for modal
verbs, at least not without manual inspection. I also believe that the results
for copulas and temporal auxiliaries could be improved if the noise introduced
was removed.
The conflation of past participle tags with the corresponding tags for adjectives also proved to be a good change, for tagging purposes. If information on
past participles is needed, for example, for parsing, the information could not
trivially be retrieved in a later stage.
Other changes gave a more subtle, but significant, boost to performance,
such as adding the number feature singular to singular cardinals and ordinals,
and the semantic feature date to names of days and months.
83
Combination
kop + pc + aux
+ mod
+ sin∗∗∗
+ dat∗∗∗
+ jj
+ mod + sin
+ mod + dat
+ mod + jj
+ sin + dat∗∗∗
+ sin + jj∗∗∗
+ dat + jj∗∗∗
+ mod + sin + dat
+ mod + sin + jj
+ mod + dat + jj
+ sin + dat + jj∗∗∗
+ mod + sin + dat + jj
Accuracy
95.68±0.14
95.68±0.14
95.68±0.14
95.68±0.14
95.68±0.14
95.68±0.14
95.68±0.14
95.68±0.14
95.69±0.14
95.68±0.14
95.69±0.14
95.68±0.14
95.68±0.14
95.68±0.14
95.69±0.14
95.69±0.14
Prob. of success
64 (62-65)
49 (47-52)
64 (57-71)
61 (55-68)
58 (47-69)
51 (49-53)
51 (49-53)
50 (48-52)
62 (57-67)
65 (58-71)
63 (57-69)
51 (49-54)
51 (49-53)
51 (49-53)
62 (57-67)
52 (50-54)
Table 4: Combinations with the top-3 combination, evaluated against the top-3
combination. ∗∗∗ means significant at α = 0.001, the other changes are not
significant.
Some changes had very few actually changed instances in the corpus, so
they are still dark horses. Two such related changes are the conflation of several low-frequency genitive participle and adjective tags into two single tags
(pc.gen and jj.gen). I suspect that a conflation with a corresponding noun
tag would give more generalisation power, as the words are used as nouns.
The change, however, is not trivial, as the participles and adjectives are more
underspecified than the occurring noun tags.
Potentially harmful, although the change in performance was not significant,
were the removal of the form feature abbreviation, and the addition of the
semantic feature set to words representing groups of something.
To add up, the best and safest combination of changes to the SUC tagset,
given the results of the experiments, would be one with changes for copulas,
past participles, auxiliaries, dates, and singulars.
Acknowledgements
Thanks to Johan Hall, Jens Nilsson, Joakim Nivre (Växjö University) for the
SUC version with Granska tags, and to Jonas Sjöbergh (KTH) for the Granska
tag lexer.
84
References
Brants, T. (2000). TnT - a statistical part-of-speech tagger. In Proceedings of
the Sixth Applied Natural Language Processing Conference (ANLP-2000),
Seattle, Washington.
Carlberger, J. and V. Kann (1999). Implementing an efficient part-of-speech
tagger. Software Practice and Experience 29(9), 815–832.
Ejerhed, E., G. Källgren, and B. Brodda (2006). Stockholm-Umeå corpus
version 2.0, SUC 2.0. Stockholm University, Department of Linguistics and
Umeå University, Department of Linguistics.
Ejerhed, E., G. Källgren, O. Wennstedt, and M. Åström (1992). The linguistic
annotation system of the Stockholm–Umeå corpus project. Report DGLUUM-R-33, Department of General Linguistics, University of Umeå.
R Development Core Team (2007). R: A Language and Environment for Statistical Computing. Vienna, Austria: R Foundation for Statistical Computing.
85
How to Build an Open Source
Morphological Parser Now
Kimmo Koskenniemi
University of Helsinki
Department of General Linguistics
1
Introduction
This article compares the building of a morphological parser or analyzer some
20–25 years ago to the same task now. Much has changed but some tasks
remain quite similar even if computers have now perhaps 10,000 times larger
memories and disks than then, and their processing speed has become faster
by a comparable ratio.
The building of a morphological parser has become less laborious and faster,
but not by a similar factor. The speed and capacity of the computers is not the
key factor in this case. The bottleneck is still the manual work and linguistic
skill that is required, But, the availability of useful language resources and the
emergence and the spreading of new techniques and methods makes a great
difference when building a morphological parser.
A morphological parser is a central component in many larger applications
and systems of language technology. These often have different requirements,
and therefore the researchers need to test, modify and improve the parser in
various ways. Modification and flexible use of commercial products is not
easy, and therefore the open source aspect in producing a morphological parser
has become relevant and is also discussed.
2
How We Did It in the Past
Morphological parsers were not considered particularly interesting in the 1960s
and 1970s. We usually explain this by noting that English morphology is so
simple that the task is too trivial to deserve much attention. Other languages
were studied to a much lesser degree, and furthermore, every language appeared to have a unique solution. Among the early pioneers were Staffan Hellberg who lemmatized the Swedish frequency dictionary (1971), Anna Sågvall
who designed an inflectional analysis of Russian (1973), Jean Meunier, Jean
Boisvert and Francois Denis who did it for French (1976), and M. L. Hann for
German (1974, 1975).
86
Serious interest in the general aspects emerged soon after a wider array of
languages was treated, most notably Martin Kay’s early work (1977), and subsequent investigations of Anna Sågvall Hein on the applicability of Kay’s general parsing methods to Finnish inflection (1978, 1980). These were soon followed by experiments by Benny Brodda, Gunnel Källgren and Fred Karlsson
in the framework of BETA rewrite rule systems e.g., (Källgren, 1981), and a
TEXFIN system of linked minilexicons by Lauri Karttunen and his students
(1981).
The basic work of Ron Kaplan and Martin Kay in the 1970s and 1980s was
published quite late (Kaplan and Kay, 1994) but it affected the contemporary
work in early 1980s. Their work resulted in a framework of finite-state transducers where phonological alternations could be described in bidirectional
manner, and gave also rise to the two-level morphology (Koskenniemi, 1983)
which was easier to implement on computers of those days.
2.1
Handling the Inflection
Most of us who built morphological parsers in the early days, started with
inflectional rules by picking example words. The morphophonological alternations and the choice of allomorphs in their inflectional forms were carefully
studied. Everything had to be described in terms which were explicit enough
for the computer. Often this required some reorganization of the inflectional
classes listed in dictionaries and grammars. In essence, we had to
• establish classes for lexemes where each class was homogeneous enough
to allow similar mechanical inflection within them and
• implement an inflectional mechanism for each class, so that any new
lexemes entered to that class will be correctly inflected
Actually, most parsing methods of that time were not bidirectional enough to
let the linguist design the parser by thinking in terms of generating the word
forms and then just using the parser in the reverse direction for analyzing word
forms. The testing was, therefore, more time consuming and less reliable than
now because tools, such as the Xerox LEXC and XFST readily produce full
sets of inflectional paradigms which can be inspected for correctness and completeness (Beesley and Karttunen, 2003).
2.2
Accumulating the Lexicon
Once the example words seemed to function properly, one started to extend the
lexicon. One usually had to follow the hard way, and find the words one by
one. One had to determine the inflectional characteristics of each lexeme using
one’s linguistic intuitions. Only few builders of parsers were lucky enough to
have a computer readable dictionary at their disposal. In this way, much work
could be saved by reusing large vocabularies compiled by others.
87
Quite often, though, one could use existing frequency dictionaries or word
form frequency lists computed from the modest corpuses available in those
days. Using such word lists, one could start with the most relevant words and
reach a fair coverage for the parser.
After some initial vocabulary was included, one tested the parser against
corpus texts and incrementally added words encountered in corpuses which
failed to be recognized. In this way, the parser was enhanced and extended
while it was used. Many of the remaining bugs in the inflectional endings
and rules were detected while the lists of unrecognized word forms were studied. Overgeneration, i.e., cases where the parser would accept ungrammatical
combinations of stems and endings would not be easy to detect in this way.
3
What Is Easier Now
In addition to more powerful computers, we now have more data at our use
and we have technologies such as finite-state calculus, and machine learning
methods, not to mention handy scripting languages such as Python and Perl.
3.1
More Data Available
Nowadays, we have lots of computer readable texts available, maybe 100–
1000 times more than 25 years ago. This helps the building of morphological
analyzers, of course, because larger corpuses contain instances of a larger set
of lexemes. Larger corpuses also have occurrences of lexemes in several inflectional forms which makes it possible to guess the base form and inflectional
characteristics of such new lexemes. Evidence from several distinct inflected
forms makes hypotheses more likely, and having several occurrences of a word
form reduces the probability of it being an accidental typo. We have much
more data to be processed, but the improvement of the computers more than
compensates this.
Much textual data is available in various language banks where researchers
can use them, and in collections of international distribution agencies such
as Evaluations and Language Resources Distribution Agency (ELDA) or Linguistic Data Consortium (LDC) from where (even) commercial users can buy
copies of corpuses.
Another new source of text data is the Internet. The web contains enormous
amounts of data accessible for the interested users. One can easily test the
power of Internet as a source by using a search engine such as Google. Just
take a neologism and look for occurrences of its different inflectional forms
(assuming that Google searches for exact occurrences of forms without any
attempts to normalize the occurrences to their base form).
You can try the power of such web corpus data with some newly invented
verb such as a Finnish verb larpata ’performing live action role-playing (LARP)’.
Such a word could not be present in any older lexicon, as the concept and ac-
88
tivity is fairly recent. One can go ahead and test whether inflectional forms
of such a (hypothesized) verb occur in the Internet. There will actually be
plenty of hits for all common verbal forms such as larppasivat, larpataan,
larppaan. If you try hypothesized nominal inflections of larpata such as
larpatassa you will not get any hits (or at most sporadic misspellings).
As soon as we have a hypothesis of a lexeme and its inflection, we can thus
test the hypothesis against the corpuses or the Internet. Competing hypotheses
can be ranked and the most likely one chosen.
3.2
Finite-State Calculus
The use of finite-state machines and transducers in language processing apparently dates back to Zellig Harris and the late 1950s according to Joshi
and Hopely (1996). C. Douglas Johnson’s discovered how phonological rules
can be described with finite-state transducers (Johnson, 1972), but it was the
work of Ronald Kaplan and Martin Kay that made the finite-state calculus in
computational linguistics popular. Now this calculus forms the back bone of
Xerox language technology. The finite-state methods have in the course of
time gained wide use and are also available also as open source implementations such as OpenFST (see Allauzen et al., 2007, for details), SFST by Helmuth Schmid at the University of Stuttgart (2005) and Vaucanson by Jacques
Sakarovitch et al., (see Lombardy et al., 2004).
Finite-state methods were present in the early morphological parsers of the
two-level model, but then only in a limited extent. For example, in the original and the SIL PC-KIMMO (Antworth, 1990) implementation, the lexicon
is treated as a linked set of letter trees, even if it could as well be represented
as a theoretically more streamlined and clean transducer. The early rule transducers were constructed manually (and in the PC-KIMMO program this is still
the most common case). With up to date technology, lexicons and rules can, of
course, be compiled to transducers and then intersected and composed into one
single transducer of reasonable size. This allows for optimization and better
speed at run time.
The OpenFST, SFST and Vaucanson software packages are quite robust and
efficient basic finite-state calculi and they can be used in full scale language
technological projects. What they lack, is the kind of sophisticated user interfaces (such as XFST, LEXC, TWOLC) which Xerox has developed on top of
its finite-state library.
3.3
Automatic Discovery of Lexical Information
Machine learning could aim at different levels in retrieving lexical information
out of texts. A language independent approach such as what Krister Lindén
has followed, might concentrate in finding good guesses for single unknown
word-forms based on regularities acquired from training data presenting pairs
89
of base forms and their inflected forms (Lindén, 2008). On the basis of such
a guesser, the linguist might process unknown words from new texts more
efficiently with much less manual work than in the traditional scheme.
Another approach is to build a guesser as a variant of a finite-state morphological parser where the actual stems of words have been replaced by wild
card expressions allowing any phonologically possible stems, as proposed in
Beesley & Karttunen (2003). This type of an analyzer outputs usually several
possible base form plus morphosyntactic feature combinations. Thus, it is not
optimal as a starting point for collecting new lexical entries if used for isolated
word tokens. On the other hand, if we process a large batch of word-forms at a
time, their collective evidence helps. If there are several forms of a single lexeme in the data, each of them will lead to the correct candidate as a common
one. Each word-form will also give rise to sporadic other candidates which
will be less frequent. It can therefore be expected that the base forms which
are proposed based on many distinct forms are more likely correct than those
proposed by fewer forms. With some tuning, this method can produce large
amounts of lexical entries for the less frequent lexemes.
4
Copyrights and Licenses
The use of automatic methods depends more on the availability of data in sufficient quantities. The use of most published materials are controlled by a
commercial publisher. In order to get copies of materials or in order to use
them, one needs to sign a license or otherwise agree on some restrictions. Earlier parsers are also useful if available, but they too are often controlled by
commercial companies.
4.1
Protecting Copyrights
International agreements and European legislation protects the author’s copyright to a literary work. These general restrictions as such would not hinder
the development of morphological parsers. Problems arise because commercial interests are associated with the published texts. The publisher is usually
the party that has acquired some exclusive rights and it also possesses the electronic copy of such works.
The electronic versions of texts and other published materials are particularly valuable for the publishers and sensitive because, in electronic form,
the materials can be copied without much effort and with no loss in accuracy.
Thus, it is understandable that publishers are often reluctant in releasing their
texts at all, even if appropriate licenses and agreements would be signed. A
publisher may rightfully think that there is little to win and a lot to lose. If a
material leaks to the Internet, there is no way to undo the loss. The institute
or researcher causing the damage will most probably be unable to compensate
the damage.
90
Many publishers, however, consider language technological modules useful for their core operations. Therefore many publishers are willing to take
controlled risks by licensing their texts for research use, but then they need
partners and arrangements which they can rely on. A part of these arrangements consists of licenses which the users must sign and comply with. The
problematic point with these licenses is that they often are too strict.
It is quite typical that the publisher only allows academic use and forbids
any commercial use. Furthermore, the license often requires that the materials
must remain within the premises or computers of the institute. This used to
be quite acceptable in the era of mainframe computers, but nowadays, many
researchers would prefer to have a copy of the material on their desktop computer or accessible through the net.
4.2
Protecting Products and Markets
Commercial owners of parsers typically have an interest to prevent competition
on a market where they have a product. Thus they do not let even academic
researchers, let alone other commercial companies, to have the source code of
the programs or source files of lexicons of their products. The improvement or
adjusting parsers to specialized or more challenging needs is not possible.
Sometimes, the owner of a parser would allow the user to improve the system indirectly by sending feedback. In such cases, the commercial company
usually requires the full control over such additions. This may discourage the
academic users so that they have no motivation to produce substantial additions
or revisions to such products.
4.3
Open Source Aspects
Open source is a way of allowing and encouraging joint development of free
software. There are many open source licenses, and many more which refer to
another aspect of freeness, i.e., the fact that they do not charge for the program.
Here, we stress the freeness in a way the General Public License (GPL) interprets it, i.e., that one is free to modify and use and do almost anything except
transform the free program into a non free one.
Open source licenses like GPL do not allow restrictions for their use, e.g., a
GPL program may not forbid any type of use, not even commercial use. This
requirement contradicts with restrictions for exclusively academic use, which
is often stated for corpuses, not to mention digital lexical materials.
5
A Plan and Work in Progress
We have started a project is called “Open source Morphology for Finnish”, or
OMorFi which aims to produce a morphological parser which could be freely
91
modified and developed for research purposes, but also used as part of open
source software.
5.1
Initial Lexicon
The Research Centre for Languages in Finland (Kotus) as published a word
list under the Lesser General Public License (LGPL) which allows the use of
the word list and works derived from it in conjunction with other (even non
free programs). The list contains about 100,000 word entries with information
on their inflectional and consonant gradation characteristics. OMorFi uses this
list as a starting point and aims at producing a parser under the LGPL license.
Mr. Tommi Pirinen is completing his Master’s thesis on converting the
above word list into the formalism of SFST finite-state package (Schmid, 2005).
This thesis work makes the verb, noun and adjective entries operational, but
omits adverbs, pronouns etc. in the first stage. The word list being under
LGPL and SFST under GPL license, the resulting transducer is clearly still
under LGPL license, because a computer program does not create intellectual
works and the GPL license does not imply any additional claims on the output
of a such a free program.
5.2
Extending the Lexicon
The Language Bank of Finland includes texts totaling to some 100 million
word tokens under a license which allows their use both for research purposes
and for producing language technological modules which do not violate as
such the original copyright of the text. Using this material, one may produce
further entries using the above methods. When included in the word list, these
new ones will also fall under LGPL.
If all contributors are required to submit their additions under LGPL and
tools, such as heuristic programs to extract lexical entries, under GPL or LGPL,
then the improving result stays safely under LGPL. On the other hand, it appears to be vise to follow the practices of Mozilla.org and require that the
contributors share their copyright with the department or the university. Thus,
there is some party which can issue all of the resulting system under other licenses, if that turns out to be needed in future. This may indeed, be necessary
when combining a parser with other open source software, if the other license
is not directly compatible with GPL or LGPL.
5.3
Further Tools
The SFST is not quite as convenient as the Xerox tools for describing Finnish
morphology. The treatment of morphophonological alternations is a bit clumsy
as the full compilation of two-level rules is not supported as nicely as in the
Xerox TWOLC. The description of the rich sets of endings and their sequences
92
is also less natural in SFST than in Xerox LEXC which supports the concept
of interlinking sublexicons.
Thus, one student, Miikka Silfverberg, is in the process of implementing
a two-level compiler on top of the SFST finite-state calculus. He will use
the formulas invented by Anssi Yli-Jyrä which simplifies and generalizes the
compiling of the rules into transducers. Another student may start a project
on producing an open source lexicon compiler on a similar platform. Multiple
compatibility between some existing systems such as the SFST, PC-KIMMO,
XFST and versions of the original two-level implementation is aimed.
In addition to SFST, there are other open source implementations of the
finite-state calculus, most notably OpenFST and Vaucanson. A work is in
progress to produce an interface layer, HFST (Helsinki FST), which provides
a unified API for these three. Then, the finite-state tools would become more
independent from any particular basic finite-state software they are using. One
can then select the fastest or otherwise best package for a particular task. Such
a setting is expected to boost the tuning and development of the packages by
their original developers.
Other uses for the tools are also possible. Using the resulting transducers
would be particularly easy in web applications because the code needed for
running a transducer is very simple. Any language and several different types
of applications can be handled with the same simple code. Such web pages
could, of course, demonstrate the current capabilities of the morphological
parser and attract more contributors and users as well as implement directly
useful information retrieval or other functions.
Yet another possibility is to implement an intelligent entry generator which
would be open for the public. Many users of open source software, such as
OpenOffice, would probably be motivated to contribute to the enhancement
of the lexicon and spend some effort in order to benefit from better spelling
checking in future. They could use a service where such cooperative users can
enter missing words using a web page which dynamically assists in determining the exact inflectional properties of the words to be added.
5.4
Future
The European Union has started the preparatory phase of an infrastructure
called CLARIN, Common Language Resource and Technology Infrastructure.
Quite soon, there will bee a need for dozens of morphological parsers to support the multilingual services of CLARIN. It would be very useful for the
design and maintenance of CLARIN software, if all these language modules
would be software-wise compatible. Finite-state transducers would be almost
optimal in this sense, as the common programs only need to run different transducers. There is no need to program language specific features because a suitable transducer for each language (which are data for the programs), can han-
93
dle those idiosyncracies. Wide ranges of languages, even minority languages
can, thus, be served with the same run time program.
References
Allauzen, C., M. Riley, J. Schalkwyk, W. Skut, and M. Mohri (2007). Openfst:
A general and efficient weighted finite-state transducer library. In J. Holub
and J. Zdárek (Eds.), CIAA, Volume 4783 of Lecture Notes in Computer
Science, pp. 11–23. Springer.
Antworth, E. L. (1990). PC-KIMMO: a two-level processor for morphological
analysis. Number 16 in Occasional Publications in Academic Computing.
Summer Institute of Linguistics.
Beesley, K. R. and L. Karttunen (2003). Finite State Morphology. CSLI Publications. CSLI.
Hann, M. L. (1974). Principles of automatic lemmatization. ITL: Revue of
applied linguistics 23, 1–22.
Hann, M. L. (1975). Towards an algorithmic methodology of lemmatization.
ALLC Bulletin Summer 1975, 140–150.
Hellberg, S. (1971). En modell för upptradande af böjningsserier i ett
frekvenslexicon. Stencil, Språkdata, Göteborg.
Johnson, C. D. (1972). Formal Aspects of Phonological Description. Mouton
The Hague.
Joshi, A. K. and P. Hopely (1996). A parser from antiquity. Natural Language
Engineering 2(4), 291–294.
Kaplan, R. M. and M. Kay (1994). Regular models of phonological rule systems. Computational Linguistics 20(2).
Karttunen, L., R. Root, and H. Uszkoreit (1981). Texfin: Morphological analysis of finnish by computer. A paper read at 71st annual meeting of the
SASS, Albuquerque, New Mexico.
Kay, M. (1977). Morphological and syntactic analysis, Volume 5 of Fundamental studies in computer science, pp. 131–234. North-Holland.
Koskenniemi, K. (1983). Two-Level Morphology: A General Computational
Model for Word-Form Recognition and Produgtion. Number 11 in Publications. Department of General Linguistics University of Helsinki.
Källgren, G. (1981). FINVX — A system for the backwards application of
Finnish consonant gradation. Number 42 in Publication. Papers from the
Institute of Linguistics, University of Stockholm.
94
Lindén, K. (2008). A probabilistic model for guessing base forms of new
words by analogy. In CICling-2008, 9th International Conference on Intelligent Text Processing and Computational Linguistics, February 17 to 23,
2008, Haifa, Israel.
Lombardy, S., Y. Régis-Gianas, and J. Sakarovitch (2004). Introducing vaucanson. Theoretical Computer Science 328, 77–96.
Meunier, J., J. Boisvert, and F. Denis (1976). The lemmatization of contemporary french. In A. Jones and R. Churchhouse (Eds.), The computer in literary
and linguistic studies: Proceedings of the Third International Symposium,
pp. 208–214. The University of Wales Press.
Schmid, H. (2005). A programming language for finite state transducers. In
Proceedings of the 5th International Workshop on Finite State Methods in
Natural Language Processing (FSMNLP 2005).
Sågvall, A. L. (1973). A system for automatid inflectional analysis: Implemented for Russian. Almqvist & Wiksell.
Sågvall Hein, A. L. (1978). Finnish morphological analysis in the reversible
grammar system. In COLING-78, Information Abstracts.
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recognition. Fenno-Ugrica Suecana 3, 7–26.
95
Supporting Research Environment
for Less Explored Languages:
A Case Study of Swedish and Turkish
Beáta Megyesi
Bengt Dahlqvist
Eva Pettersson
Sofia Gustafson-Capková
Joakim Nivre
Uppsala University
Department of Linguistics and Philology
1
Introduction
Language resources such as corpora consisting of annotated texts and
utterances have been shown to be a central component in language studies
and natural language processing as they, when carefully collected and
compiled, contain authentic language material capturing information about
the language. Corpora are shown to be useful in language research allowing
empirical studies, as well as for various applications in natural language
processing. During the last decade, researchers’ attention have been directed
to building parallel corpora including texts and their translations as they
contain highly valuable linguistic data across languages. Methods have been
developed to build parallel corpora by automatic means, and to reuse
translational data from such corpora for several applications, such as
machine translation, multi-lingual lexicography and cross-lingual domainspecific terminology. Parallel corpora exist for many language pairs, mainly
European languages with special focus on Western-Europe.
In the past few years, efforts have been made to annotate parallel texts on
different linguistic levels up to syntactic structure to build parallel treebanks.
A treebank is a syntactically annotated text collection, where the annotation
often follows a syntactic theory, mainly based on constituent and/or
dependency structure (Abeillé, 2003). A parallel treebank is a parallel corpus
where the sentences in each language are syntactically analyzed, and the
sentences and words are aligned.
The primary goal of our work is to build a linguistically analyzed,
representative language resource for less studied language pairs dissimilar in
language structure to be able to study the relations between these languages.
The aim is to build a parallel treebank containing various annotation layers
from part of speech tags and morphological features to dependency
annotation where each layer is automatically annotated, the sentences and
words are aligned, and partly manually corrected. The work described here
96
is part of the project Supporting research environment for minor languages
initiated by professor Anna Sågvall Hein at Uppsala University. The project
aims at building various types of language resources for Turkish and Hindi.
We choose Swedish and Turkish, a less studied and typologically dissimilar
language pair, to serve as a pilot study for building parallel treebanks for
other language pairs. Therefore, efforts are put on developing a general
method and using tools that can be applied to other language pairs easily.
The components of the language resource are texts that are in translational
relation to each other and syntactically analyzed, and tools for the automatic
analysis and alignment of these languages. To build a parallel corpus, we
reuse existing resources and create necessary tools for the automatic
processing and alignment of the parallel texts in these languages. The
purpose is to build the corpus automatically by using a basic language
resource kit (BLARK) for the particular languages and appropriate tools for
the automatic alignment and correction of data. We use tools that are userfriendly, understandable and easy to learn by people with less computer
skills, thereby allowing researchers and students to align and correct the
corpus data by themselves. The parallel treebank is intended to be used in
linguistic research, teaching and applications such as machine translation.
The paper is organized as follows: section 2 gives an overview of parallel
corpora in general and parallel treebanks in particular; section 3 describes
the parallel treebank, the methods used for building the treebank and the
tools used for visualization, correction and investigation of the treebank. In
section 4, we suggest some further improvements and lastly, in section 5, we
conclude the paper.
2
Parallel Corpora and Parallel Treebanks
A parallel corpus is usually defined as a collection of original texts translated
to another language where the texts, paragraphs, sentences, and words are
typically linked to each other. One of the most well-known and frequently
used parallel corpora is Europarl (Koehn, 2002) which is a collection of
material including 11 European languages taken from the proceedings of the
European Parliament. Another parallel corpus is the JRC-Acquis
Multilingual Parallel Corpus (Steinberger et al., 2006). It is the largest
existing parallel corpus of today concerning both its size and the number of
languages covered. The corpus consists of documents of legislative text,
covering a variety of domains for above 20 languages. Another often used
resource is the Bible translated to a large number of languages and collected
and annotated by Resnik et al. (1999). The OPUS corpus (Tiedemann and
Nygaard, 2004) is another example of a freely available parallel language
resource.
There are, of course, many other parallel corpus resources that contain
sentences and words aligned in two languages only. Such corpora often exist
for languages in Europe, for example the English-Norwegian Parallel Corpus
(Oksefjell, 1999) and the ISJ-ELAN Slovene-English Parallel Corpus
97
(Erjavec, 2002). It is especially common to include English as one of the two
languages in the pair. Parallel corpora that do not include English or another
European language are rare.
Parallel treebanks belong to a fairly new type of language resource,
consequently we find a smaller amount of resources of this type available.
The Prague Czech-English Dependency Treebank (Hajic et al., 2001) is one
of the earliest parallel treebanks, containing dependency annotation. The
English-German parallel treebank (Cyrus et al., 2003) is another resource
with multi-layer linguistic annotation including part of speech, constituent
structures, functional relations, and predicate-argument structures. There are
also small parallel treebanks including Swedish as one of the languages
under development. The Linköping English-Swedish Parallel Treebank, also
called LinES (Ahrenberg, 2007) contains approximately 1200 sentence pairs,
annotated with PoS and dependency structures, and the Swedish-EnglishGerman treebank, SMULTRON (Gustafson-Capková et al., 2007), annotated
with PoS and constituent structures.
In most parallel corpora including parallel treebanks, we find English and
other structurally similar languages. However, there is a need to develop
language resources in general, and parallel corpora and treebanks in
particular, for other language pairs. Next, we describe the development of
our Swedish-Turkish parallel treebank.
3
The Swedish-Turkish Parallel Treebank
First, we present the content and the annotation procedure of the treebank,
then we give an overview of the tools that we use for the visualization and
correction of the corpus annotation.
3.1 Corpus Content
The corpus, which has been previously described (Megyesi et al., 2006;
Megyesi & Dahlqvist, 2007; and Megyesi et al., 2008) consists of original
texts – both fiction and technical documents – and their translations from
Turkish to Swedish and from Swedish to Turkish with the exception of one
text which is a translation from Norwegian to both languages. In table 1, the
corpus material is summarized.
The corpus consists of approximately 165,000 tokens in Swedish and
140,000 tokens in Turkish. Divided into text types, the fiction part of the
corpus includes 76,877 tokens in Swedish, and 55,378 tokens in Turkish.
The technical documents are larger and contain 90,901 tokens in Swedish,
and 85,171 tokens in Turkish. The current material presented here serves as
pilot linguistic data for the Swedish-Turkish parallel corpus. We intend to
extend the material to other texts, both technical and fiction, in the future.
98
Document: Fiction
# Tokens
# Types
The White Castle – Swedish
53232
7748
The White Castle – Turkish
36684
12472
Sofie’s world – Swedish
6488
1466
Sofie’s world – Turkish
4800
2215
The Royal Physician’s Visit – Swedish
17157
3932
The Royal Physician’s Visit – Turkish
13894
5456
Islam and Europe – Swedish
55945
10977
Islam and Europe – Turkish
48893
14128
Info about Sweden – Swedish
24107
4576
Info about Sweden – Turkish
23660
7119
Retirement – Swedish
3417
818
Retirement – Turkish
3664
1188
Dublin – Swedish
392
169
Dublin – Turkish
394
230
Pregnancy – Swedish
949
409
Pregnancy – Turkish
1042
567
Psychology – Swedish
347
193
Psychology – Turkish
281
220
Movement – Swedish
543
300
Movement – Turkish
568
369
Social security – Swedish
5201
846
Social security – Turkish
6669
2025
Document: Non-fiction
Table 1: The corpus data divided into text categories with number of tokens
and types.
3.2 Corpus Annotation
The corpus material is processed automatically by using various tools
making the annotation, alignment and manual correction easy and
straightforward for users with less computer skills. This is necessary, as our
ambition is to allow researchers and students of particular languages to
enlarge the corpus by automatically processing and correcting the new data
by themselves.
First, the original materials, i.e., the source and target texts received from
the publishers in various formats are cleaned up. For example, rtf, doc, and
99
pdf documents are converted to plain text files. In the case of the original
pdf-file, we scan and proof-read the material and, where necessary, correct it
to ensure that the plain text file is complete and correct. After cleaning up
the original data, the texts are processed automatically by using tools for
formatting, linguistic annotation and sentence and word alignment. Figure 1
gives an overview of the main modules in the corpus annotation procedure.
Figure 1: The modules of corpus annotation.
During formatting, the texts are encoded using UTF-8 (Unicode) and marked
up structurally using XML Corpus Encoding Standard (XCES) for the
annotation format. The plain text files are then processed by various tools in
the BLARKs developed for each language separately when necessary. A
sentence splitter is used to break the texts into sentences, and a tokenizer is
used to separate words from punctuation marks.
Once the sentences and tokens are identified, the data is linguistically
analyzed. For the linguistic annotation, external morphological analyzers,
part of speech taggers and syntactic dependency parsers are used for the
specific languages. We use several annotation layers for the linguistic
analysis, first on a morphological level, then on a syntactic level.
The Swedish texts are morphologically annotated with the Trigrams ’n’
Tags part of speech tagger (Brants, 2000), trained on Swedish (Megyesi,
2002) using the Stockholm-Umeå Corpus (SUC, 1997). The tokens are
annotated with parts of speech and morphological features and are
disambiguated according to the syntactic context. The results for the
morphological annotation of Swedish show an accuracy of 96.6%. The most
erroneous tags in the materials are: i) proper nouns which should be tagged
as common nouns, ii) particles which should be tagged as adverbs, iii)
prepositions which should be annotated as particles or adverbs, iv) nouns
100
with wrong morphological analysis and finally v) participles which should
be tagged as verbs. These errors constitute 46% of all errors.
The Turkish material is analyzed morphologically by using an automatic
morphological analyzer developed for Turkish (Oflazer, 1994). Each token
in the text is segmented and annotated with morphological features including
part of speech. The Turkish material is morphologically analyzed and
disambiguated using a Turkish analyzer (Oflazer, 1994) and a disambiguator
(Yuret and Türe, 2006). Evaluation of the Turkish tagging and
disambiguation shows an average accuracy of 78.6%. Problematic
confusions in the Turkish tagging seems to be between i) determiners and
numerals, ii) postpositions in nominative and postpositions in genitive, and
iii) determiners and pronouns. These errors account for 24.9% of all errors.
<s id="s11.4">
<w pos="DT_UTR_SIN_IND" head="3" deprel="DET" id="w11.4.1">Någon</w>
<w pos="JJ_POS_UTR_SIN_IND_NOM" head="3" deprel="DET" id="w11.4.2">annan</w>
<w pos="NN_UTR_SIN_IND_NOM" head="4" deprel="SUB" id="w11.4.3">titel</w>
<w pos="VB_PRT_SFO" head="0" deprel="ROOT" id="w11.4.4">fanns</w>
<w pos="AB" head="4" deprel="ADV" id="w11.4.5">inte</w>
<w pos="MAD" head="4" deprel="IP" id="w11.4.6">.</w>
</s>
<s id="s10.5">
<w pos="+Adj" head="3" deprel="MODIFIER" id="w10.5.1">Baka</w>
<w pos="+Num+Card^DB+Noun+Zero+A3sg+Pnon+Nom" head="6" deprel="SUBJECT"
id="w10.5.2">bir</w>
<w pos="+Noun+A3sg+Pnon+Nom" head="6" deprel="OBJECT" id="w10.5.3">balık</w>
<w pos="+Adj^DB+Verb+Zero+Past+A3sg" head="0" deprel="ROOT" id="w10.5.4">yoktu</w>
<w pos="+Punc" head="6" deprel="PUNC" id="w10.5.5">.</w>
</s>
Figure 2: An example of morphological and syntactic annotation in XCES
format.
The other linguistic layer contains information about the syntactic analysis.
For the grammatical description, we choose dependency rather than
constituent structures, as the former has been shown to be well suited for
both morphologically rich and free word order languages such as Turkish,
and for morphologically simpler languages, like Swedish. Both the Swedish
and the Turkish data are annotated syntactically using MaltParser (Nivre et
al., 2006a), trained on the Swedish treebank Talbanken05 (Nivre et al.,
2006b) and on the Metu-Sabancı Turkish Treebank (Oflazer et al., 2003),
respectively. MaltParser was the best performing parser for both Swedish
and Turkish in the CoNLL-X shared task on multilingual dependency
parsing (Buchholz and Marsi, 2006), with a labeled dependency accuracy of
84.6% for Swedish and 65.7% for Turkish. Currently, we manually correct
the syntactic annotation in each language. Figure 2 illustrates an example
taken from Orhan Pamuk’s book The White Castle, showing the
morphological and syntactic annotation from the formatter and analyzers for
101
the sentence “Some other title did not exist.” in Swedish and Turkish in
XCES format.
After the linguistic analysis, the sentences are aligned automatically, and
the words are linked to each other in the two languages. We use standard
techniques for the establishment of links between source and target language
segments. Paragraphs and sentences are aligned by using the length-based
approach developed by Gale and Church (1993).
Once the sentences are aligned in the source and target language, we send
it for manual correction to a student who speaks both languages. We
automatically compare the links before and after the manual correction and
the user gets statistics about the differences. The results show that between
67% and 94% of the sentences were correctly aligned by the automatic
sentence aligner depending on the text type.
Lastly, phrases and words are aligned using the clue alignment approach
(Tiedemann, 2003), and the toolbox for statistical machine translation
GIZA++ (Och and Ney, 2003). Results show that the word aligner aligned
approximately 69% of the words correctly.
In addition to the automatic morpho-syntactic annotation and alignment,
we correct the linguistic analysis and links manually, and visualize the
corpus in different ways without showing the structural markup when used,
for example, in teaching. These tools will be described next.
3.3 Tools for Visualization and Correction
In the project, our goal is to reuse and further develop freely available,
system independent, user-friendly tools for the annotation, visualization,
correction and search in our corpus, both considering the mono-lingual and
the parallel treebanks.
As basis for the annotation, we use the Uplug toolkit which is a collection
of tools for processing corpus data, created by Jörg Tiedemann (2003).
Uplug is used for sentence splitting, tokenization, tagging by using external
taggers, and paragraph, sentence and word alignment. All the essential
processing tools are implemented in a graphical interface, UplugConnector
(Megyesi and Dahqvist, 2007) which accesses both the modules in the Uplug
toolkit (Tiedemann, 2003), and other programs for linguistic annotation.
The Uplug package consists of a number of perl scripts accessible by line
commands with a large number of options and sometimes utilizing piping
between commands. To facilitate easier access and usage of these scripts, a
graphical user interface, UplugConnector, was developed in Java for the
project. Here, the user can in a simple fashion choose a specific task to be
performed and let the graphical user interface (GUI) set up the proper
sequence of calls to Uplug and subsequently execute them. Figure 3 below
illustrates the Uplug Connector interface.
The user can optionally give the location of the source and target files,
decide where the output should be saved, and specify the encoding for the
input and output files. For the markup, basic structural markup, sentence
102
segmentation, and tokenization are available. Further, the Uplug Connector
GUI has been constructed to give the possibility to include calls to new
scripts outside Uplug for complementary analysis, when such needs arise.
The user can easily access another resource if the available ones do not fit
his/her needs, for example an external tokenizer, sentence splitter, tagger or
parser. In the toolkit, the user can also call for the sentence and word
aligners and their visualization tools.
Figure 3: The Uplug Connector.
As the XML representation of the result is not user friendly even for people
used to this kind of annotation, we use various interfaces for the
visualization of the linguistic annotation and alignment results. In addition,
since the automatic alignment generates some errors, we also use tools for
the manual correction of these.
As a tool for the correction of the sentence alignment, we choose the
system ISA (Interactive Sentence Alignment) developed by Tiedemann
(2006). ISA is a graphical interface for automatic and manual sentence
alignment which uses the alignment tools implemented in Uplug. It handles
the manual correction of the sentence alignment in a user-friendly,
interactive fashion. Figure 4 shows ISA with the aligned sentences taken
from Orhan Pamuk’s book The White Castle.
103
Figure 4: ISA showing the aligned sentences from The White Castle.
For displaying the corrected sentence output from ISA after manual
correction of the alignment together with the linguistic analysis, a script
utilizing the structural XML-parser Hpricot (2006) was developed. It takes
as input the tagged XML-files for the language pair together with the XML
file containing the sentence alignment results produced by ISA and generates
an HTML-file which displays the sentences aligned together with the
morphological information for each word shown in pop-up windows as
shown in figure 5. The visualization tool makes it easier for students and
researchers to study the part of speech and inflectional features of the words
and chosen structures for translation than the structurally marked up version
of the corpus.
Figure 5: Visualization of aligned sentence pairs with linguistic annotation shown in
the pop-up window.
104
To visualize the word alignment result in a simple way, a new script for
HTML-visualization of the word alignment result was included in the
UplugConnector. This takes as input the text file with word link information
produced by Uplug, see figure 6, and shows the word-pair frequencies. This
visualization actually presents a bilingual lexicon created from the source
and target language data.
Figure 6: HTML-visualization of word alignment.
For the visualization and correction of the parallel syntactic trees, we
choose Stockholm Tree Aligner (Lundborg, et al., 2007).1 The tool allows
the user to create links between corresponding nodes in two treebanks, hence
allowing word and phrase alignment correction between our languages. The
tool also contains a search function that implements the TigerSearch Query
Language with additions for searching alignments. The visualization with
Stockholm Tree Aligner for the sentence “Some other title did not exist.” is
visualized as syntactic trees for Turkish and Swedish showing the
dependency relations between the elements in each sentence in figure 7.
4
Further Developments
In the near future, we are going to apply the automatic annotation procedure
on other languages of different types, such as Hindi and Persian and study
the differences between the language pairs and the effects on the
construction of parallel treebanks.
1See http://www.ling.su.se/dali/downloads/treealigner/index.htm.
105
Figure 7: Dependency relations in Turkish and Swedish for the same
sentence.
5
Conclusion
We have presented a Swedish-Turkish parallel treebank a less processed
language pair containing approximately 165,000 tokens in Swedish, and
140,000 tokens in Turkish. The treebank is automatically created by re-using
and adjusting existing tools for the automatic alignment and its visualization,
and basic language resource kits for the automatic linguistic annotation of
the involved languages. The automatic annotation and alignment is also
partly manually corrected. The treebank is already in use in language
teaching, primarily in Turkish.
Acknowledgments
We are grateful to Jörg Tiedemann for his kind support with Uplug, and
Kemal Oflazer and Gülen Eryiit for the morphological annotation of
Turkish. We would like to thank the publishers for allowing us to use the
texts in the corpus. The project is financed by the Swedish Research Council
and the Faculty of Languages at Uppsala University.
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110
Cultivating a Swedish Treebank
Joakim Nivre
Beáta Megyesi
Sofia Gustafson-Čapková
Filip Salomonsson
Bengt Dahlqvist
Uppsala University
Department of Linguistics and Philology
1
Introduction
Treebanks, or syntactically annotated corpora, are an invaluable resource for
the development and evaluation of syntactic parsers, as well as for empirical
research on natural language syntax. Treebanks for Swedish have a long and
venerable history, represented by the pioneering work on Talbanken (Einarsson, 1976a,b) and SynTag (Järborg, 1986). In recent years, however, treebank
development for Swedish has mostly been limited to smaller projects, such as
the reconstruction of Talbanken into Talbanken05 (Nivre et al., 2006), efforts
to create a Swedish treebank with texts from the medical domain (Kokkinakis,
2006), and development of small parallel treebanks for Swedish-English-German
(Gustafson-Čapková et al., 2007), and Swedish-English (Ahrenberg, 2007).
As a consequence, there is still no Swedish treebank of the same scale as the
largest available treebanks, such as the Penn Treebank for English (Marcus
et al., 1993) or the Prague Dependency Treebank for Czech (Hajič et al., 2001).
Given the high cost of manual annotation and post-editing in treebank development, the possibility to reuse existing annotated resources is potentially
of great importance. Often the efficient reuse of such resources is hampered
by the fact that different resources, even for the same language, have been developed with different annotation guidelines or encoding standards. In many
cases, however, it is possible to overcome these obstacles through a process of
cross-corpus harmonization and annotation projection.
In this paper, we describe an ongoing project with the aim of bootstrapping a large Swedish treebank, ultimately with a size of about 1.5 million tokens, by reusing two existing annotated corpora: the previously mentioned
treebank Talbanken, consisting of about 350,000 tokens, and the more recent Stockholm-Umeå Corpus (Ejerhed and Källgren, 1997), a part-of-speechtagged corpus of about 1.2 million words. This treebanking effort is part of the
111
project Methods and Tools for Automatic Grammar Extraction, supported by
the Swedish Research Council and initiated by Anna Sågvall Hein at Uppsala
University. Besides treebank development, this project involves research on
grammar induction with evaluation in the context of machine translation.
The paper is structured as follows. We first give an overview of the project
and the different steps needed to develop a new treebank from existing resources and then focus on the two most interesting steps: the harmonization
of tokenization and sentence segmentation, and the projection of annotation
from one corpus to the other using data-driven taggers and parsers. The latter step also involves annotation refinement, where the syntactic annotation in
Talbanken is extended and modified to better suit present-day requirements Finally, we briefly discuss how much is gained by reusing existing corpora and
annotation, as opposed to creating a new treebank from scratch.
2
Bootstrapping a Large Swedish Treebank
Our ultimate goal is to produce a Swedish treebank containing 1.5 million tokens by reusing two existing annotated corpora. In section 2.1, we describe
important properties of the two corpora; in section 2.2 we describe the major steps that need to be taken to reuse them as part of a single, consistently
annotated treebank.
P10835069001
P10835069002
P10835069003
P1083506900410002
P1083506900510002
P1083506900610002
P1083506900710002
P1083506900811003
P1083506900911003
P1083506901011003
P1083506901111003
P1083506901210002
P1083506901310002
P1083506901410002
P10835069015
P10835069016
P10835069017
P10835069018
0000
*DEN
1000
SOM
VÄNTAR
MED
1100
ATT
TA
UT
ÅLDERSPENSIONEN
TILL
EFTER
67-ÅRSMÅNADEN
FÅR
HÖGRE
PENSION
.
«
PODPHH
RC
PORPHH
VVPS
PR
IF
IM
VVIV
ABZA
NNDDSS
PR
PR
NNDDSS
FVPS
AJKP
NN
IP
GM
SS
SSET
SS
FV
OAPR
OA
IM
IV
PL
OO
TAPR
TATAPR
TATA
FV
OOAT
OO
IP
074
074
074
074
074
074
074
074
074
074
074
074
074
074
074
074
074
074
Figure 1: Annotated sentence from Talbanken: Den som väntar med att ta ut
ålderspensionen till efter 67-årsmånaden får högre pension (Those who do not
claim their old age pension until after the 67-year month get a higher pension).
112
2.1
Component Corpora
Talbanken (Einarsson, 1976a,b) is a syntactically annotated corpus, containing
both written and spoken Swedish, produced in the 1970s at the Department of
Scandinavian Languages, Lund University, by a group led by Ulf Teleman. In
total, the corpus contains about 350,000 tokens, divided into 200,000 tokens
of written text (professional prose and high school essays) and 150,000 tokens
of spoken language (interviews, debates, and informal conversations). The annotation consists of two layers: a lexical layer, with parts of speech and morphosyntactic features, and a syntactic layer, with a relatively flat phrase structure and grammatical functions (or dependencies). The annotation scheme,
known as MAMBA, is described in Teleman (1974) and illustrated in figure 1,
which shows a small extract from Talbanken.
The main asset of Talbanken, from our point of view, resides in the syntactic annotation, which contains enough information to support the extraction of
both phrase structure and dependency structure representations, as shown in
Nilsson et al. (2005) and Nivre et al. (2006), and therefore provides a good
base representation for a treebank. Moreover, since Talbanken is by far the
largest available corpus of Swedish with manually validated syntactic annotation, including it in the new treebank not only lets us reuse a manually validated syntactic annotation of 350,000 tokens, but also gives us a good basis for
training parsers that can be used in the annotation of additional data.
The Stockholm-Umeå Corpus (SUC) (Ejerhed and Källgren, 1997) is a balanced corpus of written Swedish, modeled after the Brown Corpus and similar
corpora for English, developed at Stockholm University and at Umeå University in a project led by Gunnel Källgren and Eva Ejerhed. The corpus consists
of 1.2 million tokens of text from a variety of different genres, the corpus encoding follows the guidelines of the Text Encoding Initiative (TEI), and the
annotation includes lemmatization, parts of speech, morphosyntactic features,
and named entities. Since SUC was first released in the 1990s, its annotation
scheme has become a de facto standard for Swedish, especially in research
on part-of-speech tagging, where SUC data is standardly used for training and
evaluation (see, e.g., Carlberger and Kann, 1999; Nivre, 2000; Megyesi, 2002).
The annotation scheme is illustrated in figure 2, which shows a small extract
from the corpus.
Given that SUC is a larger and more recently developed corpus, which has
been extensively used to train taggers and other tools for Swedish, it makes
sense to use SUC as a model for the new treebank wherever possible, thus
minimizing the need for (new) manual validation and maximizing the conformance with current practice in Swedish language technology. This means,
among other things, that principles of tokenization and sentence segmentation
should be kept intact in SUC but modified for Talbanken in cases of conflict.
We will refer to this as the harmonization of tokenization and sentence segmentation. The same holds for the annotation of parts of speech and mor-
113
<s id=fh06-089>
<w n=1487>Senare<ana><ps>AB<m>KOM<b>sen</w>
<w n=1488>på<ana><ps>PP<b>på</w>
<w n=1489>1940-talet<ana><ps>NN<m>NEU SIN DEF NOM<b>1940-tal</w>
<w n=1490>byggde<ana><ps>VB<m>PRT AKT<b>bygga</w>
<NAME TYPE=PERSON>
<w n=1491>John<ana><ps>PM<m>NOM<b>John</w>
<w n=1492>von<ana><ps>PM<m>NOM<b>von</w>
<w n=1493>Neumann<ana><ps>PM<m>NOM<b>Neumann</w>
</NAME>
<w n=1494>i<ana><ps>PP<b>i</w>
<NAME TYPE=PLACE>
<w n=1495>Princeton<ana><ps>PM<m>NOM<b>Princeton</w>
</NAME>
<w n=1496>i<ana><ps>PP<b>i</w>
<NAME TYPE=PLACE>
<ABBR>
<w n=1497>USA<ana><ps>PM<m>NOM<b>USA</w>
</ABBR>
</NAME>
<w n=1498>sina<ana><ps>PS<m>UTR/NEU PLU DEF<b>sin</w>
<num>
<w n=1499>första<ana><ps>RO<m>NOM<b>första</w>
</num>
<w n=1500>datamaskiner<ana><ps>NN<m>UTR PLU IND NOM<b>datamaskin</w>
<d n=1501>.<ana><ps>MAD<b>.</d>
</s>
Figure 2: Annotated sentence from the Stockholm-Umeå Corpus: Senare på
1940-talet byggde John von Neumann i Princeton i USA sina första datamaskiner (Later in the 1940s John von Neumann at Princeton in the USA built his
first computers).
phosyntactic features, where the kind of annotation used in SUC has to be
projected to Talbanken, which unfortunately uses a different scheme.1 Since
no simple mapping exists from the Talbanken scheme to the SUC scheme (nor
in the other direction), this projection will have to be induced by training a
tagger on the SUC corpus, using it to reannotate Talbanken, and finally correcting the errors performed by the tagger in a manual post-editing phase. In
the following, we will use the term morphological annotation (in contrast to
syntactic annotation) to include both basic parts of speech and morphosyntactic features.
1
Other kinds of annotation found in SUC, such as lemmatization and named entities, are
outside the scope of the current project but should in principle be projected in the same way
from SUC to Talbanken.
114
2.2
Treebank Development
Given the considerations so far, we propose the following overall plan for the
production of a new treebank based on Talbanken and SUC:
1. Convert both corpora with their existing annotation into a common standard for corpus encoding (XCES with standoff annotation).
2. Harmonize tokenization and sentence segmentation in Talbanken, applying as far as possible the principles adopted in SUC.
3. Project morphological annotation from SUC to Talbanken, using a datadriven tagger trained on SUC with manual post-editing.
4. Refine the syntactic annotation in Talbanken by automatic inference.
5. Project syntactic annotation from Talbanken to SUC, using a data-driven
parser trained on Talbanken with manual post-editing.
In the following two sections, we describe the problems involved in harmonization, annotation refinement and annotation projection in a little more detail.
3
Harmonization
To harmonize the two corpora, we convert the tokenization and sentence segmentation of Talbanken according to the principles of SUC.
3.1
Tokenization
In the tokenization of SUC, abbreviations are always represented as single tokens. This means that when abbreviations in the original text contain spaces,
the different elements are concatenated into one token where spaces in the
original text are represented by underscores. Moreover, different variants of
the same abbreviations are normalized to one form. Thus, the following variants of the abbreviation of till exempel (for example):
t. ex.
t ex
are all tokenized as one token:
t_ex
In Talbanken, on the other hand, abbreviations consisting of several elements
are annotated as multi-word expressions. Each element of abbreviation is
treated as a separate token, but only the first token is assigned proper lexical
and syntactic annotation, while the subsequent token are assigned the dummy
115
tag ID (in both the lexical and the syntactic annotation). To find the abbreviations in Talbanken, we automatically extract tokens annotated with ID tags
together with the preceding token, and convert these into a single token with
the form prescribed by SUC’s tokenization standards.
Certain numerical expressions, such as 3–5, are also tokenized differently
in the two corpora, such that SUC often has a single token where Talbanken
splits the expression into several tokens (which may or may not be annotated
as a multi-word expression). For certain types of numerical expressions, it is
again possible to perform the harmonization automatically, but most cases here
need to be checked manually.
3.2
Sentence Segmentation
The sentence segmentation also differs in the two corpora. Above all, lists
have a different structural annotation. In SUC, items in lists are handled as
different sentence units, while in Talbanken the entire list consisting of several
items is treated as one sentence if there are clear syntactic relations between the
items. This could lead to errors when we use a data-driven parser to project the
syntactic annotation from Talbanken to SUC, since the sentences in Talbanken
that would serve as training data would have a different structure compared to
the sentences in SUC that need to be parsed. Therefore, we treat each list item
in Talbanken as a separate sentence unit as far as possible.
4
4.1
Annotation Projection and Refinement
Morphological Annotation
In order to harmonize the morphological annotation of the two corpora, we
project the part-of-speech tags and morphological features from SUC to Talbanken. We do this by training the data-driven TnT tagger (Brants, 2000) on
SUC, bootstrapping the tagger by training it on a considerably larger automatically tagged corpus (Forsbom, 2005), and then applying the trained model to
Talbanken. Finally, we correct the automatic annotation manually following
SUC’s annotation principles. The result is a merged corpus with consistent
morphological annotation.
At the time of writing, all closed class words in Talbanken have been checked
and we predict that the work on morphological annotation will be completed
during the spring of 2008. One of the advantages of reusing a previously annotated corpus, even if the annotation is inconsistent, is that checking can be
speeded up by pattern matching on the combined old and new annotation. This
is convenient especially for closed word classes, where the lack of morphological features often makes the two annotation systems equivalent so that some
words need to be checked only if the new and the old annotations are inconsistent.
116
Figure 3: Refined syntactic annotation for the sentence Valfrihetens symbol
måste göras till tecken för kvinnans frigörelse (The symbol of free choice must
be turned into a sign of women’s liberation).
4.2
Syntactic Annotation
For the syntactic annotation, we have to project the syntactic analysis of Talbanken to SUC, since SUC lacks syntactic annotation. This is achieved in the
first place by training the data-driven MaltParser (Nivre et al., 2006) on Talbanken and using the trained model to parse SUC. At a later stage, we may
complement this annotation with the output of different parsers, which will
enable us to use an ensemble of classifiers to facilitate the manual correction
of the syntactic annotation.
However, before we can train parsers on Talbanken, the syntactic annotation
needs to be refined to meet the requirements of present-day language technology. The original annotation has very flat structures and lacks phrase categories
such as NP, VP, PP, etc. In order to obtain a hierarchical analysis involving
both phrase structure and dependency structure (grammatical functions), we
therefore need to do two things:
• Infer phrase categories using information about grammatical functions
(both internal and external to a given phrase) and about the parts of
speech of constituent words.
• Infer additional structure, such as NPs within PPs, VPs within VPs,
based on information about grammatical functions, parts of speech, and
inferred phrase categories.
117
The methodology for automatic annotation refinement is described in Nilsson
et al. (2005). Figure 3 shows an example of the current version of the refined
syntactic annotation. Our goal is to complete this work during the spring of
2008, which means that a first version of the entire treebank, with purely automatic syntactic annotation in the SUC part, could be released in the fall of
2008. A version where all the annotation has been checked manually remains
as a long-term goal for our efforts.
5
How Much Is Gained?
A reasonable question to ask is how much is actually gained by reusing existing
corpora, as opposed to building a new treebank from scratch, given the considerable amount of work involved in the harmonization and projection processes.
Let us therefore make an attempt at quantifying the gains and balancing them
against the disadvantages.
By reusing all the annotation in SUC and the syntactic annotation in Talbanken, we save all the work needed to manually correct tokenization, sentence segmentation, and morphological annotation of 1.2 million tokens, and
syntactic annotation of 350,000 tokens. In addition, we save the work needed
to check tokenization and sentence segmentation for 350,000 tokens in Talbanken, minus a few person weeks spent on harmonization. Finally, although
the morphological annotation of 350,000 tokens in Talbanken still has to be
checked manually, both the efficiency and the accuracy of this process can be
improved by making use of the old morphological annotation for consistency
checking.
To give just one illustrative example, the string men in Swedish can be either a coordinating conjunction (but) or a noun (injury). After projecting the
new morphological annotation from SUC to Talbanken, it was found that one
occurrence of men was tagged as a noun in the old annotation and as a conjunction in the new annotation, whereas the remaining 364 occurrences were
tagged as conjunctions in both cases. Unsurprisingly, the single occurrence
with inconsistent annotation turned out to be a tagging error, which in this way
could be detected and corrected. With very high probability, the remaining 364
occurrences are correctly tagged as conjunctions (since the old annotation has
been checked manually) and therefore do not need to be checked.2
To sum up, we see that cross-corpus harmonization and annotation projection can lead to substantial gains in the manual work needed to validate segmentation and annotation. This of course has to be weighed against a number
of other factors, in particular that the new treebank has to be based on old
data (in the case of Talbanken, texts from the 1970s) and that the annotation
2
Other examples are man, which is ambiguous between a pronoun (one) with 699 occurrences and a noun (man) with 67 occurrences, and Vi, which has a single occurrence as the
name of a magazine and 328 occurrences as a capitalized pronoun (we).
118
schemes have to be inherited from at least one of the old corpora. Still, in situations where manual effort has to be minimized, the approach taken appears
to be a viable methodology for producing a large-scale treebank from existing
resources.
6
Conclusion
In this paper, we have presented ongoing work to produce a large treebank of
Swedish by reusing two existing annotated corpora, Talbanken and SUC. A
key component in the bootstrapping methodology is the use of cross-corpus
harmonization and annotation projection, supported by automatic conversion
procedures and data-driven linguistic analyzers, with a minimum of manual
validation. In this way, we hope to be able to create a large-scale, high-quality
Swedish treebank, a resource that is badly needed for research and development in language technology, as well as for empirical linguistic research.
References
Ahrenberg, L. (2007). LinES: An English-Swedish parallel treebank. In
Proceedings of the 16th Nordic Conference of Computational Linguistics
(NODALIDA), pp. 270–273.
Brants, T. (2000). TnT – a statistical part-of-speech tagger. In Proceedings of
the 6th Conference on Applied Natural Language Processing (ANLP).
Carlberger, J. and V. Kann (1999). Implementing an efficient part-of-speech
tagger. Software Practice and Experience 29, 815–832.
Einarsson, J. (1976a). Talbankens skriftspråkskonkordans. Lund University,
Department of Scandinavian Languages.
Einarsson, J. (1976b). Talbankens talspråkskonkordans. Lund University, Department of Scandinavian Languages.
Ejerhed, E. and G. Källgren (1997). Stockholm Umeå Corpus. Version 1.0.
Produced by Department of Linguistics, Umeå University and Department
of Linguistics, Stockholm University. ISBN 91-7191-348-3.
Forsbom, E. (2005). Big is beautiful: Bootstrapping a pos tagger for swedish.
Poster presentation at the GSLT retreat. Gullmarsstrand, January 27-29.
Gustafson-Čapková, S., Y. Samuelsson, and M. Volk (2007). SMULTRON (version 1.0) – The Stockholm MULtilingual parallel TReebank. http://www.ling.su.se/dali/research/ smultron/index.htm. An EnglishGerman-Swedish parallel treebank with sub-sentential alignments.
119
Hajič, J., B. Vidova Hladka, J. Panevová, E. Hajičová, P. Sgall, and P. Pajas
(2001). Prague Dependency Treebank 1.0. LDC, 2001T10.
Järborg, J. (1986). Manual för syntaggning. Technical report, Göteborg University, Department of Swedish.
Kokkinakis, D. (2006). Towards a swedish medical treebank. In J. Hajič
and J. Nivre (Eds.), Proceedings of the Fifth Workshop on Treebanks and
Linguistic Theories, pp. 199–210.
Marcus, M. P., B. Santorini, and M. A. Marcinkiewicz (1993). Building a large
annotated corpus of English: The Penn Treebank. Computational Linguistics 19, 313–330.
Megyesi, B. (2002). Data-Driven Syntactic Analysis: Methods and Applications for Swedish. Ph. D. thesis, KTH: Department of Speech, Music and
Hearing.
Nilsson, J., J. Hall, and J. Nivre (2005). MAMBA meets TIGER: Reconstructing a Swedish treebank from Antiquity. In P. J. Henrichsen (Ed.), Proceedings of the NODALIDA Special Session on Treebanks.
Nivre, J. (2000). Sparse data and smoothing in statistical part-of-speech tagging. Journal of Quantitative Linguistics 7, 1–17.
Nivre, J., J. Hall, and J. Nilsson (2006). Maltparser: A data-driven parsergenerator for dependency parsing. In Proceedings of the 5th International
Conference on Language Resources and Evaluation (LREC), pp. 2216–
2219.
Nivre, J., J. Nilsson, and J. Hall (2006). Talbanken05: A swedish treebank
with phrase structure and dependency annotation. In Proceedings of the 5th
International Conference on Language Resources and Evaluation (LREC),
pp. 1392–1395.
Teleman, U. (1974). Manual för grammatisk beskrivning av talad och skriven
svenska. Studentlitteratur.
120
Oversettelsesassistenten
Torbjørn Nordgård
LingIT AS and NTNU
Norway
1
Introduction
In Norway, as in many other small language communities, there is a shortage
of high quality bilingual corpus data. Thus it is hard to make use of standard
Statistical Machine Translation (SMT) techniques. So, in this paper we will
discuss scalability and domain adaptation for an experimental machine
translation system that is easy to assemble and which requires standard and
generally available machine-readable linguistic data. The system, called
Oversettelsesassistenten (The Translation Assistant), henceforth OA, was
developed at NTNU in 2005 - 2007 as a prototype that makes use of readily
available resources like monolingual full form word lists, machine readable
lexicographic dictionaries, POS taggers, finite state automata and
monolingual corpora. OA has already been used as a reference system in the
evaluation of the LOGON system (see Oepen et al, 2004).1
2
OA Components
Oversettelsesassistenten contains the following components, ordered
sequentially as displayed in the figure:
POS Tagger Finite State Transducer Decoder
The components are described below, but first we give an overview of the
linguistic resources used. Source language full forms are taken from
NorKompLeks (Nordgård, 2000), target language full forms are extracted
from the English section of Multext (Ide and Véronis, 1994), target language
corpus is the NYT sections of English Gigaword. Translation
correspondences were extracted from Engelsk stor ordbok (Henriksen et.al.,
2001). These resources have been automatically prepared in order to obtain
full form correspondences from Norwegian to English. The resulting
resources have not been inspected thus far, except for grammatical tag
correlations between the various sources.
1
This work was done while I worked at NTNU, partly together with Ola Huseth.
121
2.1 POS Tagger
The tagger has a trigram HMM engine with a Viterbi decoder and linear
interpolation between n-gram models. It has as suffix guessing facility for
unknown words, in addition to intuitive and simple “tricks” for recognition
of proper nouns and numbers. The tagset comprises 44 tags in total. The
training data set is quite small; 101488 words and 5551 sentences. The data
is collected from Norwegian newspapers, and it is annotated by students
from NTNU. Tagging accuracy is 95%.
An example from the tagger in operation: The transition path for the
observation sequence “Jeg synes at tagging er morsomt.” is
pron
verb_pres
subj
noun_sg_indef
verb_pres
adj_pos
EOS
pronoun
verb in present tense
“subjunction”, i.e., complementizer
noun, singular and indefinite form
verb in present tense
adjective in positive degree
end of sentence
which gives the tagging result
Jeg<pron>
synes<verb_pres>
at<subj>
tagging<noun_sg_indef>
er<verb_pres>
morsomt<adj_pos>
.<EOS>
The tagset is adapted to the goal of the system, i.e., translation from
Norwegian to English. This is why morphological features like gender are
absent in the tagging result.
2.2 Finite State Transducer
When the tagger has finished its work, the result is passed to a Finite State
Transducer (FST). The objective of the FST is to prepare the source string
for the decoder by performing actions like
•
insertion of grammatical words (e.g.; the)
•
enforcing “do-support”
•
possessive fronting (e.g.; katten min min katt)
122
•
perform “safe” initial translations of phrases (e.g.; i morgen tomorrow)
The general idea of preparing source language patterns for translation into
the target language is well-known in the MT field. Even though the method
has limitations it is nonetheless an efficient and powerful strategy as long as
it is used with care.
In OA the transduction is implemented as Prolog DCG rules. The DCG
formalism by itself is far more powerful than finite state grammars, but all of
the defined transducer rules are within what FST machines are able to do.
Crucially, the DCG formalism makes it easy to formulate linear recursive
deterministic phrase scanning when the input sequence is a POS tagged
expression. Consider the following input sequence to the transducer:
tg(['XSTARTX', 'Han':'pron',
'beundrer':'verb_pres', 'ikke':'adv',
'danskene':'nun_pl_def','.':'EOS']).
The pronoun “Han” is unambiguously third person singular, and it is
immediately followed by a verb in the present tense and an adverb. In
English this syntactic configuration requires do-support. The object NP
danskene is in the definite form, which should be preceded by the definite
article in the target language. From this information the transducer is able to
produce
[XSTARTX, han:pron, does:_, ikke:adv,
beundrer:vform=inf, the:_,
danskene:noun_pl_def, .:EOS]
That is, do-support with the third person singular form of the verb (does), a
restriction on the form of the main verb beundrer (the translation of liker
must be in the infinitival form), and insertion of the in front of the definite
NP danskene. These modifications of the input are the results from the
operations of two FST rules. The output of the tagger is then given to the
translation decoder (see next section).
In short, the job of the transducer is to adjust the input prior to the general
lexical translation operations.
2.3 Translation Decoder
The translation decoder has the general properties of a standard HMM
engine. The observation sequence is the output from the FST described
above. The transitions are the set of possible translations that are compatible
with the elements of the observation elements.
Since the availability of bilingual language corpora is very limited,
translation probabilities on the word and phrase level are approximated on
123
data from a small bilingual corpus so that dictionary defined base form
correspondences are counted. The probabilities are evenly distributed over
the entire inflection paradigms. The effect of this strategy is that we have
some indications of a prior probability that can be used (i.e., translation
correspondences that are attested). It is better than nothing, but if a larger
amount of bilingual data becomes available, the prior selection of translation
candidates will be far more reliable. Luckily, there are quite a lot of
available English text data. Thus, n-grams calculated from the language
model play a very significant role in the system.
When the decoding table is filled, the bilingual full form lexicon is
consulted. If no restriction is placed on a source item, all translation
possibilities are added to the network. If there are restrictions present (as
vform=inf, see above), target language items that adhere to the restrictions
are selected. If a target language item has been selected by the transducer
(for instance the:_, cf above), it will be the only element at that position in
the network.
Since we are using a trigram language model the states in the network are
pairs of items from the target language (technically, one element of a pair
might be a multiword element, but we leave those issues aside here). The
most relevant parts of the decoding table for the translation of the Norwegian
sentence Noen studenter skrev en interessant artikkel is provided below. By
following the back pointers from the best final state in the network (i.e.,
story.), the reader can confirm that the best translation is Some students
wrote an interesting story.
0 XSTARTX any -13.89 BP: -1
0 XSTARTX anybody -20.22 BP: -1
0 XSTARTX anyone -17.60 BP: -1
0 XSTARTX anything -16.53 BP: -1
0 XSTARTX some -12.70 BP: -1
0 XSTARTX something -15.33 BP: -1
1 any students -37.47 BP: START any
1 anybody students -60.74 BP: START anybody
1 anyone students -52.89 BP: START anyone
1 anything students -49.69 BP: START anything
1 some students -32.14 BP: START some
1 something students -46.08 BP: START something
2 students scribbled -58.04 BP: some students
2 students typed -60.34 BP: some students
2 students wrote -46.96 BP: some students
3 scribbled a -78.42 BP: students scribbled
3 scribbled about -103.86 BP: students scribbled
3 scribbled an -103.038 BP: students scribbled
3 scribbled one -102.80 BP: students scribbled
3 typed a -81.78 BP: students typed
3 typed an -83.98 BP: students typed
3 typed one -81.95 BP: students typed
124
3 wrote a -57.66 BP: students wrote
3 wrote an -59.50 BP: students wrote
3 wrote one -60.38 BP: students wrote
4 a interesting -66.91 BP: wrote a
4 an interesting -69.80 BP: wrote an
4 one interesting -75.67 BP: wrote one
5 interesting article -74.49 BP: an interesting
5 interesting clause -94.96 BP: a interesting
5 interesting item -95.47 BP: a interesting
5 interesting piece -77.97 BP: an interesting
5 interesting product -79.79 BP: an interesting
5 interesting section -86.02 BP: a interesting
5 interesting story -76.16 BP: an interesting
6 article . -135.27 BP: interesting article
6 clause . -170.19 BP: interesting clause
6 item . -170.70 BP: interesting item
6 piece . -138.73 BP: interesting piece
6 product . -143.54 BP: interesting product
6 section . -149.76 BP: interesting section
6 story . -105.03 BP: interesting story
Note that locally “wrote a”, “a interesting” and “interesting article” have
better values than “wrote an”, “an interesting” and “interesting story”, but
the latter alternatives are chosen during back pointer traversal. This
phenomenon is a well-known property of HMMs.
The current system is limited to n-gram size 3. It is reasonable to assume
that if the n-gram size is increased translation quality will increase as well,
provided the amount of training data is sufficient. We leave this issue to
future versions of OA.
3
Domain Adaptation
From the LOGON project there are some Norwegian - English corpus data
available: training and test data with reference translations. The data is
thematically tied to mountain hiking. In the experiment we have used three
distinct Norwegian English corpora:
•
LOGON's initial small training data (the Tur corpus), consisting of
104 Norwegian source sentences and three English reference
translations for each sentence.
•
LOGON's main training corpus (the Jotunheimen corpus), which has
2146 Norwegian sentences with three reference translations each.
•
One of LOGON's test corpora (the Jotunheimen test set, unknown
vocabulary part), containing 92 test sentences and three reference
125
translations. The notion “unknown vocabulary” is irrelevant for our
purposes since the test data is completely unknown to the OA system,
and no operations are made in order to prepare the system for this
particular test data set.
3.1 Tur Adaptation
First we adapt the system to the small initial training data by using lexical
FST rules, but initially we test the system with no adaptations to the Tur data
set. Then we modify the target language model by including reference
translations from the Jotunheimen corpus (the source sentences in Tur and
Jotunheimen are not overlapping). In the next experiment we use FST rules
derived from properties of the test document, but language models are not
“boosted” by domain sentences as in the second experiment. And finally, we
include both new rules and target domain adaptation. The results are as
follows:
•
No rules based on the training document, no domain n-grams: BLEU
SCORE: 0.3141
•
No domain rules, domain n-grams from the Jotunheimen Corpus:
BLEU SCORE: 0.3627
•
With rules based on the training document, no domain n-grams: BLEU
SCORE: 0.4498
•
With rules based on the training document, domain n-grams from the
Jotunheimen Corpus: BLEU SCORE: 0.5221
If we take the first experiment as baseline, we observe a 15% increase in
BLEU score when domain n-grams are included. Rule adaptations give a
very clear effect: 43% increase in BLEU score, and the combination of these
results in an increase of 66%. The resulting BLEU score is quite respectable.
The effects of both strategies provide very nice BLEU score increase, but the
rules based on this particular corpus is of course methodologically dubious
with respect to general capability of the system when it is confronted with
data from other sources, as we will see below.
3.2 Jotunheimen Training Data
In the next experiment we perform three tests on the Jotunheimen data set.
The first test is not optimized by any of the two strategies, the second makes
use of the rules made on the basis of Tur, and the third uses n-grams from
the Jotunheimen data set itself:
126
•
No rules based on the Tur data set, no domain n-grams: BLEU
SCORE: 0.3146
•
With rules based on the Tur data set, no domain n-grams: BLEU
SCORE: 0.3181
•
With rules based on the Tur data set, domain n-grams from the
Jotunheimen Corpus: BLEU SCORE: 0.3795
Note that the effect of the Tur rules is hardly recognizable, but the effect of
n-grams from the same test set is obvious, i.e., an increase of 20%. The
reason why the Tur rules has so limited effect must be attributed to the fact
that these rules are very lexically dependent, and they only have effect when
exact triggering strings are observed in the source tagging sequence.
3.3 Jotunheimen Test Data
Let us now go into one of the held-out sections of the Jotunheimen data set.
Note at the outset that this appears to be much “easier” sentences than those
in the training set since the baseline BLEU score is much better here
(0.3685, see below). We observe the same insignificant effect of the Tur
rules (0.3692). Addition of domain dependent n-grams appears to be far
more important, i.e., a BLEU score increase of 10%. This effect is however
not as clear as when the n-gram models are derived from the same data set
(as in the Jotunheimen training data test in the previous pragraph), as one
can expect.
•
No rules based on the Tur data set, no domain n-grams: BLEU
SCORE: 0.3685
•
With rules based on the Tur data set, no domain n-grams: BLEU
SCORE: 0.3692
•
With rules based on the Tur data set, domain n-grams from the
Jotunheimen training corpus: BLEU SCORE: 0.4127
One might wonder why the testing on unseen data gives better results than
testing on training data. The answer is simply that the test data accidentally
contains a higher proportion of one and two-word sequences than the
training data, see Johannessen, Nordgård and Nygaard (in preparation) for
details. To sum up thus far, domain n-gram adaptation appears to be very
effective when OA is to be fine-tuned with respect to some limited domain.
127
3.4 Domain N-gram Boosting
When domain dependent n-grams are added to the training data, it is
interesting to figure out the optimal “boost” level. In all the experiments
hitherto the boost factor is 2000, which means that each domain n-gram is
multiplied by 2000. No n-grams have been removed. In the table below
various boost levels are used when the system has translated sentences from
the Jotunheimen test set.
Boost: 1
Boost: 10
Boost: 100
Boost: 1000
Boost: 2000
Boost: 4000
Boost: 6000
Boost: 8000
Boost: 10000
Boost: 14000
BLEU SCORE: 0.3375
BLEU SCORE: 0.3564
BLEU SCORE: 0.3876
BLEU SCORE: 0.4086
BLEU SCORE: 0.4127
BLEU SCORE: 0.4145
BLEU SCORE: 0.4182
BLEU SCORE: 0.4181
BLEU SCORE: 0.4200
BLEU SCORE: 0.4200
These results clearly show that some form of boosting should be done.
Curiously, a low boost gives worse results than no boost. For the present
experiments it seems that something around 10,000 is the best boost factor
we can get.
4
Conclusions
In this paper, we have outlined the architecture of Oversettelsesassistenten,
which is a system based on well-known techniques (HMM-based POStagging, finite state transduction, HMM-based decoding applied to
translations models) put together in a hybrid system which requires little
training data in the form of aligned bilingual corpora. The system does
require monolingual full form word lists and corpora for the target language,
in addition to a standard bilingual dictionary which has to be synchronized to
the monolingual word lists.
We have seen that rules specially designed for certain corpora can boost
translation quality in terms of BLEU scores, but this approach does not
generalize properly to other texts from the same domain. N-gram boosting
has a very positive effect, however, and this approach generalize to certain
limits, which probably varies from case to case. We believe that the OA
approach can be used in MT system design when the relevant resources are
available, and, crucially, when high quality aligned bilingual corpora are
absent.
128
References
Henriksen, P., V. C. D. Haslerud og Ø. Eek. (2001). Engelsk stor ordbok –
Engelsk-norsk / Norsk-engelsk. 1 edition, Kunnskapsforlaget, Oslo.
Ide, N. and J. Véronis. (1994). MULTEXT: Multilingual Text Tools and
Corpora. In Proceedings of the 15th International Conference on
Computational Linguistics, COLING 1994, Kyoto, Japan.
Johannessen, J. B., T. Nordgård and L. Nygaard (in preparation). Evaluation
of the LOGON demonstrator. Manuscript in preparation for LOGON
monograph.
Oepen, S., H. Dyvik, J. T. Lønning, E. Velldal, D. Beermann, J. Carroll, D.
Flickinger, L. Hellan, J. B. Johannessen, P. Meurer, T. Nordgård and V.
Rosén. (2004). Som å kapp-ete med trollet? Towards MRS-based
Norwegian-English machine translation. In Proceedings of the 10th
International Conference on Theoretical and Methodological Issues in
Machine Translation, Baltimore, MD.
Nordgård, T. (2000). NORKOMPLEKS - A Norwegian Computational
Lexicon. In Proceedings of COMLEX 2000. Workshop on Computational
Lexicography and Multimedia Dictionaries. Wire Communications
Laboratory, University of Patras, Greece.
129
How Predictable is Finnish Morphology? An
Experiment in Lexicon Construction
Aarne Ranta
Chalmers University of Technology and University of Gothenburg
Department of Computer Science and Engineering
1
Introduction
A Finnish noun has hundreds of forms, and a Finnish verb has thousands. The
classification of the ways of forming them in Nykysuomen Sanakirja (“Dictionary of Contemporary Finnish”, NSSK, Sadeniemi, 1961) gives 82 paradigms
for nouns and 45 for verbs. At the same time, Finnish is not only complex but
extremely regular: fluent speakers can identify the correct paradigm of a new
word by just seeing one or two forms.
In this paper, we will first set up a framework of computational morphology
using smart paradigms, heuristic functions that take just one or a few forms
of a word as their arguments and infer the complete inflection table of the word
from them. Then we present an implementation of Finnish smart paradigms,
and relate them to traditional NSSK-style paradigms. We evaluate the access
functions by counting the number of incorrect inferences in different kinds of
word lists. From this, we can estimate the average number of forms needed
to infer the correct inflection of a Finnish word. We also present a bootstrapping method for large-scale lexicon building, where the number of forms is
increased in successive iterations.
2
Morphological Lexicon
A morphological lexicon is a list of words with all their inflectional forms.
To take a simple example, an English morphological lexicon might have the
following kinds of entries:
00123 N house houses house’s houses’
00456 V house houses housed housed housing
10871 V write writes wrote written writing
Each entry has a unique identifier (here an integer), a part-of speech tag (here
N or V), and a complete list of forms.
130
A morphological lexicon can be seen as the canonical form of the description of the words of a language. This means that it explicitly gives all the data
that is needed to produce and recognize all forms and all words. It does not
mean that anyone ever has to write the lexicon explicitly, or store it in its full
form. To write a lexicon, an efficient way can be to use regular expressions
(Beesley and Karttunen, 2003) or paradigm functions (Huet, 2005; Forsberg,
2007). To store a lexicon, finite-state transducers are a compact format, which
avoids replicating common parts of words. Finally, also to apply a lexicon,
finite-state transducers are adequate, for both analysis (finding the descriptions
of a given form) and synthesis (finding the forms matching a given description).
Transducers are the essence of finite-state morphology, which moreover
uses regular expressions as source code for the morphology. However, using
transducers at runtime is independent of the source format: a morphological
lexicon in canonical form, what ever way it is produced, can be easily compiled
to a transducer. In the following, we will use the word and paradigm model
(Hockett, 1954) when defining morphology. To add a word to a lexicon in this
model, a word and a paradigm are given; the paradigm is a function that from
the word produces a complete list of its forms, which can be added as an entry
to a morphological lexicon and/or used for extending a transducer with more
edges and states.
3
What Is a Paradigm?
Paradigm is not a mathematically precise notion like finite-state transducer
is. We can, however, easily build a mathematical characterization by asking
ourselves what a paradigm is supposed to do. We start with an inflection
table: it is a function from form descriptions (tags of a given tag set) to actual
forms (strings). A part of speech is morphologically defined in terms of what
forms there are in its inflection table. For example, English nouns are inflected
for both number and case, and a noun inflection table is thus a function of type
Number * Case -> Str
i.e., a function from the cartesian producs of numbers and cases to strings. The
notation we use is from GF (Grammatical Framework, Ranta, 2004). English
verbs have a different type,
VForm -> Str
where the verb form type VForm comprises possible verb forms: infinitive,
third person singular present, past indicative, past participle, and present participle. If the verb be is included, some more forms are needed.
A paradigm, then, is a function that builds an inflection table from a given
word form. Thus an English noun paradigm is a function of type
131
Str -> (Number * Case -> Str)
For instance, the regular noun paradigm
regNoun : Str -> (Number * Case -> Str)
could be defined as the function that adds the endings Ø, s, ’s, and s’ to a given
nominative singular form to produce all the four forms. The form serving as
the argument of a paradigm coincides in this case with the stem, where the
stem is defined as an immutable prefix to which endings are glued.
So, how many noun paradigms are there in English? If we require the arguments of paradigms to be immutable stems, we end up with a high number of
paradigms, including
• fully regular nouns, such as house, where the stem is the nominative
singular form
• nouns ending with a y (preceded by a consonant), such as fly, where the
stem is fl
• some nouns ending with ouse, such as mouse, where the stem is m
This definition of paradigms was consistently carried out in Swedish by
Hellberg (1978), who ended up with hundreds of paradigms. He called the
immutable prefix the technical stem. In traditional linguistics, the notion of a
stem is more abstract. Paradigms may permit stem alternations, so that e.g.,
English fly is considered regular with the alternation of y to ie before the plural s. Paradigms may also permit multiple stems: the verb form series drink,
drinks, drank, drunk, drinking is generated from the three stems drink, drank,
drunk rather than from the technical stem dr. Yet another way to see this case
is in terms of a stem drVnk with a place holder V for a vowel, which undergoes
the thematic vowel alternation i-a-u.
What is the most intuitive way of presenting paradigms, if they are to be used
by lexicographers who are not linguists? We can take a cue from dictionaries.
The technique of paradigm identifiers (usually numbers) is sometimes used.
Thus Le Petit Robert of French has
concevoir v.tr. <28>
An alternative would be to give a few forms that identify the paradigm:
concevoir v.tr. conçois, concevons, conçoive,
concevrai, conçu
This idea is related to the technique of multiple stems in linguistics, with the
difference that the stems need not really be independent of each other; the idea
of a thematic series is just that the series gives enough information to determine
all forms of the word.
132
4
Smart Paradigms
Thematic form lists are often used with a variable number of arguments: for
instance, if a verb is completely regular, only one form is given. We will call a
thematic list with just the necessary number of terms a smart paradigm. We
have found smart paradigms to be an intuitive and efficient way of building
lexica in practice. The smart paradigm is a set of functions that take one or
more arguments, and the user (who is able to recognize current inflection even
if not predict it) can start with one argument, see what it generates, and give
more forms if necessary.
The programmer’s variant of a smart paradigm is a set of construction functions—functions with an increasing number of argument lists and an inflection
table as value. Given that we define the type V as the type of inflection tables
with all verb forms in English, we can present the verb construction function
as the following group of functions:
mkV_1
mkV_2
mkV_3
mkV_5
:
:
:
:
(talk : Str) -> V
(omit,omitted : Str) -> V
(drink,drank,drunk : Str) -> V
(go,goes,went,gone,going : Str) -> V
The identifiers talk, omit, etc., are variables, which all have the type string.
Their names suggest to the user what form is expected for each variable, which
is a part of the documentation of the paradigm. For GF itself, they make no
semantic difference. The type of mkV_2, for instance, is just the same as
Str -> Str -> V
i.e., a function that takes two strings to a verb.
An alternative representation of the above set of construction functions is a
web form with five slots. Depending on how many slots are filled, some of the
mkV functions is applied, and the full inflection table is displayed to the user.
If she is satisfied with the result, she can push the “Save” button to extend the
lexicon; otherwise, she can add more forms until the table is correct.
The GF Resource Grammar Library (Ranta, 2008) is an implementation of
the morphology and a part of the syntax of 13 languages in the GF grammar formalism (Ranta, 2004). The morphology implementations provide smart
paradigms for 9 of the languages included: Danish, English, Finnish, French,
German, Italian, Norwegian, Spanish, and Swedish (Arabic, Catalan, Russian,
and Urdu do not yet have smart paradigms at the moment of writing). The
presentation of the paradigms looks exactly as above. Effort has been spent to
make the paradigms smart also in the sense of requiring a minimum of forms.
For instance, the one-place noun paradigm for English inspects the singular
form of the word to select the proper plural form in a wide variety of cases.
mkN_1 : (word : Str) -> N = \word ->
133
let
words : Str = case word of {
_ + ("a"|"e"|"i"|"o"|"y") + "o" => word + "s" ;
_ + ("s"|"x"|"sh"|"o")
=> word + "es" ;
_ + ("a"|"e"|"o"|"u") + "y"
=> word + "s" ;
x + "y"
=> x + "ies" ;
_
=> word + "s"
}
in
mkN_2 word words
The function uses regular expressions to inspect the suffix of the word. The
plural created is sent, together with the singular, to the 2-argument mkN function. Actual use of the 2-argument variant is needed only for truly irregular
nouns, such as mouse or man.
A few words on GF notation might be in place. The above piece of code defines a function called mkN_1. The definition consists of a type and a definining expression. The type here is a function from Str to N. The definition is a
lambda term binding the variable word. For this variable, mkN_1 returns the
value of calling mkN_2 with two arguments: word itself and words, which
is defined locally in a “let” expression. The definition of the local constant
words makes a case analysis of the string bound to the variable word. The
cases are tried in the order in which they appear. The first case splits the string
into three parts: any prefix (matched by the wild card _), followed by any of
the strings a, e, i, o, y, terminated by the string o. This case matches strings
such as bamboo and embryo, which get the plural ending s attached to the stem.
Other words ending with an o are passed to the next case, which uses the same
ending es as it also assigns to words ending with s-like sounds. Words ending
with a y are treated next. The last case uses a catch-all pattern, giving a default
s plural to all words that were not matched before.
5
The Inflection of Nouns in Finnish
We shall now finally enter Finnish morphology. We go through the inflection
of nouns in more detail than verbs: even though verbs have more forms, they
are more uniform and regular: NSSK has 82 paradigms for nouns and 45 for
verbs.
A noun form has several components: stem, case, number, possessive, and
optional particles. Here is an example:
ves +
i +
ssä +
"water" Plural Inessive
"also in my waters"
ni +
Possessive Sg_1
kin
"also"
With all possible combinations of the components, the number of different
forms can be estimated to be around 1,500. In practice, grammar books only
134
nominative
genitive
partitive
essive
translative
inessive
elative
illative
adessive
ablative
allative
abessive
comitative
instructive
singular
vesi
veden
vettä
vetenä
vedeksi
vedessä
vedestä
veteen
vedellä
vedeltä
vedelle
vedettä
-
plural
vedet
vesien
vesiä
vesinä
vesiksi
vesissä
vesistä
vesiin
vesillä
vesiltä
vesille
vesittä
vesine
vesin
meaning
“water(s)”
“of water(s)”
“portion of water(s)”
“as water(s)”
“to as water(s)”
“in water(s)”
“from in water(s)”
“to in water(s)”
“on water(s)”
“from on water(s)”
“to on water(s)”
“without water(s)”
“with water(s)”
“by means of water(s)”
Figure 1: The inflection table of a Finnish noun.
need to consider around 30 forms, since the possessives and particles are (almost) purely agglutinative. The 2 numbers and 14 cases specify the core of the
paradigms, where the case and the number often form portmanteau fusions,
and the stem may change in function of the ending. In two of the cases, no
number distinction is made, and we thus end up with 26 noun forms, as shown
in the inflection table in figure 1.
Many of the 26 noun forms can be obtained from each other by just changing an ending. For instance, five of the singular local cases (inessive, elative,
adessive, ablative, abessive) form a group where just the ending needs to be
interchanged. NSSK uses 8 forms as determining the others. In the GF implementation, we have used 10 arguments in the worst-case noun constructor.
These 10 forms are guaranteed to cover all stem and vowel alternations that a
Finnish noun can undergo, so that all the 26 paradigm forms (and thereby the
1,500 full forms) can be generated by deterministic concatenative procedures.
These ten forms are printed in boldface in figure 1.
As partly shown in the inflection table of vesi, Finnish words are subject to
the following kind of alternations:
• Vowel harmony: the ä in endings is realized as a, if the stem contains
one of the letters a, o, u.
• Consonant gradation: many consonants and consonant clusters have a
strong and a weak grade, which are selected as a function of the ending;
in the vesi example, d is the weak grade of t.
135
• Stem vowel alternation the last vowel of the stem varies as a function
of the ending; in the vesi example, i alternates with e.
In the NSSK paradigm set, vowel harmony and consonant gradation are
treated separately from the paradigms. Thus, for instance, “Paradigm 1” (valo,
“light”) has at least 30 variants, if the effects of vowel harmony and consonant
gradation are built in to reach the “technical stem” notion of a paradigm. Thus
the 82 noun paradigms of NSSK involve a certain amount of abstraction, and
their user therefore has to know how to apply the vowel harmony and consonant gradation rules.
The sheer number 82, together with the complex sound alternations required, makes the NSSK paradigm system tedious and error-prone to use. In
GF, we have relieved this burden by using smart paradigms, where the user
gives a number of characteristic forms and the program identifies the paradigm
to which the word belongs. The following five constructors are currently used:
mkN_1
mkN_2
mkN_3
mkN_4
mkN_10
: (talo : Str) -> N
: (talo,taloja : Str) -> N
: (talo,taloja,talon : Str) -> N
: (talo,taloja,talon,taloa : Str) -> N
: (talo,talon,taloa,talona,taloon,talojen,
taloja,taloina,taloissa,taloihin : Str) -> N
The worst-case variant uses 10 forms, which give full certainty. The shorter
variants use 1, 2, 3, or 4 forms, with increasing certainty. In practice, the 10form variant is needed only for a small number of words, which either belong
to obsolete paradigms or have become irregular via “wear” in use.
In addition to the above paradigms, there are two more used for the formation of compound nouns:
mkN : (pika : Str) -> (juna -> N) -> N
mkN : (oma : N)
-> (tunto -> N) -> N
The first case covers the most common type of compounds, where an immutable prefix is added to an inflectible noun. In the second type, both parts of
the compound are inflected in agreement. In the selection of a paradigm, it is
crucial to know what the last part of a compound is, in order to get the vowel
harmony right and, in some cases, to decide how many syllables the word has.
Given the above system of paradigms—which will be explained in more detail in later sections—one can build a user-friendly lexicon construction system
as follows. First of all, an irregularity lexicon is created to make the use of
the 10-place constructor unnecessary. When encountering a new word, we first
check if it is included in the irregularity lexicon. If not, we try to define it with
the 1-place noun constructor. If this fails (in human inspection), we give yet
another form, and so on. This defines a smooth process in which, with very
little training, a lexicographer can treat hundreds of nouns in an hour.
136
The interesting question is now: how smooth is the procedure of adding
characteristic forms—how many forms are needed in average? In other words:
how predictable is Finnish inflection? We shall now go on to present an experiment that gives us some figures. After that, we will take a look at the
definitions of the constructors and the paradigms underlying them; this inspection will both explain the figures and give a hint on what kinds of words will
typically need more forms to inflect correctly.
6
A Noun Prediction Experiment
The first experiment was carried out with written Finnish from four different
genres, treating each genre in the same way. Four samples of equal size were
gathered, from the following sources:
• Aino, a children’s book by Kristiina Louhi (1989)
• Duodecim, a professional article within clinical medicine (2007)
• Swadesh, the list of the 207 “most primitive words” proposed by Swadesh
(1955)
• Dictionary, a medium-size Finnish-English dictionary (1971)
From each source, a random sample of 99 distinct nouns were collected. In
Aino and Duodecim, we took the first nouns occurring in the text. In Swadesh,
we took all nouns and enough many random adjectives to reach the desired
number (adjectives in Finnish are inflected in the same way as nouns). In
Dictionary, we took the first noun of every fifth page. In all cases, compound
nouns were eliminated by only considering their last parts; it is impossible to
predict the inflection of a compound without identifying its last part, and this
is not a mechanical task in general.
The random sample of nouns was presented as a list of their nominative
singular forms:
Aino
tunti
äiti
tähti
puhelin
kuuloke
From this list we create a gold standard listing all the 10 thematic forms of
each noun:
Aino Ainon Ainoa Ainona Ainoon
Ainojen Ainoja Ainoina Ainoissa Ainoihin
137
tunti tunnin tuntia tuntina tuntiin
tuntien tunteja tunteina tunneissa tunteihin
äiti äidin äitiä äitinä äitiin
äitien äitejä äiteinä äideissä äiteihin
tähti tähden tähteä tähtenä tähteen
tähtien tähtiä tähtinä tähdissä tähtiin
puhelin puhelimen puhelinta puhelimena puhelimeen
puhelimien puhelimia puhelimina puhelimissa
puhelimiin
kuuloke kuulokkeen kuuloketta kuulokkeena
kuulokkeeseen kuulokkeiden kuulokkeita kuulokkeina
kuulokkeissa kuulokkeisiin
The gold standard was created using the bootstrapping method of section 9,
manually verified.
In the experiment, the outcomes of the 1-place, 2-place, 3-place, and 4place noun constructors were compared with the gold standard. From each
comparison, the number of nouns whose inflection is incorrect (w.r.t. the gold
standard) was counted. The constructors are designed to be monotonic, so that
giving more arguments never destroys a correct inflection. This means that the
number of errors decreased as the number of arguments increased.
Different kinds of material were expected to give different degrees predictability. We expected Duodecim to contain mostly new and technical words,
which would thereby be regular; this would be a comforting result concerning
the main purpose of GF, which is to build translation and generation systems
for technical domains. We expected Swadesh and Aino to contain many old,
worn, irregular words, and Dictionary to give a reasonable average. The results
of the experiment, covered in the following table, show that our expectations
were only partly satisfied:
args
1
2
3
4
Aino
8
1
0
0
Duodecim
16
6
3
1
Swadesh
31
15
7
2
Dictionary
19
4
2
1
The slightly surprising outcome was that Aino was the easiest material to
predict. Duodecim is close to Dictionary, whereas Swadesh is rich in the words
of type vesi-veden (“water”), which is an ancient paradigm no longer productive. The altogether 3 unpredicted words all represent irregular paradigms intentionally left outside the heuristics: kevät (“spring”), mies (“man”), sydän
(“heart”).
As a preliminary conclusion for general text we could thus say:
• For 80% of nouns, the inflection is correctly inferred from just one form
(the nominative singular).
138
• For 90% of words, it is enough to have one more form (the partitive
plural).
• Adding the genitive and partitive singular gets all nouns right, except for
a fixed set of nouns that can be given in advance.
7
A Large-Scale Noun Prediction Experiment
The noun prediction experiment with different genres completed, we got hold
of a freely available electronic word list (KOTUS, Kotimaisten Kielten Tutkimuskeskus, 2006) named after its provider Kotimaisten kielten tutkimuskeskus
(“Research Centre for Domestic Languages”). KOTUS has 50 noun paradigms,
which are used for annotating the lemmas in the word list. We implemented
these paradigms using the 20 GF paradigms of section 10, with recourse to the
worst-case noun constructor for some rare KOTUS paradigms. Then we took
the word list and removed most compounds (those clearly enough marked)
and plurale tantum words (which our paradigms could not directly handle).
We ended up with a list of 27,680 nouns, and used the paradigm annotations
to expand this to a gold standard and repeated the experiment.
The outcome of this second experiment largely confirmed the earlier results:
args
1
2
3
4
KOTUS #
4993
1062
792
789
KOTUS %
18.0
3.8
2.9
2.9
The insignificant drop between 3 and 4 suggests that the singular partitive
should rather be treated in the irregularity lexicon.
We also tested an alternative order of forms, using the genitive singular
rather than the partitive plural as the second form. In the small experiments
above, this order gave slightly better results, especially for the Swadesh corpus. In KOTUS, however, the error rate with two forms increased to 3597, that
is, 13.0%. This result confirmed that the partitive plural is more useful than
the genitive singular in predicting inflection. The a priori reasons originally
leading to this choice are given below in section 11.
8
Predictability as the Average Number of Required
Forms
Now, how predictable is Finnish morphology? One possible answer is given
by calculating the average number of forms needed to identify the inflection
of a Finnish noun in the KOTUS list. Assuming that all words we fail to predict
139
with 3 arguments need 10 forms, we get
(792∗10+(1062−792)∗3+(4993−1062)∗2+(27680−4993))/27680 = 1.42
forms in average. Assuming that those words can be found in the irregularity
lexicon and hence only need one form, we get 1.16 forms in average. Which
of these figures should be used?
When looking at the nouns in KOTUS that we failed to predict, our earlier
expectations where partly falsified. Irregular “old” words like kevät and mies
are of course present, but the majority are new words whose orthography has
not been naturalized to match the pronunciation. A typical example is the
word brie (“brie cheese”), which has the French pronunciation [bri:], and it is
hence inflected like pii (“silicon”). But the orthography can mislead a smart
paradigm to inflect it like tie (“road”).
For a Finnish speaker, inflecting new loan words is to a large extent dependent on education. For instance, KOTUS follows the correct French pronunciation of the words calvados [kalvados] and tournedos [turnedo:] when selecting
the Finnish paradigm—but this is hardly a part of the common knowledge of
native Finnish speakers.
As a conclusion, loan words like brie, calvados, and tournedos with their
unpredictable pronunciation are a far more significant source of unpredictable
inflection than the “old” words in a static irregularity lexicon. To help future
lexicographers, the smart paradigms of the GF Resource Grammar Library
should be improved so that the full set of 10 forms are not needed as often as
now. But at this point, a prudent conclusion is to say that Finnish nouns need
1.42 forms in average.
9
A Bootstrapping Method for Lexicon
The creation of the gold standard in section 6 required manual work. Its
amount was gradually reduced in the course of the project, as we found a more
economical way of using the smart paradigms and GF. This way suggests a
general method of bootstrapping a lexicon, which would be usable for large
word lists as well, and independently of language—even though its efficiency
depends on how predictable the morphology of the language is.
The starting point in bootstrapping is a list of words in the form required
by the one-argument smart paradigm. We will use Finnish nouns as example
here, with the nominative singular as the first form:
meri
sade
nainen
kivi
rivi
140
tohtori
apina
kulkija
kukka
auto
rakkaus
To each word in this list, we apply the 1-place noun constructor, just to produce
one more form, the partitive plural:
meri
sade
nainen
kivi
rivi
tohtori
apina
kulkija
kukka
auto
rakkaus
(merejä
sateita
naisia
(kivejä
rivejä
(tohtoreja
(apinoja
(kulkijia
kukkia
autoja
rakkauksia
>> meriä)
>> kiviä)
>> tohtoreita)
>> apinoita)
>> kulkijoita)
For reasons explained in section 11, it is enough to pay attention to those nouns
that end with an i, as well as 3-syllabic nouns ending with an a or ä, to produce
a “2-form gold standard”. In the above list, five words are manually changed.
The 2-form gold standard is processed with the 2-place noun constructor,
to produce a 3-form list; now, the genitive singular is added. In this case,
we mostly have to change some 2-syllabic words that don’t have expected
consonant gradation, as well as nouns ending with us but inflected like rakkaus
(“love”) rather than pakkaus (“package”).
auto
autoja
(audon >> auton)
rakkaus rakkauksia (rakkauksen >> rakkauden)
The 3-argument noun constructor adds one more form, the partitive singular.
Some words may have to be changed, typically for words in the i-e paradigm:
meri
meriä
meren (mertä >> merta)
Actually, the number of words with a deviant partitive singular is limited, and
the last step can hence be avoided by extending the irregular lexicon with
these words—this is what we assume in the following estimate of work that
is needed.
The amount of work needed for producing a morphological lexicon can be
defined as the number of words that need to be written or read by the lexicographer: to build a lexicon with 100 lemmas, she has, in average, to
141
• check 30 partitive plural forms
• change 15 partitive plural forms
• check 50 genitive singular forms
• change 5 genitive singular forms
• change the whole inflection of 2 words (18 forms)
• altogether, read 80 forms and change 38 of these
Processing 100 words in GF to create the full set of forms (or any subset of
it) takes 0.4 seconds, so that with a suitable script (available from GF homepage) the processing part takes around 2 seconds. If changing a word form
takes 20 seconds and just reading it 5 seconds, the work spent on 100 lemmas is around 16 minutes. Thus turning a list of 3,000 noun lemmas (outside
the irregularity lexicon) into a complete morphological lexicon would take one
effective working day, plus less than 2 minutes of GF processing time.
Another estimate can be calculated from the average 1.42 forms needed to
identify the inflection of a Finnish noun (section 8 above). If 0.42 forms per
lemma have to be produced and one production takes 20 seconds, then 100
lemmas require 14 minutes. With this count, one working day is enough for
producing a lexicon of 3,480 words.
10
Basic Paradigms for Finnish Nouns
So far we have not gone into the details of Finnish inflection, but just presented
an experiment and a method, which would be applicable to other languages as
well. We will now give an outline of the inflection paradigms that we used.
The system of paradigms works in two layers:
• a user-accessible smart paradigm set mkN
• an underlying basic paradigm set close to linguistic description
The undelying basic paradigm set is reminiscent of the NSSK and KOTUS
sets, only fewer (20 instead of 82 or 50). The lower number is due to three
factors:
• higher level of abstraction
• the use of multiple arguments
• the omission of rare and obsolete paradigms (which are treated lexically
in the irregularity lexicon)
Here are the paradigms, displayed as GF type signatures:
142
dLujuus
dNainen
dPaluu
dPuu
dSuo
dKorkea
dKaunis
dLiitin
dOnneton
dUkko
dSilakka
dArpi
dRae
dPaatti
dTohtori
dPiennar
dNukke
dJalas
dUnix
dSDP
:
:
:
:
:
:
:
:
:
:
:
:
:
:
:
:
:
:
:
:
(lujuus : Str) -> N
(nainen : Str) -> N
(paluu : Str) -> N
(puu : Str) -> N
(suo : Str) -> N
(korkea : Str) -> N
(kaunis : Str) -> N
(liitin : Str) -> N
(onneton : Str) -> N
(ukko,ukon : Str) -> N
(silakka,silakan,silakoita : Str) -> N
(arpi,arven : Str) -> N
(rae,rakeen : Str) -> N
(paatti,paatin : Str) -> N
(tohtori : Str) -> N
(piennar,pientaren : Str) -> N
(nukke,nuken : Str) -> N
(jalas : Str) -> N
(unix : Str) -> N
(SDP : Str) -> N
The name of a paradigm begins with a d (for “declension”), followed by an
example word belonging to that paradigm. Some paradigms have two arguments, mainly to control consonant gradation. It is usually possible to produce the weak grade automatically from the strong grade and vice-versa, but
whether a word undergoes this gradation is a lexical property of the word. For
instance, outo (“strange”) and auto (“car”) are both inflected by dUkko, but
outo has the weak grade in the genitive oudon (and other forms demanding the
weak grade), whereas auto preserves the strong grade in auton and all other
forms. Similar examples can be found for all 2-argument paradigms, which
was what motivated the use of a second argument (an alternative would have
been to have two different paradigms).
The most complex paradigm is dSilakka, of polysyllabic words ending
with a,ä,o,ö. The rules for forming the partitive plural (the third argument)
are so complex and uncertain, that we decided to make the choice lexical (see
however Karlsson (1977), § 16, for a summary of the rules).
The last noun paradigm, dSDP, deals with acronyms recognized by a colon
between the stem and the ending: SDP:n, SDP:tä, SDP:hen. The correct ending depends on the pronunciation of the last letter as the name of a letter of the
Finnish alphabet. There are 9 different sets of endings that can result.
143
11
Smart Paradigms for Finnish Nouns
The high-level smart paradigms (the noun constructors mkN) analyse their arguments and dispatch to some of the underlying paradigms. Here is a slightly
simplified but fully functional version of the 1-argument constructor in GF
code, covering the most productive suffixes that help to select a paradigm.
mkN_1 : Str -> N = \ukko ->
let
ukon = weakGrade ukko + "n" ;
in
case ukko of {
_ + "nen" => dNainen ukko ;
_ + ("aa"|"ee"|"ii"|"oo"|"uu"|"yy"|"ää"|"öö") =>
dPuu ukko ;
_ + ("ie"|"uo"|"yö") => dSuo ukko ;
_ + ("ton"|"tön") => dOnneton ukko ;
_ + "e" => dRae ukko (strongGrade ukko + "en") ;
_ + ("a"|"o"|"u"|"y"|"ä"|"ö") => dUkko ukko ukon ;
_ + "i" => dPaatti ukko ukon ;
_ => dUnix ukko
} ;
The function uses the auxiliary functions strongGrade and weakGrade,
which implement consonant gradation. Thus consonant gradation is treated
separately from the paradigms. The same concerns vowel harmony, which
is encapsulated in a low-level auxiliary function not even visible in the code
examples of this paper.
The main cases where mkN_1 makes an uncertain guess are the following:
• all nouns ending with a short aouyäö are sent to dUkko with consonant
gradation
• all nouns ending with a short i are sent to dPaatti with consonant
gradation
• all nouns ending with a short e are sent to dRae with consonant gradation
Except for consonant gradation, the errors produced by these guesses can be
corrected by adding the partitive plural form. Hence the 2-argument constructor, again slightly simplified:
mkN_2 : (ukko,ukkoja : Str) -> N =
\ukko,ukkoja ->
let
ukon = weakGrade ukko + "n"
in case <ukko,ukkoja> of {
144
<_ + "i", _ + ("ia" | "iä")> =>
dArpi ukko (init (init ukon) + "en") ;
<_ + "i", _ + ("eita" | "eitä")> =>
dTohtori ukko ;
<_ + ("a"|"ä"|"o"|"ö"), _ + ("a"|"ä")> =>
dSilakka ukko ukon ukkoja ;
<_ + "e", _ + ("eja" | "ejä")> =>
dNukke ukko ukon ;
<_, _ + ("a" | "ä")> => mkN_2 ukko ukon ;
_ => Predef.error
(["last arg should end ’a/ä’, not"] ++ ukkoja)
} ;
The 1-argument constructor is used as a catch-all case, but it still requires the
second argument to end with an a or ä, so that it makes sense as a partitive
plural form. This guards against mistaken use of the paradigm with some other
forms.
12
Verbs
In many languages, verb morphology is more complex than noun morphology,
because verb inflection contains noun inflection as its proper part—the participle forms. Finnish is no exception, and there are actually several kinds of
participles and other “nominal forms”. At the same time, verbs are morphologically simpler than nouns, since there are fewer paradigms. NSSK has 45 verb
paradigms. The GF Resource Grammar Library has 8 “deep” paradigms, and
only the 1- and 2-argument smart constructors are exposed to lexicographers,
in addition to a worst-case 12-argument function.
We made an experiment similar to the one with nouns on the verb variants
of the 99-word Swadesh and Dictionary corpora. Here are the numbers of
erroneous predictions:
args
1
2
Swadesh
10
3
Dictionary
1
1
The unresolved verb in Dictionary is nähdä (“see”). It is also one of the 3
in Swadesh, the other ones being seistä (“stand”) and pyyhkiä (“wipe”). These
first two are deviant and belong to the irregularity lexicon, whereas pyyhkiä
would require one more form to detect consonant gradation.
The 10 verbs that come out incorrectly with mkV_1 in Swadesh are ones
with lexically defined consonant gradation, e.g., pelätä (“fear”). Its first person
singular present indicative has a strong grade consonant (pelkään), but there
are similar verbs that do not undergo consonant gradation when working out
from the infinitive form: palata - palaan.
145
The conclusion for verbs is even more encouraging than for nouns: more
that 90% can be predicted from one form, and the rest from two forms (except
for verbs in the irregularity lexicon). The problem of loan words with deviating pronunciation is largely avoided, because verbs, unlike nouns, cannot be
loaned without attaching suffixes that clearly identify the paradigm: chattailla
(“to chat on the internet”), mailata (“to send an email”). Selecting the suffix
can however still be a problem for derivational morphology.
13
Related Work
Finnish morphology has played an important role in the development of computational morphology in general, due to its high complexity combined with
a high grade of regularity. Pioneering work was carried out in the late 1970’s
by Sågvall Hein (1978, 1980), Koskenniemi (1980), and Brodda and Karlsson
(1978). Koskenniemi (1983) is generally seen as a landmark, not only because
it scaled up to a large coverage analysis and synthesis, but also because it introduced a new finite-state method known as two-level morphology, which
was later applied to a wide variety of languages. We know only few computational approaches using paradigms rather than morphophonemic processes;
Koskenniemi (1980) and Carlson (2005) are examples of ones.
As for lexicon construction, the method presented above is related to the
lexicon extraction method of Forsberg et al. (2006). The difference is that, in
that work, sets of characteristic forms are searched from a corpus of words
with unknown parts of speech, whereas in the present approach, the forms
are produced by just analysing one given form with known part of speech.
More remotely related work includes the influential algorithm for unsupervised
learning of morphology of Goldsmith (2006), in particular a further development applied to Finnish by Creutz and Lagus (2007). In these approaches,
paradigms are not given in advance: they are the very goal of the search.
14
Conclusion
In the GF Resource Grammar Library, we have built a complete system of
inflectional paradigms for nouns and verbs of Finnish (as well as 12 other
languages). Upon that system, we have implemented a set of smart paradigms,
which can be used for inferring the complete paradigm from a small set of
forms. An experiment with Finnish nouns showed that less than 1.5 forms, in
average, are needed to infer the correct inflection, with a total number of forms
between 26 and 1,500, depending on how forms are counted.
From the experiment, we have derived a general method of bootstrapping a
morphological lexicon, based on iterated addition of forms. This method can
give an efficient way to create resources for new languages. For the particular case of Finnish, much of this need has recently been catered for by the
146
release of the KOTUS word list with paradigm annotations under the GNU
LGPL license (the same as the GF Resource Grammar Library uses). Hence,
in Finnish, our method is needed only for dealing with words not included in
this word list.
References
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Brodda, B. and F. Karlsson (1978). An Experiment with Automatic Morphological Analysis of Finnish. Papers from the Institute of Linguistics, University of Stockholm, 40.
Carlson, L. (2005). Inducing a Morphological Transducer from Inflectional
Paradigms. In Inquiries into Words, Constraints and Contexts. Festschrift
for Kimmo Koskenniemi on his 60th Birthday. CSLI.
Creutz, M. and K. Lagus (2007). Unsupervised Models for Morpheme Segmentation and Morphology Learning. ACM Trans. Speech Lang. Process. 4(1), 3.
Forsberg, M. (2007). Three Tools for Language Processing: BNF Converter,
Functional Morphology, and Extract. Ph. D. thesis, Dept. of Computer Science and Engineering, Chalmers University of Technology and Gothenburg
University.
Forsberg, M., H. Hammarström, and A. Ranta (2006). Morphological Lexicon
Extraction from Raw Text Data. In T. Salakoski (Ed.), FinTAL 2006, Volume
4139 of LNCS/LNAI.
Goldsmith, J. (2006). An Algorithm for the Unsupervised Learning of Morphology. Nat. Lang. Eng. 12(4), 353–371.
Hellberg, S. (1978). The Morphology of Present-Day Swedish. Almqvist &
Wiksell.
Hockett, C. F. (1954). Two models of grammatical description. Word 10,
210–233.
Huet, G. (2005). A Functional Toolkit for Morphological and Phonological
Processing, Application to a Sanskrit Tagger. The Journal of Functional
Programming 15(4), 573–614.
Karlsson, F. (1977). Finsk grammatik. Suomalaisen Kirjallisuuden Seura.
Koskenniemi, K. (1980). On automatic lemmatization of finnish. FennoUgrica Suecana 3, 27–44.
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Koskenniemi, K. (1983). Two-Level Morphology: A General Computational
Model for Word-Form Recognition and Production. Ph. D. thesis, University
of Helsinki.
Kotimaisten Kielten Tutkimuskeskus (2006).
kaino.kotus.fi/sanat/nykysuomi.
KOTUS
Wordlist.
Ranta, A. (2004). Grammatical Framework: A Type-Theoretical Grammar
Formalism. The Journal of Functional Programming 14(2), 145–189.
Ranta,
A. (2008).
Grammatical
digitalgrammars.com/gf.
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Homepage.
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Grammar System. In COLING 78, Information Abstracts.
Sågvall Hein, A. (1980). An outline of a computer model of finnish word
recognition. Fenno-Ugrica Suecana 3, 7–26.
Sadeniemi, M. (Ed.) (1961). Nykysuomen sanakirja. WSOY.
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International Journal of American Linguistics 21, 121–137.
148
Corpora in Grammar Learning
Evaluation of ITG
1
Anju Saxena
Mikaëla Lind
Uppsala University
Department of Linguistics
and Philosophy
Katarinaskolan
Uppsala
Using Corpora in Teaching
There has been a growing interest in using natural language corpora in
teaching and in research, partly due to the growing availability of computerreadable linguistic corpora, and partly due to an increasing interest in
examining language in its natural context as opposed to investigating
constructed language examples in isolation. Researchers, teachers and
students now have access to different types of language corpora to discover
facts about language, for example about word frequency distributions in a
language or a language-type, in which context words tend to occur and
which grammatical patterns are associated with a particular linguistic item
(Ghadessy et al 2000). There have been two primary approaches to the use
of corpora in language teaching/learning:
(1) the “COBUILD approach” (or the indirect approach)
(2) the Data-Driven Learning approach (or the direct approach)
Until recently, the COBUILD approach was the predominant approach.
Corpora, in this approach, are used by researchers and producers in building
dictionaries and other language learning materials. Traditionally it has been
very large corpora which have been used for this purpose. Further, within
this approach, the user (a student, for example) receives results of a project
involving corpora as end-products (for example, in the form of a language
learning package). Learners do not get to use the corpus themselves in order
to come up with their own analyses and learn from that.
In the Data-Driven Learning approach students use corpora directly in
their own learning. They use the corpus, for example, to discover linguistic
patterns and to organize the linguistic patterns that they observe, arriving at
generalizations inductively and verifying deductive rules. Such exposure to
corpora provides students with the opportunity not only to extract relevant
examples of various linguistic structures, but also provides them with
material for discussion when they find gaps, to verify and extend their
hypotheses and to arrive at generalizations. In favor of the Data-Driven
Learning approach, Tim Johns (1991) states:
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What distinguishes the data-driven learning approach is the attempt to cut out
the middleman … and give direct access to the data so that the learner can take
part in building up his or her own profiles of meanings and uses. (Johns 1991, as
quoted in Aston 1997)
Johns (1991) divides Data-Driven Learning into three phases:
(i) observation
(ii) classification
(iii) generalization
One advantage of using corpora in teaching is that instead of learning about
linguistic theories in vacuo (a more passive learning method, where facts are
fed to students in the form of lectures and ready-made examples), students
have a chance to test these theories themselves against linguistic corpora and
thereby learn about these theories or concepts for themselves (a more active
learning method). When corpora are used by students as part of their
learning, the distinction between learning and doing research becomes
“blurred”, as the students, by a discovery procedure (thus, research), learn
things for themselves (Knowles 1990). The use of corpora in teaching can, in
this way, affect both teachers’ as well as students’ roles. This approach is as
equally relevant in a classroom set-up as in self-study situations.
The corpora used for teaching purposes may be large or small. The
purpose here is exploration and not to arrive at a water-tight description of
the phenomenon under consideration. It is possible that if small corpora are
used, the results may not be exactly the same as if the corpora were large,
but this difference does not detract from the advantages of using corpora in
teaching.
The gap between the COBUILD and DDL approaches is, however, getting
smaller. More access to corpora (especially for non-commercial purposes)
provides better conditions for their use in producing language learning tools
as well as in using them directly in teaching/learning. The aim of this paper
is to describe our experience in using corpora in grammar teaching/learning
in two Linguistics courses offered by the Department of Linguistics and
Philology at Uppsala University. The courses are Lingvistik I (Linguistics I)
and Lingvistik II (Linguistics II). We will begin by describing the web-based
platform – ITG: IT-based collaborative learning in grammar – in section 2,
followed in section 3 by an account of our experience (including student
feedback) with using ITG in these two regular courses at our university.1
1
Mikaëla Lind was responsible for the computer lab sessions where ITG was used in
the two courses discussed here. Sections 1 and 2 were written by Saxena and section 3
was written jointly by Saxena and Lind.
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2
ITG – Collaborative Learning in Grammar
ITG is a web-based platform <http://spraakbanken.gu.se/itg/itg/itg.jnlp>. Its
development began in the project “IT-based Collaborative Learning in
Grammar” which started January 1, 2002 with financial support from
Distum/Nätuniversitet in Sweden with Anju Saxena as the Principal
Investigator and the Department of Linguistics at Uppsala University as its
host. Several departments at Uppsala University as well as the Department
of Linguistics at Stockholm University and the Department of Linguistics at
the University of Gothenburg (and later on also Språkbanken, the
Department of Swedish Language at Gothenburg) were the collaborating
partners in this project. ITG is now maintained and developed further by
Språkbanken. The main aims of the project were:
• To use annotated corpora of Swedish and other languages as the basis for
learning grammatical patterns;
• To develop web-supported collaborative learning in grammar where
corpora of natural language material form the basis for group activities;
• To use the web-supported collaborative method in regular courses in
grammar at collaborating Departments of Linguistics;
• To show the wider applicability of the platform and tools developed in this
project, for example by applying them to additional languages and
additional exercise types, using ITG in other contexts;
• A significant consideration during all the stages of this project has been
that the technical aspects of using or working with the web-based
system should not increase the workload of students or faculty.
ITG has a modular architecture, composed of four types of modules (see
Figure 1, below): the encyclopedia module, the text corpus module, the
exercise module and the resource module. The encyclopedia module and the
resource module are aimed at providing information about a selected number of
relevant themes and a pool of resources for further reading. In this paper the
focus is on the Text corpus module and the Interactive exercise module.
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Figure 1: Organization of ITG
2.1 The ‘Text Corpus’ Module
The ‘Text corpus’ module contains a range of annotated corpora of Swedish and
other languages. The corpora which are accessible to an occasional visitor of
this website (category: Guest) are: the Stockholm-Umeå Corpus (SUC), ASU –
a longitudinal Swedish as second language corpus collected at Stockholm
University (spoken and written parts), the Kinnauri corpus, Sfi – the Swedish for
immigrants corpus, Skrivsyntax, ssm – Svenska som målspråk (Swedish as
target language). Most of the corpora which are used in ITG are tagged for
part of speech and lemmatized, and in some cases they are also syntactically
annotated.
The fact that these corpora were available when the project started, had its
advantages. But, it also raised issues of compatibility. A lot of effort was
spent on standardizing the corpus resources. We have been forced from the
onset to seriously discuss how to integrate existing NLP resources in our
application, as well as how to make the application itself extensible, so that
e.g. new language corpora or new annotations can be added (for details, see
Saxena and Borin 2002). Preliminary work on incorporating a Turkish corpus
in collaboration with Eva Csato has shown positive results, suggesting the
feasibility of expanding the data base of the platform with a moderate effort.
A graphic interface function has been added to the text corpus module (see
below, figure 2). With the help of this graphic interface students/researchers are
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able to see a ‘dispersion map’ of how and where one particular morpheme or
word occurs in the corpus, providing support in their work on the functions of
grammar (Olsson and Borin 2000).
Figure 1: Organization of ITG
The use of the text corpus module is not necessarily connected to the
exercise module (or to any other module). One can use the corpora available
in this module as much for teaching purposes as for one’s own research.
2.2
The ‘Interactive Exercise’ Module
The aim of the ‘Interactive exercise’ module is to provide students with means
of learning and improving their skills in grammar. This is achieved in the two
aforementioned courses in two ways: First, by means of corpus search (e.g.,
search for various lexical and grammatical elements in the corpus to find out, for
instance, frequency, position and combination, word-formation patterns). The
other use is by providing a framework for exercises on a selected theme. For
example, one theme is “syntactic function” where the computer generates at
random one example sentence from a pre-selected corpus with one or more
words underscored, forming a syntactic constituent. The task for the student is to
determine the syntactic function of this constituent (subject, object, etc.). He or
she is expected to select the correct answer from a list of potential answers. If
the answer is correct, this is shown to the user in two ways: (i) at the top of the
screen, the correct answer along with green color indicate that the answer was
correct and in the left bottom corner summary statistics of questions attempted
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and the total number of correct answers are shown. If the answer was incorrect,
the student gets immediate feedback in several ways: (i) at the top, along with
the student’s response, the correct answer appears (along with red color), (ii) in
the right-hand bottom corner the correct answer appears, and (iii) in the lefthand bottom corner summary statistics of questions attempted and the total
number of correct answers are shown (see Figure 3). The student can carry on
with her exercises as long as she wants. The exercise module is constructed in
such a way that there will not be any repeated test-sentence within 50 questions.
For pedagogical reasons, the same format is used for other themes (for example,
part of speech exercises).
Figure 1: Organization of ITG
2.3 Design principles and general philosophy of ITG
The architectural organization of ITG has several advantages, the two most
significant ones being extensibility and conceptual decentralization.
Extensibility means that new functions can easily be integrated in the
application. ‘Conceptual decentralization’ is especially significant as it
allows the possibility of adjusting to individual learning styles. For example,
if the student prefers to start out with the ‘corpus’ material (for example,
doing a corpus search for a certain grammatical element) and go from there
to the appropriate exercises (for example, part of speech exercises) when she
feels the need to do so, she has that choice. At the same time, the application
allows the possibility of starting out at other entry points, e.g., ‘exercises’,
with the option of calling up the relevant ‘encyclopedia’ material at each
instant.
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Generally, we have used standard WWW and open-source software – i.e.,
software which is generally free and where the source code is freely
available and modifiable by the user – for implementing the modules. This
design philosophy has the advantage of making the application maximally
platform-independent, as well as providing a familiar interface – a standard
web browser – for students and faculty. Access to Internet for both students
and teachers is the only technical requirement for the collaborative learning
method proposed here.
3
Experience Using ITG at Uppsala University
Since the fall 2005 ITG is used as part of our courses Lingvistik I
(Linguistics I), Lingvistik II (Linguistics II) and Grammatik (Grammar) in
the Department of Linguistics and Philology, Uppsala University. We will
focus our attention here on Lingvistik I and Lingvistik II, where we have
primarily used only the Swedish corpora (POS-tagged and syntactically
annotated). The organization of these courses has been as follows: lectures,
group assignments and computer lab sessions. There have been three ITG
lab sessions in each course. The groups were divided into smaller sub-groups
consisting of 10–24 students in each sub-group. This was partly due to the
number of computers available in the computer lab and partly so that the lab
session leader could manage to supervise students individually. The students
had free access to ITG during the course period. During the first lab session,
the lab session leader (Mikaëla Lind) informed students about ITG, what a
corpus is and how it could be used for grammar training, and about the SUC
corpus. The focus in the first lab session has been on word formation, the
theme of the second session was parts of speech and the theme of the third
session was syntactic analysis.
Summaries of the student evaluations2 are presented below, classified
thematically (as some points occurred repeatedly in these evaluations).
3.1
Plenty of Group Opportunities
A recurring comment is that students would like more scheduled time
together with a teacher, and above all more group assignments. Thanks to
these lab sessions they get another three opportunities to practice and ask
questions in small groups. This is appreciated by the students. The
following are some comments from students (provided in English
translations):
I would like even more teacher guided group assignments.
2
Students fill in course evaluations anonymously in the middle of a course and at the
end of a course.
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The teaching was varied (lectures, lab sessions and group assignments).
The lab sessions are great fun and you learn a lot from them.
The lab sessions have been really good and instructive.
The lab sessions were great, everything became a lot clearer.
During the lab sessions in particular you get the opportunity to receive individual
help from the teacher, which has been very helpful and important.
The purposes of the ITG lab sessions varied depending on which course they
were part of, even if the instructions given to the students were the same. In
Lingvistik I they serve as an introduction and practice, in Grammar as an
exercise in order to strengthen knowledge. In Lingvistik II they are mainly
intended as repetition and are therefore placed at the beginning of the course.
This has been appreciated by those students who have not studied grammar
for a while as they, thanks to this warm up, then feel more prepared for the
more advanced level which is to come.
3.2 Good Mixture
A number of students commented that they like the fact that different kinds
of teaching methods are used – lectures, group assignments, and, ITG lab
sessions – as this combination provides a variation in teaching/learning.
Some are of the opinion that the lab sessions provide an opportunity for a
repetition, whereas for others it is an opportunity to learn and get some
clarity in linguistic analysis. In this way the ITG lab sessions allow each and
everyone to learn at their own pace and according to their own interests and
needs. These are two student comments:
The lab sessions are a useful supplement. If there is something you don’t
understand during a lecture you get another opportunity to listen, practice and
understand at a lab session.
The lab sessions are very helpful. They give an opportunity to, if you would like,
look at different items in depth.
3.3 Practising from Home
A lot of students consider it helpful to be able to practice from home with
the help of ITG. They get an introduction at a scheduled lab session and then
they practice as much as they like from home, thanks to having access to a
username and password valid throughout the course.
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3.4 Unnecessarily long
The first lab session felt unnecessary, one student comments. This is another
comment, possibly from the same person:
However, it has felt as if the lab sessions with ITG have been unnecessarily long
as you can just as well use the program from home and it gets a bit boring when
you have been using it for a while.
It would be sufficient to be given an introduction, and then you can go on
practising from home. However, our pedagogical idea is that the students
should be able to practise with a teacher present. We have noticed that
students, while working with ITG, raise questions about grammar and
language structure which would not have arisen if they were working with
traditional exercises. We believe that many of the students realized, for
instance that there is a difference between verb particles and prepositions,
and between predicatives and adverbials, thanks to plenty of practice. Many
times they need to put their questions at the start in order to understand the
following times.
3.5 Advantages of teaching in the computer lab
We have noticed that sitting in front of a computer has a number of
advantages for the students. Several people made notes by writing in a word
processor document instead of using pen and paper, which probably suits
some people better. In addition, some students (but surprisingly few) were
innovative and realized that they could look for information relevant for the
lab on the internet. For example when they were not sure about some part of
speech, they would look up a page on the net to read more, mainly on
Wikipedia and Nationalencyklopedin, we believe. Some thought of looking
for a definition of the word “lemma”, which is one of the tasks in the first
lab session. So, apart from being a useful tool for practising grammar, the
ITG lab sessions also give an enhanced possibility to search for information.
3.6 Co-operation
Working in a computer lab where students need to share computers, has the
advantage that students are encouraged to work together in teams, discussing
the problem and then arriving at a solution. One important duty of the
teacher in such situations is to encourage students to raise questions and also
to learn to discuss a theoretical issue. By verbalizing one's thoughts and
comments on how somebody else is thinking, one deepens and strengthens
the knowledge.
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4
Conclusion
To conclude, student evaluations suggest that students are mostly
appreciative of the ITG lab sessions as part of their regular course work. ITG
offers an accessible, flexible tool – based on natural language corpora – to
help them deepen their knowledge about grammar and do linguistic analysis.
Students find ITG flexible – it allows them to work at their own pace, and
also, if needed or desired, they use ITG anytime (and as much as they like)
during the course period from home or university any time of the day (apart
from the scheduled computer lab sessions). Further, it allows them to work
in small groups and with scope for discussions. In this way they learn by
doing linguistic analysis as well as discussing various aspects of grammar,
thus gaining a deeper understanding than would have been the case
otherwise.
References
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Lewandowska-Tomaszczyk and P.J. Melia (eds.), PALC 97: Practical
Applications in Language Corpora, pp. 51–62. ód University Press.
<http://www.sslmit.unibo.it/~guy/wudj1.htm>.
Ghadessy, M., et al. (eds.) (2001). Small Corpus Studies and ELT: Theory
and Practice. John Benjamins.
Johns, T. (1991). Should you be persuaded: Two examples of data-driven
learning. English Language Research Journal 4:1–16.
Knowles, G. (1990). The use of spoken and written corpora in the teaching
of language and linguistics. Literary and Linguistic Computing 5(1):45–
48.
Olsson, L.-J. and L. Borin (2000). A web-based tool for exploring translation
equivalents on word and sentence level in multilingual parallel corpora. In
Erikoiskielet ja kännösteoria – Fackspråk och översättningsteori – LSP
and Theory of Translation. 20th VAKKI Symposium, pp. 76–84.
University of Vaasa.
Saxena, A. and L. Borin (2002). Locating and reusing sundry NLP flotsam
in an e-learning application. In LREC 2002 Workshop Proceedings:
Customizing Knowledge in NLP Applications – Strategies, Issues and
Evaluation, pp. 45–51. Las Palmas.
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Prospects and Trends in Data-Driven
Machine Translation
Jörg Tiedemann
University of Groningen
Alfa Informatica
1
Introduction
In the past decade we have seen an amazing revival of machine translation
(MT) as the major field of research in computational linguistics. Many reasons
can be mentioned to explain this phenomenon: Globalization and the success
of the Internet may be one of them forcing companies and individuals to adapt
to a multilingual world. Political initiatives may also spur the fast development
of MT systems, especially for previously unsupported language pairs. The
increased capability of computers to handle large amounts of data might be
another factor contributing to the accelerated development especially of datadriven MT approaches. But we should not forget to mention that working with
translation is also a lot of fun attracting people all over the globe. And, finally,
MT is an appealing research area because it faces many unsolved problems
integrating various tasks in natural language processing.
In this paper we look at some general issues in data-driven machine translation and discuss possible strategies to improve translation quality. We review
some of the recent trends in the research community without looking into the
details of possible implementations and system development.
2
Typical Problems with Data-Driven MT
The current trend in MT research is to use existing large collections of data
to learn to translate from one language to another. This includes not only
parallel data from documents and their translations but also comparable corpora, monolingual corpora, bilingual dictionaries and other language(-pair)specific resources. The term data-driven techniques is very broad and does
not only include statistical and example-based approaches to MT. Rule-based
and dictionary-based approaches require real-world data almost as much as
their statistical counterparts. The difference between the various approaches
is the amount of trust the data is given, i.e., how much the translation model
159
is driven by the patterns found in the data and how much manual work is
needed to clean up and formalize them in the paradigm used. Especially the
last part, manual work, frightens many researchers and funding organizations
because of the risk of exploding costs and development time. This pushes them
towards fully automatic systems requiring more and more data and computational power for training. Progresss can certainly be seen with this approach,
however, translation quality is still poor when looking at the current state of the
art. Furthermore, data-driven MT bears the risk of turning MT into a research
competition with the focus on achieving the world record in BLEU scores. Instead one should concentrate on real users’ needs again: MT should provide
readable translations of texts not isolated sentences. It should not be based
on an optimized number of matching N-grams but should produce coherent
documents with some fluency across sentences.
2.1
Limited Use of Context
One of the main problems with current approaches to MT is the restriction
to the translation of isolated sentences. Most MT models consider the words
appearing in one sentence only without looking at any information from the
surrounding context. In this way the task of translation turns out to be very
hard even for trained human translators due to the large amount of ambiguities
in natural languages. On the other hand, human translators work differently,
taking a wide range of contextual clues into account when translating from
one language into another. Because of this, they have much less problems with
ambiguity than a computational model with limited context and no domain
knowledge. Most expressions can be translated unambiguously in their context even though they have several meanings in isolation or within the sentence
they appear in. A well-known principle in word-sense disambiguation (WSD)
is the “one sense per discourse” assumption (Gale et al., 1992) which is similarly applicable in machine translation. The possibilities and the usefulness
of WSD in machine translation has been discussed for a long time. In statistical machine translation (SMT), disambiguation is mostly left to the target
language model using local context only. Recently, WSD-style classifiers have
been integrated in SMT in order to improve phrase and word selection (Carpuat
and Wu, 2005; Giménez and Márquez, 2007; Vickrey et al., 2005). However,
they could only show modest improvements if any at all or limited themselves
to blank-filling tasks instead of full translation. The importance of wider context for disambiguation in SMT has already been recognized in Brown et al.
(1991). However, the integration of a WSD module with rich contextual features into a typical phrase-based MT system appeared to be unsuccessful until
some recent implementations (Carpuat and Wu, 2007a,b). According to their
findings it seems to be very important to develop a WSD module that is dedicated to the task of translation, i.e. focused on the proper selection of target
language words and phrases. Translation ambiguity is often different to the
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(1) Movie: Cheaper by the Dozen
Does this mean we can’t go to Dylan’s birthday party? - That’s exactly what it means.
- We bought his presents already.
- Vi har ju redan köpt hans present.
(2a) Movie: The Polar Express
He said Santa would have to fly faster than the speed of light ... to get to every house in one
night.
And to hold everyone’ s presents ... his sled would be bigger than an ocean
liner.
Och om alla julklappar skulle få plats måste släden vara större än ett fartyg.
(2b) Movie: The Polar Express
Checking out my presents .
Jag kollar också in mina julklappar .
Figure 1: Contextual clues for disambiguation.
one addressed in monolingual WSD. Furthermore, ambiguity is language-pair
dependent, i.e. polysemy may be (partially) preserved when translating from
one language to another or additional ambiguity can be introduced because of
a richer distinction between sub-senses in one of the languages. Hence, WSD
in MT has to be language-pair dependent and usually requires a rich set of
contextual and domain-specific features.
The importance of wider context for lexical choice can easily be seen in
some simple examples. Let us look at a corpus of translated subtitles (Tiedemann, 2007) which provides an interesting resource for translation issues across
various genres, domains and language pairs1 . For example, the English noun
presents can be translated into the Swedish counterparts presenter, gåvor or
julklappar. The first two are more or less synonymous whereas the latter is
used for Christmas presents only.
Looking at the examples in figure 1 we can see that none of the English
sentences to be translated contain a clear contextual clue to choose between
the general sense and the Christmas sense (besides the weak indication by sled
in 2a). However, the previous sentence in example (2a) contains the name
Santa which intuitively promotes the translation in the sense of Christmas
presents. Similar examples in which contextual clues can be found beyond
sentence boundaries are very frequent.
1
The subtitle corpus is a collection of 38,825 subtitle files in 29 languages. The
entire corpus is sentence aligned (361 language pairs) and covers 2,780 movies. It is
part of OPUS, which is a collection of parallel corpora and tools freely available at
http://www.let.rug.nl/tiedeman/OPUS/.
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The example (2b) in figure 1 shows another common case. Here, no contextual clue can be found even in the surrounding sentences (which are omitted
here). However, from before (example (2a) from the same movie), we know
that we talk about Christmas and, hence, the translation julklappar becomes
more plausible than presenter. This demonstrates how disambiguation decisions should be saved and considered in later cases.
There are many similar examples in our data collection. For instance, the
verb swings in a movie about Muhammed Ali is translated as slår (hits) whereas
it is translated as svänger in Der Untergang. For the latter we can find the contextual clue I want to dance in previous sentences. Similarly, fight is translated
as boxas throughout the Muhammed Ali movie whereas it is consistently translated as slåss in Gladiator and krigar in Helen of Troy. License is translated as
the general term tillstånd in The Godfather whereas it is translated as körkort
(drivers license) in the movie Taxi Driver (for which the title could be used as
a clue).
To sum up, it seems to be necessary to go beyond the sentence boundaries
when trying to resolve a large amount of ambiguities. Contextual clues should
also include information about domain and topic and in addition disambiguation should make use of previous decisions. The main difficulty is, of course,
the identification of appropriate patterns and the integration of disambiguation history. The risk is to give too much weight to spurious features in wide
context and to propagate errors.
2.2
Missing Quality in Generation
Naturally, most MT research is focused on the transfer of linguistic units from
source language to target language. On the other hand, the generation of proper
target language sentences is often simplified to a large degree. However, readability of a translation highly depends on the grammaticality and fluency of
the target language produced. It is not a coincidence that human translators
usually translate into their native language. Proficiency is needed much more
in the target language than in the source language. Despite of this fact many
MT systems spend more time analyzing the source language properly in order
to transfer all linguistic units recognized into appropriate target language expressions. Generation is then often a rudimentary component, for example, a
simple language model or a module fixing agreement and other morphological issues. Human translators on the other hand do not spend so much effort
in analyzing every single expression in the foreign language but focus on a
proper formulation in the target language. A fluent and grammatically correct
translation is more satisfying than a complete but unreadable translation even
if some minor facts are missing. Certainly, the translation should be as correct
as possible and should not change the meaning expressed.
The challenge for MT is to find a way to approach human translation with its
proficiency. An MT system should be able to grasp the general meaning of a
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foreign text (with permissible mistakes) and to generate perfect target language
output representing similar contents. For this, analysis and transfer could be
done on a shallow semantic level focusing more on the proper generation of
readable target language text. And, again, readability and fluency should not
be limited to isolated sentences.
Finally, generation should also take the type of reader into account. Proper
translation has to be adjusted to the actual user group which is targeted by the
translation. A text for domain professionals has different properties than, for
example, one produced for children or teenagers. Certainly, the original text
will be focused on a certain target group already but translation can still benefit
from modeling the target group of the translation appropriately.
2.3
The Trap of Open-Domain MT
Many MT projects emphasize the development of general-purpose open-domain
systems. However, working with a combination of various domains and topics leads to increased amounts of ambiguities that have to be handled. On the
other hand domain knowledge is important for proper translation and helps to
reduce ambiguity to a large degree. In many data-driven approaches the focus
is set on increasing the amount of training data to improve translation quality.
However, blending various domains into one general model also introduces
a lot of uncertainty into the system which is avoided if the domain could be
detected and designated models would be used to translate texts coming from
that domain.
As discussed earlier, ambiguous words are often translated consistently within
one text. Various senses can be ruled out when knowing the topic and domain.
Looking at human translators again we can see that they are topic aware and
often trained for certain domains. Hence, MT should not only be domain and
topic specific but should also use dynamic models that adjust themselves according to the contextual history. An open-domain MT system should then
work in the style of a mixture of experts in which translation is delegated to
the appropriate sub-domain model. And, the delegation should not only be
based on the current sentence but on recent context as well.
2.4
Oversimplification and Exaggeration
Even though many projects claim to work on hybrid systems we can still see
two major directions: rule-based MT systems with deep linguistic analysis
and statistical/example-based MT systems with shallow and often language
independent techniques. In hybrid approaches people try to integrate syntactic
information into statistical models and statistical information into rule-based
systems. However, the amount of linguistics and statistics used in these system
is usually fixed for any input. Purely statistical (language independent) approaches suffer from oversimplification in cases of complex linguistic patterns
163
which are difficult to transfer into similar target language units. Rule-based
systems suffer from exaggeration of linguistic processing in very simple cases
that would better be handled by simple pattern matching techniques. Furthermore, rule-based systems are not very robust in terms of handling unknown
constructions which leads to coverage problems.
Hybrid MT systems should tackle these problems in a clever way such that
each particular input is handled by only those components which can process
that type of data properly and most efficiently. Statistical systems should be
able to consult linguistic components in the cases where extra information is
needed (using some notion of uncertainty in translation for this translation).
Conversely, deep linguistic processing is not necessary in many cases, for example the ones that can be translated (almost) literally into the target language
(avoiding errors that may be introduced by the various components). Furthermore, it could be a good idea to leave elements underspecified if ambiguity
cannot be resolved with high confidence. Making no decision is often better
than taking the wrong turn. For example, the following translations (including
the metaphorical use of geschluckt (swallowed) in the sense of believing a lie)
can be found in the subtitles of the movie Good Bye Lenin:
Hat sie’s geschluckt?- Ja, klar.
Har hon svalt det ? - Ja , naturligvis .
Has she swallowed it ? - Yes , of course .
A deep semantic analysis of the source sentence would probably lead to a lot
of ambiguities possibly causing translation difficulties whereas the translation
is more or less literal in this example.
An MT system should choose the easiest way to get to the desired output
avoiding follow-up errors of non-perfect processing steps. The challenge is
to detect the amount of processing necessary for a particular input to allocate
appropriate units in the system and to estimate confidence in specific outputs
of various components.
2.5
Working with Sparse Data
Data-driven MT like all statistical NLP techniques is doomed to work with
sparse data. For example, sufficient data for statistical MT will always be
available only for a few language pairs and only for certain domains. Hence,
an important task in data-driven techniques is to make better use of the data at
hand. Comparing SMT/EBMT with human translators again, we can see that
there is an important difference in translation learning. In both cases examples of previous translations are used to improve translation skills. However,
statistical approaches to MT focus on handling larger amounts of data in order to improve coverage and quality, whereas humans are able to learn from
much fewer examples and even profit from looking at the same examples over
164
and over again. This is because humans analyze/generalize examples in many
different ways, looking for patterns and clues trying to understand these examples better and better. Machines could do the same, starting with simple
techniques, memorizing previous translations, finding frequent equivalents but
then starting to identify more complex, less frequent but important patterns in
the example data. Examples should be explored more exhaustively than done
by SMT and example-based approaches using broader context and more flexible patterns. Give the machine more time to learn instead of just more data!
There is more to discover in every text! Maybe machine learning techniques
should be developed which are closer to human learning considering the success of humans in tasks such as translation. This should probably also include a
component that filters extracted patterns in some post-processing step in order
to “forget” irrelevant information and to focus on quality instead of quantity.
3
What Can We Do?
Most of the issues mentioned above are difficult to address in automatic learning processes. Many research groups work on the integration of linguistic
knowledge and richer context into data-driven MT. The main issue is to find
a way to identify appropriate patterns in the data avoiding distracting signals
that lead to overfitting problems. The following discusses several ideas in addressing some of the issues mentioned in the previous sections without giving
a solution ready to be implemented.
3.1
Adaptive Models
Not without reason, domain adaptation is a hot topic in MT research. As discussed earlier a lot of ambiguity could be removed by considering information about domain and topic and by including broader contextual clues. Recent experiments in domain adaptation have shown that out-of-domain data is
very hard to handle by statistical (and probably other types of) MT systems
(Callison-Burch et al., 2007).
In SMT, a recent trend is to work with mixture models that include data from
various domains (Foster and Kuhn, 2007; Civera and Juan, 2007). Initially
people investigated adaptive language models in SMT using existing markup
or information retrieval techniques (Zhao et al., 2004; Byrne et al., 2004). The
target language model is responsible for a lot of disambiguation and, hence,
domain adaptation in this part of the system is a sensible thing to do. However,
lexical choice is of course also guided by the translation model and, therefore,
several groups have looked into the adaptation of translation models as well
(Hildebrand et al., 2005; Koehn and Schroeder, 2007). So far, the success is
rather modest but research in this field has just begun and will probably go
beyond the current results in the near future.
165
Future systems should include modules to detect domains and topics automatically. The output of this type of classification should be used directly by
the system to dynamically adjust parameters of the translation models. One
idea is to simply adjust the weights attached to components of a multi-domain
mixture model. Other ways of adjusting model parameters dynamically might
be possible.
Including contextual history into the system as discussed earlier could be
done by building cache-based translation models. In language modeling, caching
is known to reduce perplexity (Clarkson and Robinson, 1997; Iyer and Ostendorf, 1996) and similar techniques might be applicable in translation models as well. This would address the idea of consistently preferring certain
word/phrase senses within one text. Stylistic information might also be integrated into such a dynamic translation engine. Another idea is to allow the
system to benefit from user feedback in order to correct certain mistakes that
will lead to follow-up errors in the dynamic settings. Such negative data can
be very valuable for the success of the MT system in the future.
3.2
Proper Level of Complexity
Combining various approaches into one hybrid MT system is the goal for many
research groups. Defining a system with dynamic selection of strategies depending on the input is a challenging task. The main problem is to detect
the necessity of further processing. A simple approach could be to define a
cascading system with fallback strategies in which simple techniques are tried
first and in cases of low certainties more complex techniques are applied thereafter. Certainty can be measured using the internal parameters of the translation model or some kind of extrinsic evaluation of the output. For example
parsability could be a criterion or some measure of readability and fluency in
connection with previous context.
Another idea is to build a system that shows intermediate results to the user
but continuous processing with more complex models until the user stops the
process (or the entire process is done). In this way, the system would work as
an interactive system allowing the user to interrupt further processing. This enables the user to wait longer hoping for better results or to go further if satisfied
or in a hurry. Furthermore, post-correction could easily be integrated in such
an interactive system, again, helping the system to learn from the feedback by
the user.
3.3
Data Mining for Contextual Clues
In previous sections, we have discussed the necessity of rich contextual features to improve lexical choice and other types of disambiguation in MT. The
main problem is to identify appropriate patterns automatically in given training
166
data2 . The main problem here is the huge search space and the risk of including spurious features. It is not only that contextual features can be arbitrarily
far away but patterns may also include any combination of such features making it impossible to carry out an exhaustive search through the data. However,
certain strategies may help to explore the feature space systematically.
For word and phrase selection, we can first define default translations based
on the most frequent alignments found in the bilingual training data. The next
step is to search the example data for consistent indicators for each alternative
translation. This can be done by iteratively checking surrounding features,
starting with local context and then expanding to wider context and feature
combinations. Here, well-known data mining techniques for association rule
extraction can be applied.
Most of these algorithms are based on frequent set mining extracting rules
with high confidence and a minimum of support. The antecedent of such a
rule in our task would then be the contextual condition and the consequent
is the selected translation. For each ambiguous word or phrase a set of rules
could be extracted covering various kinds of contextual dependencies. Doing
this exhaustively for all words and phrases in the translation table is still not
feasible. However, it can be done for selected items to gradually improve
disambiguation in the system.
To test this technique on a tiny example we extracted the sentences and
their surrounding context (two sentences before and two after) that contain the
English word presents from our subtitle corpus and disambiguated each occurrence according to the alignment in Swedish. We kept only those sentences
for which the Swedish counterparts contain the strings presentera (to present),
present (a present), or julklapp (Christmas present). The term is actually not
very frequent in the corpus and after filtering there are 26 occurrences left.
Here, we limited ourselves to alphabetic surface words (in lower case) only
and ignored all other types of annotation we could use. Using an implementation by Borgelt (2003) of a standard algorithm for the extraction of association
rules, Apriori (Srikant et al., 1997) we obtained the following rules implying
the julklapp sense:
julklapp <- christmas (11.5, 100.0)
julklapp <- santa (11.5, 100.0)
julklapp <- santa and (11.5, 100.0)
Note that Santa never occurs within the same sentence as presents and also
Christmas is only in local context in half of the cases.
Due to the fact that we did not use any disambiguation based on part-ofspeech labelling the homographic use of presents as a verb can also be recognized by simple contextual rules. The following association rules (for sets
smaller than four words) have been found for the verb sense denoted by the
Swedish equivalent presentera:
2
Here, we consider the case of using parallel translation data to train the system.
167
presentera
presentera
presentera
presentera
presentera
presentera
presentera
presentera
presentera
presentera
presentera
presentera
presentera
presentera
presentera
presentera
presentera
presentera
presentera
presentera
presentera
presentera
<<<<<<<<<<<<<<<<<<<<<<-
ladies (11.5, 100.0)
gentlemen (11.5, 100.0)
ages (11.5, 100.0)
proudly (15.4/4, 100.0)
ladies gentlemen (11.5, 100.0)
ladies ages (11.5, 100.0)
ladies proudly (11.5, 100.0)
ladies all (11.5, 100.0)
ladies and (11.5, 100.0)
ladies the (11.5, 100.0)
gentlemen ages (11.5, 100.0)
gentlemen proudly (11.5, 100.0)
gentlemen all (11.5, 100.0)
gentlemen and (11.5, 100.0)
gentlemen the (11.5, 100.0)
ages proudly (11.5, 100.0)
ages all (11.5, 100.0)
ages and (11.5, 100.0)
ages the (11.5, 100.0)
proudly all (11.5, 100.0)
proudly and (11.5, 100.0)
proudly the (15.4, 100.0)
Here, proudly presents is a typical collocation in the corpus whereas the association to Ladies and Gentlemen usually involves wider context. Certainly,
the example above does not prove the usefulness of rule mining approaches in
MT. However, their potentials should be clearly visible.
There are many practical issues that have to be addressed in the rule mining approach. First of all, we still have to limit the context to be used even
in simple bag-of-words approaches. However, we can easily go beyond the
sentence boundaries as shown in the simple example above which is desirable
as we have discussed in earlier sections. Note that in real application we want
to include various kinds of linguistic annotation as possible features (part-ofspeech labels, chunk labels, dependency relations, etc). Another difference to
classical data mining techniques is that positional information might be important. Including positional dependencies would increase the search space
tremendously and, therefore, only some possibilities can be explored. Some
heuristics have to be defined to select specific settings to be checked by the
rule extraction algorithm. Again, one can start with simple features moving to
more complex ones.
A nice feature of a rule extraction approach is that intermediate results can
immediately be applied in the MT system. Training may continue infinitely
trying to explore other patterns in the example data using more and more complex feature sets. Furthermore, the exploration can be done in parallel for each
ambiguous item in the lexicon. A global search is not necessary.
A general problem with a data mining approach is the requirement of frequent sets. Interesting associations may be missed in this way due to sparseness of the data (a general problem in all data-driven techniques). There are
168
algorithms to extract high confident rules without minimum support. However,
there is a large risk of collecting noisy relations with spurious associations. It
might help to restrict the contextual freedom for such rules in order to decrease
the chance of such spurious rules. It could be an idea to define the minimum
support required for a rule as a function of feature complexity used in the antecedent of the rule.
Another idea is to merge contextual features of semantically related items
into semantic classes. For example, algorithms that explore distributional similarity in large monolingual corpora can be used to extract classes of related
words (Lonneke van der Plas, 2006). They can be used to form a contextual
feature representing the semantics of all these related words. The intuition
behind this is to obtain a higher level of abstraction and to focus on the meaning of words rather than their physical appearance in the text. In this way, one
hopes to find better generalizations with increased support and confidence. For
example, the translation of presents into the Swedish julklappar as discussed
previously may use the contextual clue of a word related to Christmas. The
problem, however, is the additional noise produced by the algorithms for extracting such classes and the ever increasing number of features.
The final task is to integrate the identified patterns into the MT system. This,
of course, highly depends on the general approach taken. A rule-based system
could simply create transfer-rules from contextual association rules found in
the data mining step. They might be validated by experts before being put to
use. Automatic validation using MT evaluation metrics may be another option.
In SMT systems association rules and the confidence scores connected to them
could be included as an additional component in the global statistical model.
Example-based MT systems could use them for ranking possible bitext pairs.
4
Conclusions
The main purpose of this paper is to collect ideas about possible improvements
of data-driven techniques in machine translation. The main claims can be summarized as follows:
• MT should go beyond translating isolated sentences. Wider context
should be used for disambiguation and for improving readability and
fluency of the output. For this contextual history should be cached and
used to adjust the MT model to the current discourse dynamically.
• The generation of the target language should be improved. Grammaticality and readability are neglected by many systems forgetting about
the real users needs.
• Domain knowledge and topic recognition should be integrated into widecoverage MT systems. The system should function as a mixture of translation experts with specific domain knowledge.
169
• Hybrid MT systems should take advantage of the success of different
approaches. However, the combination of various techniques should be
more flexible allowing the system to acquire additional information if
necessary but leaving things simple if possible.
• Data-driven techniques should make better use of the limited amount of
data available. Carefully mining example data for patterns may help MT
systems more than adding large amounts of noisy data.
• Mechanisms allowing the system to benefit from user feedback could
improve quality and validate model parameters.
Admittedly, none of the claims are carefully evaluated here and, therefore,
cannot be taken as the ultimate road for MT development. However, they are
meant to give inspiration to further advances in an exciting research area.
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172
Riding, Driving and Traveling – Swedish
Verbs Describing Motion in a Vehicle in
Crosslinguistic Perspective
Åke Viberg
Uppsala University
Department of Linguistics and Philology
1
Introduction
This paper will discuss a small but central group of motion verbs in Swedish
from a crosslinguistic perspective: the verbs describing motion in a vehicle.
Data will be drawn primarily from two translation corpora.
The lexicalization of motion verbs involves a variety of basic semantic
parameters which can take a number of values. Typologically Path (to/from,
up/down, in/out etc) has been the center of attention (Talmy 1985,
Bohnemeyer et al 2007) and this is indeed the most basic one, but there are
many other parameters that are relevant (see Viberg 1992, 2006a for an
overview of Swedish motion verbs).
An important characteristic of subjects that refer to human beings is their
propensity for self-propelled motion. This feature is acquired early by
infants (Spelke et al. 1995). Unlike a ball that starts moving because it is hit
by something, human beings have an inner source of energy, which can
make them move. Bodily locomotion verbs more or less by definition
describe self-propelled motion. But even motion by other types of subjects
such as natural forces (the wind, rain, etc) can be conceptualized as selfpropelled, which makes this a parameter that is not limited to bodily
locomotion. The most basic type of self-propelled motion for humans is
walking, which is expressed in Swedish with the verb gå described in an
earlier paper (Viberg 1999a). A smaller but rather central group of motion
verbs which typically take a human subject describe motion in a vehicle such
as ride and drive in English. Vehicle and means of transportation in general
represent a basic parameter that has traditionally been subsumed under
Manner. This paper will be concerned with the semantic differentiation
between the basic Swedish verbs rida, köra, åka, fara och resa as well as
with their patterns of polysemy which extend beyond the motion field.
Interestingly, the concepts of Force and Control are central as organizing
principles for most of them (the exception is resa) and for this reason
Swedish driva, the cognate of English drive, is also included in the
discussion. The paper will primarily be concerned with verbs that describe
motion in a vehicle in general and not with verbs that specifically refer to
173
aquamotion (Koptjevskaja-Tamm et al., forthc.) or motion in the air (flyga
‘fly’).
In this paper, Swedish will be compared to a selection of closely related
languages on the basis of data from two translation corpora. The analysis of
Swedish is also based on the monolingual corpora in the Swedish Language
Bank (Språkbanken). (Examples from these corpora have been translated by
me.) One of the translation corpora is the English Swedish Parallel Corpus
(ESPC) prepared by Altenberg & Aijmer (2000), which contains original
texts in English and Swedish together with their translations. The texts are
divided into two broad genres: Fiction and Non-fiction with several
subcategories. The original texts in each language contain around 500 000
words. The other corpus is more restricted and will be referred to as the
multilingual pilot corpus (MPC). It is being compiled by the author and
consists at present of extracts from 10 novels in Swedish with translations
into English, German, French and Finnish (totally around 250,000 words in
the Swedish originals). For some of the texts, there are also translations into
Danish and Dutch. As an illustration of the types of data this article is based
on, examples from the corpus are shown in table 1. I will use some of the
examples to introduce the major semantic parameters that will be treated in
this paper.
One basic contrast is the differentiation between verbs profiling the control
of a means of transport, such as riding and driving, versus the profiling of
being transported, such as traveling and voyaging. The verb rida ‘ride’ is not
as frequent as the other verbs but has been included since verbs with an
equivalent meaning have extended their meaning in some of the other
languages. This is most striking in Dutch, where rijden still can be used
about riding a horse but is also frequently used with reference to driving and
traveling in a car (and other vehicles). The basic Swedish verb used to
express the driving of a car or other vehicle is köra ‘drive’ and this contrasts
with åka and fara which profile the sense of being transported. Usually, the
meanings do not mutually exclude one another: driving strongly invites the
inference that the driver is being transported but not necessarily since you
can drive certain vehicles with a remote control (in particular model cars).
The verbs åka and fara can be used even when the subject refers to the
driver but the control of the vehicle in this case is backgrounded. These
verbs cannot be used when the control is strongly profiled as in “Do you
know how to drive?” This contrast is not upheld lexically in several
languages.
German tends to use the verb fahren, the cognate of Swedish fara, both to
express driving and traveling, whereas Danish tends to use køre, the cognate
of köra ‘drive’ with both of these meanings. Finnish ajaa has both of these
uses, too. Compare examples (2) and (4) in table 1. A further semantic
contrast is shown in example (5). Swedish köra can be used as a verb of
transportation in a vehicle, where the displacement of the object of the verb
is profiled. Danish køre and Dutch rijden can cover this sense as well.
174
(1)
Swedish:
English:
German:
French:
Finnish:
Danish:
Dutch:
”Rida skulle vi”, sa Ronja. AL
“We were going to ride,” said Ronia.
„Reiten wollten wir”, sagte Ronja.
„Tout ce qu’on voulait, c’était monter à cheval”, dit Ronya.
– Meidän piti kai ratsastaa, Ronja sanoi.
”Vi skulle jo ride,” sagde Ronja.
„We zouden toch gaan rijden,” zei Ronja.
(2)
Swedish
English
German
French
Finnish
Danish
Dutch
Och frun kunde inte köra traktorn. KE
and his wife couldn't drive the tractor.
Und seine Frau konnte nicht Traktor fahren.
Et sa femme ne savait pas conduire le tracteur.
Eikä vaimo osannut ajaa traktoria.
Og konen kunne ikke køre traktoren.
en zijn vrouw kon geen tractor rijden.
(3)
Swedish
English
German
French
Finnish
Danish
Dutch
Åk med ner. KE
Come on down with us.
Fahr mit runter.
Va avec eux.
Lähde mukaan
Kør med ned
Rijd maar mee.
(4)
Swedish
English
German
French
Finnish
Danish
Dutch
och de for tillbaka till campingen. KE
so they went back to the camping site.
und die beiden Männer fuhren zum Campingplatz zurück.
et ils retournèrent au camping.
ja he ajoivat takaisin leirintäalueelle.
og de kørte tilbage til campingpladsen.
en ze reden terug naar de camping.
(5)
Swedish
English
German
French
Finnish
Danish
Dutch
Annie behövde inte köra henne sa hon. KE
Annie needn't drive her down, she said.
Annie brauche sie nicht zu fahren, sagte sie.
Ce n'était pas la peine qu'Annie la conduise, dit-elle.
Hän sanoi ettei Annien tarvinnut lähteä viemään.
Annie behøvede ikke at køre hende, sagde hun.
Annie hoefde haar niet te rijden, zei ze.
Table 1: Verbs describing riding and motion in a vehicle in the MPC corpus.
Verbs of traveling contrast with verbs describing self-propelled motion,
the basic form of which is walking (for human beings). Languages differ
with respect to whether there is a (more or less) obligatory contrast between
walking and being transported in a vehicle. In Swedish, the verb gå ‘go’ can
only be used with reference to walking (when the subject is human), and this
leads to a frequent error even among many rather advanced learners of
Swedish as a second language who can say Jag gick med tåget/bilen till
175
Uppsala ‘I went by car/train to Uppsala, where åka must be used. One
source of contrastive data for Swedish verbs of traveling is the Swedish
grammar intended for Swedish as a second language, which has been
translated into 18 languages (Viberg et al. 1984–). Examples (6)-(7) are
taken from various versions of the grammar (op. cit. §15.5).
(6)
Swedish:
English:
Greek:
Rumanian:
Turkish:
Min fru måste åka tunnelbana till jobbet.
My wife has to go to work by underground.
I jinéka mu prépi na pái me ton elektrikó sti uliá.
Soia mea trebuie s mearg cu metroul la service.
Karım iine tunnel ile gitmek zorundadı
(7)
Swedish:
English:
Greek:
Men min arbetsplats ligger så nära att jag kan gå.
But my office is so close that I can walk.
Enó i ikí mu uliá íne tóso kondá pu boró na páo me ta
póia.
Locul meu de munc este îns aa de aproape, încît pot s
merg pe jos.
Ama benim iyerim çok yakındır, ben iime yürüyerek
gidibilirim.
Rumanian:
Turkish:
Data from a pedagogical grammar are not as reliable as data from corpora
but the general picture appears to be correct. The verbs used to express the
meanings of Swedish gå and åka and the other Swedish verbs discussed so
far are shown in table 2. As can be observed, the verb corresponding to ‘go’
is also used to describe motion in a vehicle in English, (Modern) Greek,
Rumanian and Turkish. In Greek, it is also used to express transportation in
a vehicle. Thus, there is no obligatory contrast corresponding to that between
gå and åka, even if specific verbs describing motion in a vehicle exist and
are used to various degrees. (The Swedish verb resa is translated with such a
verb except in Turkish.) In addition, all four languages have a separate verb
that can be used when the subject refers to the driver operating the vehicle.
In general, it can be concluded that verbs describing motion in a vehicle
have many language-specific (but not necessarily unique) features in
Swedish. In the following, these verbs will be looked at one by one in
greater detail.
176
Swedish:
English:
Greek:
Rumanian:
Turkish:
Self-propelled motion on foot
gå
go/walk
páo
a merge
gitmek/yürümek
Swedish:
English:
Greek:
Rumanian:
Turkish:
Motion in vehicle – being transported
åka/fara, resa
go, travel
páo, taksiévo
a merge, a cltori
Gitmek
Swedish:
English:
Greek:
Rumanian:
Turkish:
Motion in vehicle – operate vehicle
köra
drive
oió
a conduce
sürmek
Swedish:
English:
Greek:
Rumanian:
Turkish:
Transportation in vehicle
köra
drive
páo
a conduce
sürmek/götürmek
Table 2. The basic verbs for expressing self-propropelled motion and motion
in a vehicle in Swedish and four other languages (based on Viberg et al
1984-, §15.5)
2
From Horse to Automobile: The Verb ‘Ride’
The verb ride is a common Germanic verb with cognates in all the major
Germanic languages. In Swedish, the verb has the form rida. The meaning
‘move sitting on top a horse and controlling its movement’ is still the
dominant meaning in Swedish, where rida has not been extended to cover
motion in a vehicle such as a car or a bicycle. These meanings are primarily
covered by åka, whose meaning to a great extent overlaps with the presentday extended use of ride and its cognates, in particular in Dutch, as we have
seen, but also to a certain extent in English. Since there are many interesting
parallels to Swedish åka, a sketch of the meaning patterns of English ride is
given in figure 1. This figure, like all the following figures of the same type,
primarily shows sense relations in present-day English (or Swedish in
sections below). Diachronic relationships are reflected only to the extent that
177
they are stated explicitly in the text. (Unlike the following figures, this one is
not based on any systematic corpus study.)
Peter rode home
(on his bike).
Prototype
Peter rode home (on his horse).
(i) sit on top
(ii) control
(iii) travel
(i) sit on top of horse
(ii) control horse
(iii) travel
Focus:
On top
The ship is
riding on
the waves.
Focus:
Control
The politican was
riding on popular
discontent.
Focus:
Travel in
a vehicle
Drawn by a horse
(hist.)
The king rode to
the cathedral in an
open carriage.
Your boss is
riding you much
too hard.
Any vehicle
Peter rode to
New York (in
a car/ bus/
train…)
He rode
in an
elevator.
For vehicle
to travel
in a certain
manner
This car rides
smoothly.
Subject: Item of
clothing
His T-shirt rode
up.
Figure 1: The meaning patterns of English ride (somewhat sketchy).
The common Germanic prototype of ‘ride’ seems to combine three major
components (i) sitting on top a horse (ii) controlling the movement of the
animal (iii) displacing oneself in this manner. Various secondary meanings
focus parts of the prototypical meaning. With a vessel as subject, the notion
178
‘on top of (the waves)’ is focused, and in this case rida can be used in
Swedish as in (7).
(7)
the boat riding a run of wave prow up. DT
eftersom båten red på en våg med stäven i vädret,
Another case, where sitting on top is rather prominent is ride on a bike, but
in this case rida cannot be used in Swedish but only cykla ‘cycle’ or åka
cykel (see 8).
(8)
Her upper lip was puffy, like the kind of scrape children get falling off
bicycles when they first learn to ride. SG
Hennes överläpp var svullen.Det liknade den sorts blessyr små barn
brukar få då de ramlar omkull när de lär sig cykla.
The notion of control, which is closely related to ‘on top’ (CONTROL IS
UP), is focused in a number of metaphorical uses such as The politician tried
to ride on popular discontent, which has a close Swedish equivalent. There
is also a verb such as topprida ‘ride on top’, which is used metaphorically
(Så länge valuta- och räntemarknaderna topprider den svenska demokratin
P95). The most important set of extensions focuses on the fact of traveling,
keeping the manner component in the background. Already in Middle
English, ride could take on the extended meaning ‘to be conveyed in a
wheeled or other vehicle drawn by a horse’ (OED). From this, there was a
short step to riding in a train or a car, once these means of conveyance had
been invented. With this extension, the meaning of ride is approaching the
central meaning of the Swedish verb åka, non-self-propelled motion. In
most cases where ride is used with reference to traveling in a conveyance,
åka is used in Swedish as illustrated in (9) and (10).
(9)
(10)
The dogs ride, the poor walk, or go by bus. FW
Hundarna åker bil; de fattiga går eller åker buss.
He refused to speak or even look Andrew in the eye as they rode to the
fourth floor. AH
Han vägrade säga något eller ens möta Andrews blick när de åkte upp
till fjärde våningen.
The use in (11), which is restricted to items of clothing according to
Cambridge International Dictionary of English(CIDE), also has a parallel in
the use of Swedish åka (my translation):
(11)
His T-shirt rode up, when he bent over. CIDE
Hans T-shirt åkte upp, när han böjde sig framåt.
If the interpretation sketched here is correct, there are two prototypical
clusters in the meaning pattern of English ride. One is centered on the
original prototype ‘ride on a horse’, and the other is emerging around the
meaning in present-day English ‘ride in a conveyance’. This latter meaning
179
has no counterpart in Swedish, but as we have seen rijden ‘ride’ has
extended even further in Dutch.
3
Driving
According to Buck (1949), many of the words for ‘drive’ in Indo-European
languages were originally used in the context of driving cattle (in front of
oneself, as opposed to ‘lead’). Another source is words with the opposite
meaning, ‘lead’, which according to Buck applies to Romance words for
driving such as Rumanian conduce, French conduire, Spanish conducir. The
human agent in this situation acts as an outside force causing the cattle to
move. Thus not only the idea of riding in a car as a passenger, but also the
notion of controlling and driving a car were originally modeled on the
guidance of domesticated animals. Other words for ‘drive’ have developed
from ‘strike’ or ‘push’, both of which are centered on Force (see Viberg
1999b for striking). As will be demonstrated in this section, Force or
Power/Control is also central in the meaning of verbs used about driving a
car or other vehicle in modern Swedish and English.
3.1 The Swedish Verb Köra: ‘Drive (a Vehicle)’
When the operation of a vehicle (typically a car) is profiled köra is used in
Swedish. The profiling is particularly clear when a vehicle appears as direct
object as in (12).
(12)
Swedish:
English:
German:
French:
Finnish:
Ska du köra ambulans om du inte är nykter? PCJ
”Do you drive an ambulance even when you're not sober?”
„Willst du denn den Krankenwagen fahren, wenn du nicht
nüchtern bist?“
–Tu vas conduire ton ambulance même après avoir bu ?
–Voitko ajaa ambulanssia, vaikka et ole selvä?
English and French in this case have special verbs (drive, conduire), whereas
German and Finnish has one and the same verb corresponding to köra
‘drive’ and åka ‘ride in a car etc.’. The contrast can be signaled by using
different constructions. To profile ‘driving’, the vehicle appears as direct
object as in (12) marked with the accusative in German and with the
partitive in Finnish (alternating with the accusative in other examples).
When the operation of the vehicle is not profiled as in (13), åka can be used
even when the subject actually refers to the driver. In German and Finnish,
the vehicle is marked as an instrumental (prep. mit ‘with’ in German and
adessive case –lla(-llä) in Finnish.) If the subject of the verb refers to the
driver of the vehicle, the choice between köra and åka is a question of
profiling, since the driver simultaneously is being transported in the vehicle
(in most cases).
180
(13)
Swedish:
English:
German:
French:
Finnish:
Hon hade åkt bil här massor av gånger LM
She had driven past here many times
Unzählige Male war sie hier mit dem Auto entlanggefahren
Elle était passée par là en voiture à maintes reprises,
Hän oli ajanut täällä lukemattomia kertoja autolla
As illustrated earlier in (5), köra can also be used as a verb of transport
describing the movement of the object by driving a car or other vehicle. In
this case, köra alternates with skjutsa which usually refers to human
passengers and frakta which tends to refer to goods of various types.
Examples (14) and (15) are from the ESPC. There are several further types
of transportation verbs in Swedish referring to specific types of cargo or
vehicles (see Viberg 1981, 59-62).
(14)
(15)
Gammlundström brukade skjutsa henne, TL
Old Lundström used to drive her there,
De stora spanska skeppen fraktade handelsgods från Amerika, BTC
Great Spanish ships carried freight from trade with America
The uses of köra involving a vehicle are the most frequent ones in presentday Swedish. The verb can, however, be used with reference to other types
of forced motion. As is indicated in figure 2, the notion of causing
something to move with force is the general (schematic) meaning of köra,
which is shared by most uses. One set of uses describes how something held
in the hand is set into motion, usually in a forceful way.
(16)
Swedish:
English:
German:
French:
Finnish:
Björne körde en knytnäve i magen på honom. KE
Björne drove his fist into his stomach,
Björne jagte ihm die Faust in den Bauch.
Björne lui enfonca un poing dans le ventre.
Björne iski häntä nyrkillä vatsaan.
The verb köra can also be used to describe how people or animals are driven
away, usually verbally with a sharp order or (in the case of cats and similar
animals) with a specialized interjection such as shoo! (Swedish schas!,
which can be derived as a verb schasa ‘shoo’ vb.). (17) and (18) are taken
from the ESPC.
(17)
(18)
Bara öronen viftar till då och då som för att köra bort en fluga. PCJ
Only his ears move now and then, as if shooing away a fly.
De kom alltid omgående och körde bort de som störde honom. HM
They always came right away and drove off anyone who was
disturbing him.
The dominant meaning of köra in present-day Swedish is related to
operating and traveling in a vehicle. However, the verb has a number of
other uses that share a schematic meaning which can be expressed
181
approximately as “Forcefully cause to move”. In a way, the meanings related
to operating a vehicle are set off from the rest of the meanings.
FORCEFULLY CAUSE
TO MOVE
Operate a vehicle
Per kan köra bil.
Per can drive a car.
Cause a bodypart to
move
Per körde ner händerna
i fickan.
Per put his hands in his
pockets.
Cause humans
or animals to
move away
Per körde bort
alla nyfikna.
Per drove away
all the curious
people.
Per körde ut
katten.
Per chased the
cat out.
Cause a physical object
to move holding it in
the hand
Soldaten körde ett
svärd genom tältduken.
The soldier pushed a
sword through the side
of the tent.
MOVE IN A
VEHICLE while
operating it
Per körde hem.
Per drove home.
TRANSPORT IN A
VEHICLE
Per körde Eva till
flygplatsen.
Per drove Eva to the
airport.
For VEHICLE to
MOVE
Bussen körde iväg.
The bus drove away.
Figure 2: Meaning patterns of the verb köra.
3.2 The Cognates English Drive and Swedish Driva
As shown above, drive is the most frequent English translation of köra,
which in its turn is the most frequent translation of drive in the ESPC.
However, the relationship is not completely symmetrical. Even if köra is the
most frequent equivalent of drive, there is a second equivalent that is
relatively prominent, namely the Swedish cognate driva. In the ESPC, köra
182
accounts for 102 (53%) and driva for 35 (18%) of the equivalents of the 192
occurrences of drive in the English texts. Swedish driva expresses the
application of force in various ways. The following example with a human
object is parallel to example (18) with köra:
Subject-centered motion
Human
MOVE AROUND
AIMLESSLY
Physical object
MOVE DRIVEN
BY EXTERNAL
FORCE
Båten/Dimman drev
mot land. The
boat/mist drifted
towards the shore.
Anna drev omkring i
Gamla stan. Anna
drifted around in the
old town.
Object-centered motion: CAUSE TO MOVE IN FRONT
Human
Natural force
Emotion/Mental
Herden drev in fåren i
fållan.
The shepherd drove
the sheep into the fold.
Control the
activities in a
business
Hon drev en
resebyrå.
She ran a travel
agency.
Vinden/Vågorna drev
båten i land.
The wind/waves
drove the boat
ashore.
Cause to be
moved in a
ridiculous
direction
Alla drev med
honom.
Everybody made
fun of him.
Hungern/Hans
nyfikenhet drev
honom att återvända.
Hunger/His curiosity
drove him to return.
Cause someone to
Cause a mental
move into a
object to move
through a psycho- psychological state
logical barrier
Hon drev sin syster
Vi lyckades driva till nervigenom våra krav. sammanbrott.
She drove her
We succeeded in
sister to a nervous
pushing through
breakdown.
our demands.
Figure 3: The polysemy of Swedish driva.
(19)
Swedish:
English:
German:
French:
Finnish:
Utan förskoning drev hon ut dem i snön, KE
She drove them out into the snow without mercy,
Ohne Erbarmen trieb sie alle hinaus in den Schnee
Sans se laisser apitoyer, elle les fit sortir dans la neige
Loviisa ajoi ilman armoa ryövärit hankeen,
183
Swedish driva can be used with both human and more abstract subjects as
demonstrated in figure 3, which accounts for the major meanings of driva. A
relatively common subject of driva is a Natural force such as Wind or
Waves, which typically can drive a ship or other Natural phenomena such as
clouds and mist. In Novels 81, examples are found such as (somewhat
shortened): Vinden drev båten långsamt framåt ‘The wind drove the boat
slowly forwards’ and Vinden drev dammet längs gatorna ‘The wind drove
the dust along the streets’. Related to this use is (20) from a popular science
text (ESPC):
(20)
Denna självreglerande process sker aktivt och drivs av den fria energi
som kommer via solljuset.
The self-regulation of the system is an active process driven by the
free energy available from sunlight. JL
Both English drive and its Swedish cognate can also be used about
psychological forces causing mental processes as in (21).
(21)
Vad jag tror är att Byrons inre främling var lynnigare än min och att
den drev honom till större överdrifter och större ånger. SCO
What I think is that Byron's inner stranger was more capricious than
mine, and drove him to greater exaggerations and greater regrets.
With a human subject, driva can be used with both concrete and abstract
objects, for example a business or enterprise as in (22)
(22)
Tillsammans med min hustru Louise driver jag Åkerbloms
Fastighetsförmedling. HM2
I run Åkerblom's Real Estate with my wife.
Swedish driva can also be used intransitively with the moving Theme as
subject as in (23) and (24). In this use, driva describes non-self propelled
motion or motion without a clear aim. The most direct equivalent appears to
be drift in English. Similar to many of the motion-in-vehicle verbs, driva
alternates its meaning from exerting force (in its transitive uses) to lack of
control (in its intransitive uses).
(23)
(24)
184
Jag hade drömt att Rustica drev redlös med tidvattnet mot Stromas
klippor. BL
I had dreamt that Rustica, disabled, was drifting with the tide towards
the cliffs of Stroma.
Zigenarna, som de kallar ’los egipcianos’, är förbjudna att i
fortsättningen driva omkring i riket. BTC
The gypsies, whom they call “los egipcianos”, will in the future be
forbidden to wander about in the kingdom.
It has only been possible to exemplify a few of the many different uses of
driva. Figure 3 does not provide a complete account either but should suffice
to show that the various meanings are interrelated in a systematic (but not
completely predictable) way.
4
The Swedish Verbs of Travelling: Åka, Fara, Resa
As noted above, the Swedish verb gå cannot be used with a human subject
when a vehicle is involved, since gå implies that the motion takes place on
foot. There are basically three alternatives apart from verbs that incorporate
a specific vehicle, namely the verbs åka, fara and resa which will be
considered in this section. The major translations of these verbs in the
Multilingual Pilot Corpus (MPC) are shown in table 3, which will be
commented on below.
4.1 The Verb Åka and Non-Self-Propelled Motion
According to Buck (1949), Swedish åka is a late reflex of an Indo-European
root *a- with the primary meaning ‘drive’, which is reflected in Greek ‘lead’ and Latin agere ‘drive, carry on, act, do’. In Medieval Swedish, the
verb aka covered both driving and traveling (Söderwall gives two senses: 1)
köra, föra på vagn eller i släde; 2) åka). In present-day Swedish the verb is
restricted to traveling. Thus, there is a development from ‘driving’ to
‘traveling’.
Today, åka is the dominant expression for ‘traveling in a vehicle’ in
Swedish. The MPC languages all have a verb with a corresponding meaning
but the degree to which such a verb is used varies a great deal, as can be
observed in table 3. In English, the most frequent translation is the nuclear
motion verb go, whereas the most frequent verb indicating the means of
transportation is drive, which more directly corresponds to köra.
The English verb that most directly expresses the meaning that the subject
is being transported by some means of transportation is ride as in examples
(9) and (10) in section 2. One characteristic of åka is that it can be used as a
verb of departure as in (25).
(25)
Swedish:
English:
German:
French:
Finnish:
Gudrun hade satt fram kaffebröd innan hon åkte. KE
Gudrun had put out bunloaf before she had left.
Gudrun hatte Kaffeegebäck hingestellt, bevor sie gefahren war.
Gudrun avait sorti des petits gâteaux avant de partir.
Gudrun oli pannut pöydälle kahvileipää ennen kuin lähti.
In (25), hon åkte ‘she traveled’, which does not have any explicit
specification of Place, implicitly indicates ‘from here’ (i.e. the focus place)
similar to expressions like she left (or she went). The other languages (except
German) in this case use a verb of departure. As can be observed in table 3,
this tendency is most pronounced in Finnish, where lähteä ‘leave’ is actually
185
The prototypical meaning: TRAVEL IN A VEHICLE
TranslaType of motion verb used as translation
tion into
Nuclear
Departure
Directional
’go’/’come’
’leave’
åka N
English
go
come
31
4
German
gehen
komme
n
2
1
French
Finnish
aller
venir
mennä
tulla
9
5
9
2
leave
partir
s’en
aller
lähteä
10
15
4
return
Means of
transportation
73
1
rentrer
retourner
6
3
descendre
passer
3
3
32
drive
travel
11
2
fahren
fliegen
57
1
reisen
1
conduire
voyager
1
1
ajaa
matkustaa
15
7
33
fara N
English
go
11
leave
3
cross
2
German
French
Finnish
mennä
1
drive
travel
11
3
fahren
reisen
27
1
partir
5
Various
8
voyager
1
lähteä
6
ylittää
1
ajaa
matkustaa
12
4
18
resa N
English
go
6
leave
2
German
French
Finnish
venir
1
partir
s’en
aller
8
2
lähteä
1
parcourir
1
travel
drive
7
1
reisen
fahren
fliegen
10
4
1
voyager
3
matkustaa
9
Table 3: Major translations of the Swedish verbs åka, fara and resa in the
Multilingual Pilot Corpus (MPC) used as verbs of traveling.
186
the most frequent translation of åka. Particularly in French, there is a
tendency to use a directional verb unmarked for any type of manner such as
descendre ‘move down’ and passer ‘pass’. In spite of the fact that there exist
verbs indicating means of transportation in all the MPC languages, there are
remarkable differences with respect to the frequency with which they are
used as translations of åka. French only in two cases uses such a verb.
German, on the other hand, with very few exceptions uses fahren as a
translation of åka. Finnish uses ajaa ‘drive, travel’ to a certain extent but the
verb of departure lähteä ‘leave’ is actually the most frequent translation. In
English, the most frequent translation is the nuclear verb go. The nuclear
verb meaning ‘go’ is used relatively frequently as a translation also in
French and Finnish but not to the same extent. As shown in Viberg (2006a),
the use of åka with reference to motion in a vehicle is clearly dominant in
Swedish, accounting for close to 90% of the occurrences in novels, for
example. Still, åka has an interesting pattern of polysemy which is shown in
figure 4. All the uses of åka share the schematic meaning non-self-propelled
motion. This is true even when the subject is non-human as in (26). A verb
in the passive or (in French) reflexive form appears as a translation.
(26)
Swedish:
English:
German:
French:
Finnish:
fönstren åker upp, MA
the windows are flung open
die Fenster werden aufgerissen
les fenêtres s'ouvrent,
ikkuna avataan
Many of the uses of åka imply a lack of control on the part of the subject,
which is closely related to the notion non-self-propelled motion. This is
evident when the subject refers to a body part as in (27).
(27)
Swedish:
English:
German:
French:
Finnish:
Ibland gapade han lätt och ögonlocken åkte ner. KE
his mouth occasionally dropping open and his eyelids
drooping.
Manchmal gähnte er flüchtig, und die Augendeckel fielen
ihm zu.
Par moments, il bâillait un peu et ses paupières se fermaient.
Häntä haukotutti ja hänen silmä-luomensa lurpahtelivat
The notion of lack of control is even more prominent in a set of partly
idiomatic phrases sharing the meaning ‘End up in an unpleasant situation’
such as åka dit ‘be caught (by the police)’ shown in (28).
(28)
Swedish:
English:
German:
French:
Finnish:
Vi skulle åka dit direkt. MA
We'd be locked right up.
Wir sollten direkt hinfahren.
On serait coincées illico.
Me jäisimme heti kiinni.
187
There does not seem to be any general equivalent to åka used in this sense.
These uses of åka are very colorful and it seems that translators, correctly,
concentrate on rendering the correct associations of such expressive uses of
words. (See Viberg 2006a for more examples of English translations in
ESPC) .
Non-prototypical vehicle
Kalle åkte cykel / skidor...
Charlie was riding a bike/ skiing....
Dominant
meaning
TRAVEL IN VEHICLE
Kalle åkte buss till jobbet.
Charlie went by bus to his job.
Schematic meaning:
Non-Self-Propelled Motion
Subject :Human
Kalle åkte av
gungan.
Charlie slipped
off the swing.
Bodypart
Handen åkte upp
till munnen.
His hand rose to
his mouth
Vehicle
Bussen åkte iväg.
Physical object
Tröjan åkte upp.
The bus left.
The sweater
glided up.
Specialization:
Ending up in an unpleasant situation
Kalle åkte ut.
Charlie got
thrown out.
Kalle åkte fast.
Charlie got
caught.
Kalle åkte dit.
Charlie got
nailed.
Kalle åkte på en
snyting.
Charlie got himself
punched on the nose.
Figure 4: The meaning pattern of åka.
The schematic meaning non-self-propelled motion is shared by practically
all uses of åka. The exceptions are expressions such as åka skidor ‘ski’ and
åka skridskor ‘skate’, where the means of transportation require bodily
188
activity. However, the sense of lack of control is totally absent when åka
refers to motion in a vehicle. In the majority of cases, traveling in a vehicle
is an intentional act. In this respect, the more specialized uses represent a
further step away from the historically more active basic meaning (‘drive’
etc.)
4.2 The Verb Fara and Rapid, Violent Motion
The Swedish verb fara is a verb with cognates in most of the modern
Germanic languages, which originally had a very general meaning as a
motion verb. The verb fara is still the most frequent motion verb in modern
Icelandic (Pind 1991) and the same applies to one the most conservative
Swedish dialects Elfdalian (Älvdalska), where fårå ‘go, travel, move’ is the
most frequent motion verb, slightly more frequent than kumå ‘come’
(Steensland 1986). In modern standard Swedish, it can be used as an
alternative to åka but is less frequent in this use and is perceived as
somewhat formal and/or old-fashioned by many speakers, although there is
variation on this point since the verb appears to be in more general use in
certain regional varieties of Swedish. The following account is based on
printed texts. In its use as a motion-in-vehicle verb as in (29) it has a
translation pattern that is similar to that of åka as can be observed in table 3,
which accounts only for this use of fara.
(29)
Swedish:
English:
German:
French:
Finnish:
Wallander for hem. HM
Wallander drove home.
Wallander fuhr nach Hause.
Puis il reprit sa voiture et rentra chez lui,
Wallander ajoi kotiin.
In addition to this use, fara has a number of other uses which form a rather
complex pattern of polysemy shown in figure 5. Several of these specialized
meanings are realized as phraseological units of various types with
idiosyncratic semantic and/or formal properties which are more or less
lexicalized and will not be described in detail but they all share the
schematic meaning ‘travel fast and/or violently and without (full) control’.
With a human subject, the motion may be self-propelled as in (30) and (31),
but lack (or low degree) of control is usually prominent.
(30)
Swedish:
English:
German:
French:
Finnish:
Jävlar! Han for upp ur stolen, PCJ
Heck! He leaped out of the chair –
Verdammt! Er sprang auf,
Merde! Il sauta hors de la chaise.
Hitto! Hän hyppäsi tuolista,
(31)
Swedish:
English:
German:
Runt i förrådet for han och hotade, MN
He charged round and round the shed, growling out threats:
Er lief im Schuppen herum und stieß wilde Drohungen aus,
189
French:
Finnish:
Il parcourait la réserve en proférant des menaces,
Hän kolusi varaston laidasta laitaan ja uhosi,
With a bodypart as subject, the use of fara describes an uncontrolled and
rapid movement of the limb:
(32)
”Ärrnäsan” ryckte till som om han ertappats med något olagligt och
högerhanden for in under slängkappan i en van gest. ARP
Fastighetsförmedling. HM2
‘Scarnose’ jumped as if he had been caught out doing something
illegal and, out of habit, his right hand dived in under the cloak.
A variety of non-concrete subjects are also allowed. However, the
progression from concrete subjects that can be perceived by the external
senses to more abstract subjects is continuous and does not justify the
postulation of metaphorical shifts between incompatible domains. Certain
emotive, physiological reactions can be clearly localized spatially as in (33).
(33)
En rysning for längs ryggraden.
A shudder ran down his backbone.
Subjects belonging to the semantic class Verbal communication such as
‘word’, direct quotes etc can be conceived of both as mental objects and as
sounds which at least have sources (and partly also targets or receivers) that
can be located in physical space. All the MPC languages use motion verbs as
translations of fara (34) but the basic meaning varies a great deal.
(34)
Swedish:
English:
German:
French:
Finnish:
Svordomarna for ur mun på henne, MF
oaths pouring out of her mouth,
Sie stieß Flüche aus,
Les jurons s'envolaient de sa bouche,
Hänen suustaan pulppusi kirosanoja,
The step is therefore rather short to purely mental subjects such as in (35).
(35)
Swedish:
English:
German:
French:
Finnish:
och för ett ögonblick for tanken att han kunde ha rätt genom
hennes huvud. MF
and the thought that he might be right raced through her
mind.
und für einen Augenblick schoß ihr der Gedanke durch den
Kopf, daß er recht haben könnte.
espace d'un instant, la pensée qu'il pouvait avoir raison lui
traversa l'esprit.
ja hetken Hanna ajatteli, että hän saattoi olla oikeassa.
In metaphorical uses such as in (35), where the subject refers to a mental
concept such as ‘thought’, the association to violence or rapidity is still
190
present and it is also reflected in the translations except for in Finnish, where
ajatella ‘think’ is used.
Non-prototypical vehicle
Kalle for på skidor.
Charlie went on skis.
Subject: Vehicle
Bussen for iväg.
The bus left.
TRAVEL IN VEHICLE
Kalle for till Paris.
Charlie went to Paris.
TRAVEL FAST & VIOLENTLY & WITHOUT CONTROL
Subject:
Human
Bodypart
Kalle for av
gungan.
Charlie
flew off the
swing.
Handen for
upp till
munnen. His
hand shot up
to his mouth.
Human subject:
Self-propelled
motion
Kalle for omkring. Charlie
rushed around.
Attack
Kalle for på
Olle.
Charlie flew at
Olle.
Physical
object
Rullgardinen
for upp.
The blind flew
up.
Perceptual
Mental
En rysning for
längs
ryggraden.
A shudder
went down her
spine.
En tanke for
genom huvudet.
A thought raced
through my
head.
Inner speech
Limb movement
Kalle for med
handen över
pannan. Charlie
passed his hand
over his forehead.
Treatment
Kalle for hårt
fram med sina
anställda.
Charlie gave his
employees a
rough time.
Perceptual
activity
Kalle for med
blicken runt
väggarna. Charlie
passed his eyes
around the walls.
Uncontrolled,
abstract motion
Kalle for illa av
behandlingen.
Charlie fared
badly from the
treatment.
Fan också, for
det genom mitt
huvud.
Shit! It flashed
through my
head.
Verbal communication
Kalle for med
osanning.
Charlie told
lies.
Figure 5: The meaning pattern of fara.
With a human subject, the verb has a number of specialized meanings which
are given at the bottom of the figure (without any intention of showing in
191
detail how these meanings are interrelated.) The majority of these meanings
refer to various types of self-propelled but relatively uncontrolled and
violent actions such as: Kalle for på Olle. ‘Charlie flew at Olle’ and
somewhat more abstractly: Kalle for hårt fram med sina anställda. ‘Charlie
gave his employees a rough time.’ There is also a metaphorically based
expression shown in (36) where the human subject is completely out of
control: fara väl/illa av. This is one of the few cases where English can use
the cognate verb fare well/badly from, although this is a slightly archaic use
in English.
(36)
Då begrep Mattis att den stackarn inte for väl av för mycket larm, och
han teg motvilligt. AL
At last Matt realized that too much noise would not do the poor fellow
any good, and he fell into unwilling silence.
The metaphor is a variation on the theme LIFE IS A JOURNEY and the
event structure metaphor (Lakoff 1993). What the phrase fara väl/illa
conjures up is someone drifting through life meeting good or bad things
without being able to control the flow of events. In the translation, the
human being is even formally the object that ‘the noise’ would ‘do’
something to.
The frequencies of the various uses of fara in the tagged version of the
Parole corpus are shown in table 4. Travel in Vehicle is dominant and
accounts for roughly 55%. This is parallel to åka except that the dominance
was more pronounced for that verb, 89%. The verb fara actually has a more
complex meaning pattern than åka and the analysis presented here is not
exhaustive.
Historically, the meaning pattern of fara in present-day Swedish is the
result of specialization. Once fara had a more general meaning as a motion
verb, but today the meaning ‘travel in a vehicle’ is clearly dominant. The
rest of the uses of the verb to a great extent form a large set of phraseological
units that share a schematic meaning ‘travel fast & violently & without
control’ which is also metaphorically extended to various mental and other
abstract phenomena.
192
Human subject:
Travel in Vehicle
Other Human Motion
Verbal communication
Fara illa(/väl)*
Non-human subject
Bodypart
Vehicle as Subject
Other Concrete Subject
Mental subject
Various Other Cases
592
86
17
100
55%
18
36
76
32
110
1067
TOTAL
Table 4: Uses of fara in the Swedish Parole corpus. (*A few of these have a
non-human subject.)
4.3 The Verb Resa
The verb resa is primarily used about a journey covering a relatively long
distance and/or requiring special preparations. Its most direct equivalent in
English is the verb travel, but the nuclear verb go is also quite frequent as a
translation for this meaning. As can be observed in (37), all the MPC
languages have at least one special verb that corresponds relatively directly
to resa and this is the most frequent translation of resa as a verb of traveling
except in French according to table 3. In French, verbs of departure
dominate as translations. (There are, however, only 20 occurrences of resa
as a verb of traveling in the MPC. )
(37)
Swedish:
English:
German:
French:
Finnish:
Han reser runt i världen HM
He travels all over the world
Er reist in der ganzen Welt umher
Il voyage dans le monde entier
Hän matkustelee ympäri maailmaa
What is notable about resa is that it has two prototypes that synchronically
seem to be completely unrelated apart from referring to motion. As an
intransitive verb it means ‘travel’ as we have just seen. However, used as a
transitive verb, resa means ‘raise’, ‘cause to go up’, ‘cause to stand up’.
(38)
Sedan tog han Robert Åkerblom i armen och reste honom upp. HM2
Then he took Robert Åkerblom by the arm and helped him to his feet.
This meaning is closely related to the meaning of the reflexive form of this
verb resa sig, which means ‘stand up’, ‘rise’ and is very frequent as a
193
postural verb. In many cases it is interchangeable with ställa sig up ‘stand
up’ but it may also be used about rising from a lying to a sitting position as
an alternative to Swedish sätta sig upp ‘sit up’. The reflexive forms of resa
are usually translated by one of the expressions rise, get up or stand up in
English and to the corresponding expressions in the other languages.
(39)
Swedish:
English:
German:
French:
Finnish:
Johan reste sig. KE
Johan got up.
Johan stand auf.
Johan se leva.
Johan nousi.
The use as a postural verb is actually the most frequent use in present-day
Swedish, much more frequent than the transitive form and than resa as a
verb of traveling. The postural meaning can be extended to inanimate
subjects and then describes apparent motion as in (40).
(40)
Swedish:
English:
German:
French:
Finnish:
Det väldiga matsalsbordet reser sig över mitt huvud, IB
The huge dining-room table towers above me
Der gewaltige Eßzimmertisch erhebt sich über meinem Kopf,
L'immense table de la salle à manger s'élève au-dessus de ma
tête,
Ruokasalin valtava pöytä kohoaa pääni yläpuolelle,
Transitive resa can be extended to building (resa ett tempel ‘erect a temple’)
and related types of production as in (41).
(41)
Vid Gamla Uppsala och Vendel restes högar över bygdekungar, medan
andra jordades i sina skepp.AA
At Gamla Uppsala and Vendel mighty burial mounds were raised over
the local kings, while others were interred in their ships.
No closer semantic relationship, however, is perceived between resa as a
verb of traveling and the other meanings of resa. One possibility would be to
regard this as a case of homonymy, but there are no formal signs of this
since all the inflected forms are shared. Whatever solution is chosen with
respect to homonymy, it is justified (at least synchronically) to count two
unrelated prototypes for the meaning of resa as in figure 6.
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TRAVEL IN A
VEHICLE
CAUSE TO
MOVE UP
Jan reste till
Paris.
Jan went to
Paris.
Jan reste
majstången.
Jan raised the
maypole.
Building
Mental
Jan reste ett
tempel.
Jan erected a
temple.
Jan reste
frågan.
Jan raised the
question.
POSTURAL
Jan reste sig.
Jan got(stood)
up.
Apparent
motion
Ett slott reser
sig på bergets
krön.
A castle rises
up (looms,
towers) atop
the hill.
Figure 6: Split prototypes. Relationships between the major meanings of
resa ‘travel; and ‘raise, rise’.
The transitive and reflexive forms of the verb have a number of secondary
meanings only some of which are represented in the figure, since it would
take us too far from the topic of this paper to account for these meanings in
detail. With certain mental nouns as object, the meaning of the verb is ‘move
a mental object up to a conscious level’ (a variation on the metaphor
CONSCIOUS IS UP. See Lakoff & Johnson 1980, 15)
(42)
Mannen, en framgångsrik, betrodd och uppmärksammad Herrens tjänare,
reste onaturliga
The man, a successful and trusted servant of the Lord who people made
much of, placed
(43)
När man letar utmärkande drag hos ett helt folk hittar man idel
motsägelser, varje påstående reser opposition.IU Lit. ‘raises opposition’
Fumbling after characteristics
of a whole people one finds nothing but contradictions, every
statement calls up its opposite.
195
Thus, as was the case with the other verbs of traveling åka and fara, the use
of resa as a verb of traveling is isolated from the rest of the uses of the verb
which form a semantic network. In this case, however, there is a complete
split.
5
The Motion-in-Vehicle Verbs in Swedish FrameNet
The account so far has been focused on individual verbs. In this section, the
place of the motion-in-vehicle verbs in a general model of the lexicon will
be discussed based on FrameNet. Unless otherwise stated, only the meanings
related to the use of the verbs as motion-in-vehicle verbs will be considered.
According to the approach to semantics known as frame semantics (Fillmore
1985), verbs (and other relational words) evoke frames – schematic
structures of recurring situations. This theory is the foundation of FrameNet,
a comprehensive lexical semantic database of English (see Fillmore et al
2003 for a general description). The following is based on material from:
http://framenet.icsi.berkeley.edu. The motion frame is defined in the
following way: Some entity (Theme) starts out in one place (Source) and
ends up in some other place (Goal), having covered some space between the
two (Path). A simple example would be: Peter (Theme) fell off the roof
(Source). The frames that inherit the general Motion frame add some
elaboration to this simple idea. Inheriting frames can add Goal-profiling
(arrive, reach), Source-profiling (leave, depart), or Path-profiling (traverse,
cross), or aspects of the manner of motion (run, jog). Source-profiling is
characteristic of what was referred to above as the verbs of departure.
Another elaboration is represented by the frame Self_motion in which the
central frame element is the Self_mover , a living being which moves under
its own power in a directed fashion, i.e. along what could be described as a
Path , with no separate vehicle. A typical example in Swedish would be Per
(Self-mover) gick till stationen (Goal) ‘Per walked to the station’. In
Swedish, the subject of gå in contrast to English go always is a Self-mover,
if it refers to a human.
FrameNet provides an interface to the syntactic realization such as the
argument structure of verbs. This is shown for köra ‘drive’ in table 5. In its
basic meaning, köra evokes the frame Operate_vehicle. The words in this
frame describe motion involving a Vehicle and someone who controls it, the
Driver. Some words normally allow the Vehicle to be expressed as a
separate constituent. Example: Tim [Driver] DROVE his car [Vehicle] all
the way across North America [Path]. The syntactic realization of the frame
elements can be described with respect to Phrase types (NP, PP...) and
grammatical functions (subject, object, adjunct…). As can be observed in
table 5, the subject slot can be filled by the frame elements Driver or and
Vehicle. (The passive allows further options but these follow from general
syntactic rules.) The object slot can be filled by Vehicle, Passenger or Cargo.
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Grammatical
Relations
Phrase
Structure
Frame
elements
Frame
elements
Frame
elements
Subject
Object
Adjuncts
(NP)
(PPn)
Maria
körde
in
‘Maria drove (‘in’) the car into the garage’
Driver
bilen
i garaget
Vehicle
Goal
Maria
barnen
från
skolan
NP
Verb
körde
(Particle)
hem
Lit. ‘Maria drove home the kids from school’’
Driver
Passenger
Source
Maria
körde
hem
möblerna
Lit. ‘Maria drove home the furniture in her Volvo’
Driver
Cargo
i sin volvo
Bilen
körde
ner
Lit. ‘The car drove down into the ditch’
Vehicle
i diket.
Vehicle
Goal
Table 5: Frame elements of köra and their syntactic realization.
Frame elements:
Driver: The being, typically human, that controls the Vehicle as it moves
Vehicle: The means of conveyance controlled by the Driver
Cargo/Passenger: The goods or people being moved by a Driver in a Vehicle
The frame elements evoked by the verbs åka and resa are shown in table 6.
In FrameNet, there is a frame Ride_vehicle defined as “a Theme is moved
by a Vehicle which is not directly under its power”. When åka is used as a
motion-in-vehicle verb, a human subject is normally interpreted as an
intentional agent. For that reason, another frame element is preferred:
Passenger defined as a person being moved by a Driver in a Vehicle. Theme
is reserved for the case when the subject refers to a person who is totally out
of control (or to an inanimate argument). A vehicle can be specified directly
after the verb åka in Swedish. Since the vehicle in this position is realized as
a bare noun, it can be regarded as a particle. When the noun is modified, it
usually appears as an adjunct in a prepositional phrase (e.g. i sin pappas bil
‘in his dad’s car’). The verb resa evokes the Travel frame: „a Traveler goes
on a journey, an activity, generally planned in advance”. The vehicle can
only be specified as an adjunct in a prepositional phrase with med ‘with’
(e.g. med tåg ‘by train’).
197
Phrase
structure
Frame
elements
Frame
elements
Frame
elements
NP
Verb
(Particle)
Jan
åkte
bil
Lit. ‘Jan went (by) car to school’’
Passenger
Vehicle
Jan
åkte
‘Jan flew off the swing’
Theme
av
Bilen
åkte
in
Lit. ‘The car went in into the tunnel’
Vehicle
(PPn)
till skolan
Goal
gungan
Source
i tunneln
Goal
Familjen
reste
upp
till fjällen
Lit. ‘The family traveled up to the mountains by bus.’
Traveller
Goal
med buss.
Vehicle
Table 6: Frame elements of åka and resa and their syntactic realization.
As shown in table 7, the verbs åka, fara and resa can all evoke the Departing
frame defined as: „An object (the Theme) moves away from a Source”.
NP
Subject
Theme
Ann
V
åkte
for
reste
‘Ann went (away)/left’
(Particle)
(iväg/bort)
Table 7: The Departing frame.
FrameNet is well suited to model the interface between semantic
(conceptual) structure and syntax (in particular the argument structure). The
account given in this section does not deal with phenomena that apply to
motion verbs in general, in particular the wide range of frame elements
evoked by the general motion frame such as Source, Path, Goal and
Distance. In FrameNet such elements are inherited from the more general
frame. Some general problems remain to be solved, in particular the
198
description of the interaction between motion verbs and spatial verbal
particles (see Viberg 2007 for a brief discussion). As has been observed
several times above, French tends to use directional verbs without any
indication of manner, where Swedish uses a motion-in-vehicle verb in
combination with a spatial particle.
6
Conclusion
The verbs describing motion in a vehicle form a (sub-)field in the larger
semantic field of motion verbs. This paper has dealt with patterns of
differentiation, i.e. field internal contrasts between the verbs in the field, and
with patterns of polysemy of the individual verbs which extend into a
number of other semantic fields.
The differentiation pattern was studied from a contrastive perspective. It is
instructive to look at the differences that were found from two different
angles: inventories and usage patterns. The comparison of the inventories
describes the number of semantic contrasts that can be expressed. All the
languages studied had verbs describing motion in a vehicle but varied with
respect to the number of field internal contrasts that were lexicalized as
different verbs. Thus, there were interesting differences even with respect to
the inventories. The study of the usage patterns in the corpora, however,
presented much more dramatic differences. As a translation of åka and fara,
English tended to use the nuclear verb go which is completely unmarked for
manner of motion, whereas Finnish favored a verb of departure (lähteä
‘leave’) and French primarily used directional verbs or verbs of departure.
Such findings with respect to differences in usage patterns are among the
key results of corpus-based contrastive studies. One limitation of the present
study is that primarily one direction of translation was studied: from
Swedish into other languages but it is not to be expected that these
differences will completely disappear if the study is extended to include
originals in the other languages translated into Swedish. (In other studies,
this type of comparison has already been done especially for
English/Swedish.)
The study of the patterns of polysemy of the Swedish motion-in-vehicle
verbs pointed to an interesting general trend. In several cases, the semantic
extension proceeded from power and control towards passivity and/or lack
of control. Perhaps this finding can be related to the rapid change of the
means of transportation that has taken place the last 150 years or so, from
the control of domestic riding and draft animals with a will of their own to
the use of more and more automated cars and modern passenger traffic. In
old times, traveling tended to require greater amounts of control and effort
(cf. French travail ‘work’, which is closer to the original meaning than its
English cognate travel). More detailed comparisons with other languages are
required to decide whether the development in Swedish represents a general
trend or is more language specific. What is perfectly clear already from the
present study is that there has been rapid semantic restructuring resulting in
199
differences between the closely related Germanic languages. Verbs like
Dutch rijden and Danish køre still have a form that is very close to Swedish
rida and köra in spite of their wide semantic extensions. One of the
interesting results of the study of rather closely related languages is the
observation that semantic change can proceed relatively rapidly.
References
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201
The Automatic Translation of Film Subtitles
A Machine Translation Success Story?
Martin Volk
Stockholm University
Department of Linguistics
1
University of Zurich
Institute of Computational
Linguistics
Introduction
Every so often one hears the complaint that 50 years of research in Machine
Translation (MT) has not resulted in much progress, and that current MT systems are still unsatisfactory. A closer look reveals that web-based generalpurpose MT systems are used by thousands of users every day. And, on the
other hand, special-purpose MT systems have been in long-standing use and
work successfully in particular domains or for specific companies.
This paper investigates whether the automatic translation of film subtitles
can be considered a machine translation success story. We describe various
projects on MT of film subtitles and contrast them to our own project in this
area. We argue that the text genre “film subtitles” is well suited for MT, in particular for Statistical MT. But before we look at the translation of film subtitles
let us retrace some other MT success stories.
Hutchins (1999) lists a number of successful MT systems. Amongst them
is Météo, a system for translating Canadian weather reports between English
and French which is probably the most quoted MT system in practical use.
References to Météo usually remind us that this is a “highly constrained sublanguage system”. On the other hand there are general purpose but customerspecific MT systems like the English to Spanish MT system at the Pan American Health Organization or the PaTrans system which Hutchins (1999) calls
“possibly the best known success story for custom-built MT”. PaTrans was
developed for LingTech A/S to translate English patents into Danish.
Earlier Whitelock and Kilby (1995) had called the METAL system “a success story in the development of MT” (p. 198). METAL is mentioned as “successfully used at a number of European companies” (by that time this meant a
few dozen installations in industry, trade or banking). During the same time the
European Union has been successfully using a customized version of Systran
for its translation service but also later for online access by all its employees.
202
1
Broad coverage systems like METAL and Systran have always resulted in a
translation quality that required post-editing before publications.
Attempts to curb the post-editing by pre-editing or constraining the source
documents have gone under the name of controlled language MT. Hutchins
(1999) mentions controlled language MT (e.g. at the Caterpillar company) as
an example of successful employment of MT. This is an area where part of the
pioneering work was done at Uppsala University by Anna Sågvall Hein and
her group (Almqvist and Sågvall Hein, 1996), including the development of
controlled Swedish for the automobile industry. This research subsequently led
to a competitive MT system for translating from Swedish to English (Sågvall
Hein et al., 2002).
The claim that web-based machine translation is a success is based on the
fact that it is used by large numbers of users. Critics do not subscribe to
this argument as long as the translation quality is questionable. Still, popular services including Systran (www.systran.co.uk with 14 source languages)
and Google (www.google.com/translate_t with 21 language pairs) cover major
Western languages like English, Spanish and French, but also Arabic and Chinese. On the other hand there are providers that have successfully occupied
niche language pairs like Danish to English (Bick, 2007).
So we see that MT success stories vary considerably. We regard the following criteria as the main indicators of success:
1. A large user base (this criterion is used in web-based MT services for
the general public)
2. Customer satisfaction (this criterion is used in customer-specific MT
systems and usually based on improved productivity and return on investment)
3. Long-term usage of the MT system
We will check which of these criteria apply to the automatic translation of
film subtitles.
2
Characteristics of Film Subtitles
When films are shown to audiences in language environments that differ from
the language spoken in the film, then some form of translation is required.
Larger markets like Germany and France typically use dubbing of foreign
films so that it seems that the actors are speaking the local language. Smaller
countries often use subtitles. Pedersen (2007) discusses the advantages and
drawbacks of both methods.
Foreign films and series shown in Scandinavian TV are usually subtitled
rather than dubbed. Therefore the demand for Swedish, Danish, Norwegian
and Finnish subtitles is high. These subtitles are meant for the general public
203
in contrast to subtitles that are specific for the hearing impaired which often
include descriptions of sounds, noises and music. Subtitles also differ with
respect to whether they are produced online (e.g. in live talkshows or sport
reports) or offline (e.g. for pre-produced series). This paper focuses on general
public subtitles that are produced offline.
In our machine translation project, we use a parallel corpus of Swedish,
Danish and Norwegian subtitles. The subtitles in this corpus are limited to 37
characters per line and usually to two lines.1 Depending on their length, they
are shown on screen between 2 and 8 seconds. Subtitles typically consist of
one or two short sentences with an average number of 10 tokens per subtitle
in our corpus. Sometimes a sentence spans more than one subtitle. It is then
ended with a hyphen and resumed with a hyphen at the beginning of the next
subtitle. This occurs about 35.7 times for each 1000 subtitles in our corpus.
Example 1 shows a human-translated pair of subtitles that are close translation correspondences although the Danish translator has decided to break the
two sentences of the Swedish subtitle into three sentences.2
(1)
SV: Det är slut, vi hade förfest här. Jätten drack upp allt.
DA: Den er væk. Vi holdt en forfest. Kæmpen drak alt.
EN: It is gone. We had a pre-party here. The giant drank it all.
In contrast, the pair in 2 exemplifies a slightly different wording chosen by
the Danish translator.
(2)
SV: Där ser man vad framgång kan göra med en ung person.
DA: Der ser man, hvordan succes ødelægger et ungt menneske.
EN: There you see, what success can do to a young person / how
success destroys a young person.
This paper can only give a rough characterization of subtitles. A more comprehensive description of the linguistic properties of subtitles can be found in
(de Linde and Kay, 1999). Gottlieb (2001) and Pedersen (2007) describe the
peculiarities of subtitling in Scandinavia.
3
Approaches to the Automatic Translation of Film
Subtitles
In this section we describe other projects on the automatic translation of subtitles. We distinguish between rule-based, example-based, and statistical approaches.
1
Although we are working on both Swedish to Danish and Swedish to Norwegian MT of
subtitles, this paper focuses on translation from Swedish to Danish. The issues for Swedish to
Norwegian are the same to a large extent.
2
In this example and in all subsequent subtitle examples the English translations were added
by the author.
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3.1
Rule-based MT of Film Subtitles
Popowich et al. (2000) provide a detailed account of a MT system tailored towards the translation of English subtitles into Spanish. Their approach is based
on a MT paradigm which relies heavily on lexical resources but is otherwise
similar to the transfer-based approach. A unification-based parser analyzes
the input sentence (including proper-name recognition), followed by the lexical transfer which provides the input for the generation process in the target
language (including word selection and correct inflection).
Popowich et al. (2000) mention that the subtitle domain has certain advantages for MT. According to them it is advantageous that output subtitles can
and should be grammatical even if the input sometimes is not. They argue that
subtitle readers have only a limited time to perceive and understand a given
subtitle and that therefore grammatical output is essential. And they follow
the strategy that “it is preferable to drop elements from the output instead of
translating them incorrectly” (p. 331). This is debateable and opens the door
for incomplete output.
Although Popowich et al. (2000) call their system “a hybrid of both statistical and symbolic approaches” (p. 333), it is a symbolic system by today’s
standards. The statistics are only used for efficiency improvements but are
not at the core of the methodology. The paper was published before automatic evaluation methods were invented. Instead Popowich et al. (2000) used
the classical evaluation method where native speakers were asked to judge the
grammaticality and fidelity of the system. These experiments resulted in “70%
of the translations ... be ranked as correct or acceptable, with 41% being correct” which is an impressive result. Whether this project can be regarded as
a MT success story depends on whether the system was actually employed in
production. This information is not provided in the paper.
Melero et al. (2006) combined Translation Memory technology with Machine Translation, which looks interesting at first sight. But then it turns out
that their Translation Memories for the language pairs Catalan-Spanish and
Spanish-English were not filled with subtitles but rather with newspaper articles and UN texts. They don’t give any motivation for this. And disappointingly they did not train their own MT system but rather worked only with freeaccess web-based MT systems (which we assume are rule-based systems).
They showed that a combination of Translation Memory with such webbased MT systems works better than the web-based MT systems alone. For
English to Spanish translation this resulted in an improvement of around 7
points in BLEU scores (Papineni et al., 2001) but hardly any improvement at
all for English to Czech.
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3.2
Example-based MT of Film Subtitles
Armstrong et al. (2006) “ripped” subtitles (40,000 sentences) German and English as training material for their Example-based MT system and compared
the performance to the same amount of Europarl sentences (which have more
than three times as many tokens!). Training on the subtitles gave slightly better
results when evaluating against subtitles, compared to training on Europarl and
evaluating against subtitles. This is not surprising, although the authors point
out that this contradicts some earlier findings that have shown that heterogeneous training material works better.
They do not discuss the quality of the ripped translations nor the quality of
the alignments (which we found to be a major problem when we did similar
experiments with freely available English-Swedish subtitles).
The BLEU scores are on the order of 11 to 13 for German to English (and
worse for the opposite direction). These are very low scores. They also conducted user evaluations with 4-point scales for intelligibility and accuracy.
They asked 5 people per language pair to rate a random set of 200 sentences of
system output. The judges rated English to German translations higher than the
opposite direction (which contradicts the BLEU scores). Owing to the small
scale of the evaluation, however, it seems premature to draw any conclusions.
3.3
Statistical MT of Film Subtitles
Descriptions of Statistical MT systems for subtitles are practically non-existent
probably due to the lack of freely available training corpora (i.e. collections
of human-translated subtitles). Both Tiedemann (2007) and Lavecchia et al.
(2007) report on efforts to build such corpora with alignment on the subtitles.
Tiedemann (2007) works with a huge collection of subtitle files that are
available on the internet at www.opensubtitles.org. These subtitles have been
produced by volunteers in a great variety of languages. But the volunteer effort
also results in subtitles of often dubious quality (they include timing, formatting, and linguistic errors). The hope is that the enormous size of the corpus
will supersede the noise in practical applications. The first step then is to align
the files across languages on the subtitle level. The time codes alone are not
sufficient as different (amateur) subtitlers have worked with different time offsets and sometimes even different versions of the same film. Still, Tiedemann
(2007) shows that an alignment approach based on time overlap combined with
cognate recognition is clearly superior to pure length-based alignment. He has
evaluated his approach on English, German and Dutch. His results of 82.5%
correct alignments for Dutch-English and 78.1% correct alignments for DutchGerman show how difficult the alignment task is. And a rate of around 20%
incorrect alignments will certainly be problematic when training a Statistical
MT system on these data.
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Lavecchia et al. (2007) also work with subtitles obtained from the internet.
They work on French-English subtitles and use a method which they call Dynamic Time Warping for aligning the files across the languages. This method
requires access to a bilingual dictionary to compute subtitle correspondences.
They compiled a small test corpus consisting of 40 subtitle files, randomly
selecting around 1300 subtitles from these files for manual inspection. Their
evaluation focused on precision while sacrificing recall. They report on 94%
correct alignments when turning recall down to 66%. They then go on to use
the aligned corpus to extract a bilingual dictionary and to integrate this dictionary in a Statistical MT system. They claim that this improves the MT system
with 2 points BLEU score (though it is not clear which corpus they have used
for evaluating the MT system).
This summary indicates that most work on the automatic translation of film
subtitles with Statistical MT is still in its infancy. Our own efforts are larger
and have resulted in a mature MT system. We will report on them in the
following section.
4
The Stockholm MT System for Film Subtitles
We are building a Machine Translation system for translating film subtitles
from Swedish to Danish (and Swedish to Norwegian) in a commercial setting.
Some of this work has been described earlier by Volk and Harder (2007).
Most films are originally in English and receive Swedish subtitles based on
the English video and audio (sometimes accompanied by an English manuscript). The creation of the Swedish subtitle is a manual process done by specially trained subtitlers following company-specific guidelines. In particular,
the subtitlers set the time codes (beginning and end time) for each subtitle.
They use an in-house tool which allows them to attach the subtitle to specific
frames in the video.
The Danish translator subsequently has access to the original English video
and audio but also to the Swedish subtitles and the time codes. In most cases
the translator will reuse the time codes and insert the Danish subtitle. She can,
on occasion, change the time codes if she deems them inappropriate for the
Danish text.
Our task is to produce Danish and Norwegian draft translations to speed up
the translators’ work. This project of automatically translating subtitles from
Swedish to Danish and Norwegian benefits from three favorable conditions:
1. Subtitles are short textual units with little internal complexity (as described in section 2).
2. Swedish, Danish and Norwegian are closely related languages.
3. We have access to large numbers of Swedish subtitles and human-translated Danish and Norwegian subtitles. Their correspondence can easily
207
be established via the time codes which leads to an alignment on the
subtitle level.
But there are also aspects of the task that are less favorable. Subtitles are not
transcriptions, but written representations of spoken language. As a result the
linguistic structure of subtitles is closer to written language than the original
(English) speech, and the original spoken content usually has to be condensed
by the Swedish subtitler.
The task of translating subtitles also differs from most other machine translation applications in that we are dealing with creative language, and thus we
are closer to literary translation than technical translation. This is obvious
in cases where rhyming song-lyrics or puns are involved, but also when the
subtitler applies his linguistic intuitions to achieve a natural and appropriate
wording which blends into the video without disturbing. Finally, the language
of subtitling covers a broad variety of domains from educational programs on
any conceivable topic to exaggerated modern youth language.
We have decided to build a statistical MT (SMT) system in order to shorten
the development time (compared to a rule-based system) and in order to best
exploit the existing translations. We have trained our SMT system by using
GIZA++ (Och and Ney, 2004)3 for the alignment, Thot (Ortiz-Martínez et al.,
2005)4 for phrase-based SMT, and Phramer5 as the decoder.
We will first present our setting and our approach for training the SMT system and then describe the evaluation results.
4.1
Swedish and Danish in Comparison
Swedish and Danish are closely related Germanic languages. Vocabulary and
grammar are similar, however orthography differs considerably, word order
differs somewhat and, of course, pragmatics avoids some constructions in one
language that the other language prefers. This is especially the case in the
contemporary spoken language, which accounts for the bulk of subtitles.
One of the relevant differences for our project concerns word order. In
Swedish the verb takes non-nominal complements before nominal ones, where
in Danish it is the other way round. The core problem can be seen in example
3 where the verb particle ut immediately follows the verb in Swedish but is
moved to the end of the clause in Danish.
(3)
SV: Du häller ut krutet.
DA: Du hælder krudtet ud.
EN: You are pouring out the gunpowder.
A similar word order difference occurs in positioning the negation adverb
(SV: inte, DA: ikke). Furthermore, Danish distinguishes between the use of
3
GIZA++ is accessible at http://www.fjoch.com/ GIZA++.html
Thot is available at http://thot.sourceforge.net/
5
Phramer was written by Marian Olteanu and is available at http://www.olteanu.info/
4
208
der (EN: there) and det (EN: it) but Swedish does not. Both Swedish and
Danish mark definiteness with a suffix on nouns, but Danish does not have the
double definiteness marking of Swedish.
4.2
Our Subtitle Corpus
Our corpus consists of TV subtitles from soap operas (like daily hospital series), detective series, animation series, comedies, documentaries, feature films
etc. In total we have access to more than 14,000 subtitle files (= single TV programmes) in each language, corresponding to more than 5 million subtitles
(equalling more than 50 million words).
When we compiled our corpus we included only subtitles with matching
time codes. If the Swedish and Danish time codes differed more than a threshold of 15 TV-frames (0.6 seconds) in either start or end-time, we suspected that
they were not good translation equivalents and excluded them from the subtitle
corpus. In this way we were able to avoid complicated alignment techniques.
Most of the resulting subtitle pairs are high-quality translations of one another
thanks to the controlled workflow in the commercial setting.
In a first profiling step we investigated the vocabulary size of the corpus.
After removing all punctuation symbols and numbers we counted all word
form types. We found that the Swedish subtitles amounted to around 360,000
word form types. Interestingly, the number of Danish word form types is about
5.5% lower, although the Danish subtitles have around 1.5% more tokens. We
believe that this difference may be an artifact of the translation direction from
Swedish to Danish which may lead the translator to a restrictive Danish word
choice.
Another interesting profiling feature is the repetitiveness of the subtitles. We
found that 28% of all Swedish subtitles in our training corpus occur more than
once. Half of these recurring subtitles have exactly one Danish translation.
The other half have two or more different Danish translations which are due
to context differences combined with the high context dependency of short
utterances and the Danish translators choosing less compact representations.
From our subtitle corpus we chose a random selection of files for training
the translation model and the language model. We currently use 4 million subtitles for training. From the remaining part of the corpus, we selected 24 files
(approximately 10,000 subtitles) representing the diversity of the corpus from
which a random selection of 1000 subtitles was taken for our test set. Before
the training we tokenized the subtitles (e.g. separating punctuation symbols
from words), converting all uppercase words into lower case, and normalizing
punctuation symbols, numbers and hyphenated words.
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4.3
Unknown Words
Although we have a large training corpus, there are still unknown words (words
not seen in the training data) in the evaluation data. They comprise proper
names of people or products, rare word forms, compounds, spelling deviations
and foreign words. Proper names need not concern us in this context since the
system will copy unseen proper names (like all other unknown words) into the
Danish output, which in almost all cases is correct.
Rare word forms and compounds are more serious problems. Hardly ever
do all forms of a Swedish verb occur in our training corpus (regular verbs have
7 forms). So even if 6 forms of a Swedish verb have been seen frequently
with clear Danish translations, the 7th will be regarded as an unknown if it is
missing in the training data.
Both Swedish and Danish are compounding languages which means that
compounds are spelled as orthographic units and that new compounds are dynamically created. This results in unseen Swedish compounds when translating new subtitles, although often the parts of the compounds were present in
the training data. We therefore generate a translation suggestion for an unseen
Swedish compound by combining the Danish translations of its parts.
Variation in graphical formatting also poses problems. Consider spell-outs,
where spaces, commas, hyphens or even full stops are used between the letters
of a word, like “I will n o t do it”, “Seinfeld” spelled “S, e, i, n, f, e, l , d”
or “W E L C O M E T O L A S V E G A S”, or spelling variations like
ä-ä-älskar or abso-jävla-lut which could be rendered in English as lo-o-ove or
abso-damned-lutely. Subtitlers introduce such deviations to emphasize a word
or to mimic a certain pronunciation. We handle some of these phenomena in
pre-processing, but, of course, we cannot catch all of them due to their great
variability.
Foreign words are a problem when they are homographic with words in
the source language Swedish (e.g. when the English word semester = “university term” interferes with the Swedish word semester which means “vacation”). Example 4 shows how different languages (here Swedish and English)
are sometimes intertwined in subtitles.
(4)
SV: Hon gick ut Boston University’s School of the Performing Arts-och hon fick en dubbelroll som halvsystrarna i “As the World Turns”.
EN: She left Boston University’s School of the Performing Arts and she
got a double role as half sisters in “As the World Turns”.
4.4
Evaluating the Performance of the Stockholm MT System
We first evaluated the MT output against a left-aside set of previous human
translations. We computed BLEU scores of around 57 in these experiments.
In addition we computed the percentage of exactly matching subtitles against
a previous human translation (How often does our system produce the exact
210
Crime series
Comedy series
Car documentary
Average
Exact matches
15.0%
9.1%
3.2%
9.1%
Levenshtein-5 matches
35.3%
30.6%
22.8%
21.6%
BLEU
63.9
54.4
53.6
57.3
Table 1: Evaluation Results against a Prior Human Translation.
same subtitle as the human translator?), and we computed the percentage of
subtitles with a Levenshtein distance of up to 5 which means that the system
output has an editing distance of at most 5 basic character operations (deletions, insertions, substitutions) from the human translation.
We decided to use a Levenshtein distance of 5 as a threshold value as we
consider translations at this edit distance from the reference text still to be
“good” translations. Such a small difference between the system output and the
human reference translation can be due to punctuation, to inflectional suffixes
(e.g. the plural -s in example 5 with MT being our Danish system output and
HT the human translation) or to incorrect pronoun choices.
(5)
MT: Det gør ikke noget. Jeg prøver gerne hotdog med kalkun HT: Det gør ikke noget. Jeg prøver gerne hotdogs med kalkun, EN: That does not matter. I like to try hotdog(s) with turkey.
Table 1 shows the results for three files (selected from different genres), for
which we have prior translations (done independently of our system). We observe between 3.2% and 15% exactly matching subtitles, and between 22.8%
and 35.3% subtitles with a Levenshtein distance of up to 5. Note that the percentage of Levenshtein matches includes the exact matches (which correspond
to a Levenshtein distance of 0).
On manual inspection, however, many automatically produced subtitles that
were more than 5 keystrokes away from the human translations still looked
like good translations. Therefore we conducted another series of evaluations
with translators who were asked to post-edit the system output rather than to
translate from scratch. We made sure that the translators had not translated the
same file before.
Table 2 shows the results for the same three files for which we have one
prior translation. We gave our system output to six translators and obtained six
post-edited versions. Some translators were more generous than others, and
therefore we averaged their scores. When using post-editing, the evaluation
figures are 13.2 percentage points higher for exact matches and 19.5 percentage points higher for Levenshtein-5 matches. It becomes also clear that the
211
Crime series
Comedy series
Car documentary
Average
Exact matches
27.7%
26.0%
13.2%
22.3%
Levenshtein-5 matches
47.6%
45.7%
35.9%
43.1%
BLEU
69.9
67.7
59.8
65.8
Table 2: Evaluation Results averaged over 6 Post-editors.
translation quality varies considerably across film genres. The crime series file
scored consistently higher than the comedy file which in turn was clearly better
than the car documentary.
There are only few other projects on Swedish to Danish Machine Translation
(and we have not found a single one on Swedish to Norwegian). Koehn (2005)
trained his system on a parallel corpus of more than 20 million words from
the European parliament. In fact he trained on all combinations of the 11
languages in the Europarl corpus. Koehn (2005) reports a BLEU score of 30.3
for Swedish to Danish translation which ranks somewhere in the middle when
compared to other language pairs from the Europarl corpus. The worst score
was for Dutch to Finnish (10.3) and the best for Spanish to French translations
(40.2). The fact that our BLEU scores are much higher even when we evaluate
against prior translations (cf. the average of 57.3 in table 1) is probably due to
the fact that subtitles are shorter than Europarl sentences and perhaps also due
to our larger training corpus.
5
Conclusions
We have sketched the text genre characteristics of film subtitles and shown
that Statistical MT of subtitles leads to good quality when the input is a large
high-quality parallel corpus. We are working on Machine Translation systems
for translating Swedish film subtitles to Danish and Norwegian with very good
results (in fact the results for Swedish to Norwegian are slightly better than for
Swedish to Danish).
We have shown that evaluating the system against independent translations
does not give a true picture of the translation quality and thus of the usefulness
of the system. Evaluation BLEU scores were about 8.5 points higher when we
compared our system output against post-edited translations averaged over six
translators. Exact matches and Levenshtein 5 scores were also clearly higher.
We are dealing with a customer-specific MT system covering a broad set of
textual domains. The customer is satisfied and has recently started to employ
our MT system in large scale production. It is too early to advertise this as
212
an MT success story as the overall productivity increase has not yet been determined. But we believe that our evaluation results are promising and hope
that a future assessment will prove that the deployment of our MT system is
profitable.
6
Acknowledgements
We would like to thank Jörgen Aasa, Søren Harder and Christian Hardmeier
for sharing their expertise, providing evaluation figures and commenting on an
earlier version of the paper.
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