Pre-Proceedings

Pre-Proceedings
7th Educators’ Symposium@MODELS 2011
— Software Modeling in Education —
Pre-Proceedings
edited by
Marion Brandsteidl
TU Wien, Information & Software Engineering Group
Andreas Winter
Carl von Ossietzky Universität Oldenburg, Software Engineering
OLNSE Number 2/2011
September 2011
Oldenburg Lecture Notes in Software Engineering
Oldenburg Lecture Notes
on Software Engineering (OLNSE)
Carl von Ossietzky University Oldenburg
Department for Computer Science
Software Engineering
26111 Oldenburg, Germany
– copyright by authors –
Oct. 18, 2011
EduSymp 2011 Program
09:00 - 10:30
Session 1: Teaching Certain Topics
page
09:00 - 09:05
Opening Remarks
09:05 - 09:40
Guest Speaker: Robert B. France: Teaching Student
Programmers How to Model: Opportunities & Challenges
5
09:40 - 10:05
Avoiding OCL specification pitfalls
Dan Chiorean, Ileana Ober and Vladiela Petrascu.
7
10:05 - 10:30
Teaching MDE through the Formal Verification of Process Models
Benoît Combemale, Xavier Crégut, Arnaud Dieumegard, Marc
Pantel and Faiez Zalila.
10:30 - 11:00
Break
11:00 - 12:30
Session 2: Practical Approaches in Teaching and Teaching
17
in Practice
11:00 - 11:30
Mismatches between industry practice and teaching of modeldriven software development
Jon Whittle and John Hutchinson.
27
11:30 - 12:00
Ready for the Industry: A Practical Approach to Teaching MDE
Gordana Milosavljevic, Igor Dejanovic and Branko Perisic.
31
12:00 - 12:30
Models and Clickers for Teaching Computer Science
Matthias Hauswirth.
41
12:30 - 14:00
Lunch
14:00 - 15:30
Session 3: Teaching approaches und Modeling Skills
14:00 - 14:30
Model Correctness Patterns as an Educational Instrument
Azzam Maraee, Mira Balaban, Arnon Strum and Adiel Ashrov.
45
14:30 - 15:00
Threshold Concepts in Object-Oriented Modelling
Ven Yu Sien and David Weng Kwai Chong.
55
15:00 - 15:30
Teaching Modeling-An Initial Classification of Related Issues
Ludwik Kuzniarz and Jürgen Börstler.
65
15:30 - 16:00
Break
16:00 - 17:30
Session 4: Discussion: Modeling Curriculum
16:00 - 16:20
Position Paper: Software Modelling Education
Martina Seidl and Peter Clarke.
16:20 - 17:20
Discussion: Skills to teach in a Modeling Curriculum
17:20 - 17:30
Wrap up and plans for the next symposium
71
Collocated with the ACM/IEEE International Conference on Model-Driven
Engineering Languages and Systems (MODELS), the Educators’ Symposium
(EduSymp) focuses on the wide topic of software modeling education ranging from
experience reports and case studies to novel pedagogical approaches. MODELS
2011 will host the 7th Educators' Symposium, whose papers are compiled in these
pre-proceedings.
Modeling systems plays an important role in todays software development and
evolution. Modeling provides goal-oriented abstractions in all phases of software
development, which requires deep knowledge on modeling techniques and broad
experiences in applying these techniques. Software Engineering is supported by
various modeling techniques, providing modeling languages, modeling language
definition technologies, and model transformation technologies. Industry and
academia successfully realized expressive modeling and meta-modeling languages
and mature tools for the practical application.
The Educators' Symposium at MODELS focuses on discussing educating these
technologies to software engineers at universities and software industries. Although
most computer science curricula include some education in modeling technologies
and therefore provide the basic building blocks for modeling, meta-modeling, and
model transformation, the whole spectrum of modeling in software engineering is
rarely captured, even a curriculum on modeling is not available to define education
standards in modeling.
EduSymp 2011 received 13 papers, from which 8 were accepted for presentation,
eventually. The papers have passed through a rigorous review process and will be
presented at EduSymp 2011. We are very delighted that Robert France will present
his broad insights in teaching modeling in an interesting keynote on “Teaching
Student Programmers How to Model: Opportunities & Challenges”. This year’s
symposium will also include an intensive discussion on skills and competencies to be
educated in modern modeling education. These discussions will be introduced by a
stimulating position paper by Martina Seidl Peter Clarke on Software Modelling
Education.
The final proceedings of EduSymp 2011 will be published at the Electronic
Communications of the EASST, which will contain reworked and extended versions
of the papers presented in these pre-proceedings.
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Thanks to all authors who considered EduSymp 2011 for sharing and discussing their
thoughts and submitting a paper. Our deepest thanks also go to Robert France,
Martina Seidl and Peter Clarke for supporting EduSymp with their additional
presentations. We would also like to express our gratitude to the program committee
who supported excellent and timely reviews, which will provide significant hints to
improve and extend the already much elaborated submitted papers. The list of the
International Program Committee is shown below:
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Colin Atkinson, University of Mannheim, Germany
Jordi Cabot, University of Nantes, France
Peter J. Clarke, Florida International University, USA
Ira Diethelm, Carl von Ossietzky University, Germany
Jean-Marie Favre, OneTree Technologies, Luxembourg
Robert France, Colorado State University, USA
Michael Godfrey, University of Waterloo, Canada
Martin Gogolla, University of Bremen, Germany
Øhystein Haugen, SINTEF, Norway
Gerti Kappel, Vienna University of Technology, Austria
Ludwik Kuzniarz, Blekinge Institute of Technology, Sweden
Jochen Ludewig, University of Stuttgart, Germany
Karl Reed, La Trobe University, Australia
Jean-Paul Rigault, University of Nice, France
Patricia Roberts, University of Brighton, UK
Martina Seidl, Vienna University of Technology and Johannes Kepler
University of Linz, Austria
Ven Yu Sien, HELP University College, Malaysia
Our thanks also include the additional reviewers (Christina Dörge , Malte Dünnebier
Elena Planas, Lars Hamann, and Manuel Wimmer). Finally, we like to thank the
orgranizers of MODELS 2011 in Wellington for providing brilliant support for
organizing the 7th Educators' Symposium@Models.
October 2011
7th EduSymp 2011
Marion Brandsteidl
Andreas Winter
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Teaching Student Programmers How to Model: Opportunities &
Challenges
Robert B. France1
1
france@cs.colostate.edu
Dept. of Computer Science
Colorado State University
Abstract: In my experience, students with some programming expertise (or students who believe they are programming experts) tend to view software modeling
with great skepticism. They often feel that modeling adds accidental complexity to
the software development process as they perceive it.
While we should acknowledge that there may be some elements of truth in their
views (new methods, tools and techniques do bring additional baggage that can
initially contribute to accidental complexity), we, as educators, should also try to
leverage such skepticism in an opportunistic manner. In this talk I’ll present some
thoughts on how we can leverage such skepticism and also discuss some of the challenges of teaching students how to discover and use ”‘good”’ abstractions in their
models.
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Avoiding OCL specification pitfalls
Dan Chiorean1 , Ileana Ober2 , Vladiela Petraşcu3
1 chiorean@cs.ubbcluj.ro,
Babeş-Bolyai University, Cluj-Napoca, Romania
Université Paul Sabatier, Toulouse, France
3 vladi@cs.ubbcluj.ro, Babeş-Bolyai University, Cluj-Napoca, Romania
2 ober@irit.fr,
Abstract: This paper discusses about teaching software modeling by using OCL
specifications, in the context in which the web represents the main source of information. The raise of the interest for models induced a higher need for clear and
complete specifications. In case of models specified by means of MOF based languages, adding OCL constraints proved to be an interesting answer to this need.
Several OCL examples posted on web include hasty specifications, that are often
dissuasive with respect to complementing models with OCL specification. OCL
beginners, and not only, need to know how to avoid potential specification traps.
Our proposal is based on a clear, unambiguous and complete description of requirements, that represents the first step towards good OCL specifications. The work
highlights several major aspects that need to be understood and complied with to
produce meaningful and efficient OCL specifications. This approach was tested
while teaching OCL at Babes-Bolyai University of Cluj.
Keywords: rigorous modeling, OCL specifications, meaningful specifications, efficient specifications, model understanding
1
Introduction
OCL is a language whose spread has not confirmed the optimistic expectations expressed since
its inclusion as part of UML 1.1, and then as part of all OMG MOF-based modeling languages.
Being much more active in promoting the language compared to its industrial counterpart, the
academic community has published several reviews in this respect, identifying among the causes
of this state of facts the ambiguities and gaps from the language specification, as well as the
immaturity of OCL tools, as opposed to the now classical IDEs (Integrated Development Environments). Although there has been progress in the above mentioned fields, the developers’
feedback is far from satisfactory. One possible reason is given by both the lack of illustrative
examples for the advantages of using OCL, and the availability of a large number of examples
which, at best, cause confusion among readers. An experience of over ten years in teaching OCL
to computer science students (at both bachelor and master levels) has allowed us to conclude
that, besides providing positive recommendations (articles, books, etc..), it is mandatory to warn
potential OCL users (students, in this case) on the pitfalls enclosed by negative examples. As
web users, students are exposed to both clear, well-written documents and to documents containing pitfalls, on whose potential occurrence teachers have the duty of raising warnings. However,
merely showing that particular models or specifications are inadequate or even incorrect with re-
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spect to the purpose they were created for is not enough. Presenting at least one correct solution
and arguing on its advantages is a must.
Complementing models with OCL is meant at eliminating specifications ambiguities, increasing rigor, reaching a full and clear definition of query operations, as well as promoting design by
contract through the specification of pre and post-conditions.
Development of models and applications takes place as an iterative incremental process, which
allows developers to return to earlier stages whenever the case. Enhancing models with OCL
specifications facilitates their deeper understanding, through both rigor and extra detail. Whenever the results of evaluating OCL specifications suggest a model change, this change should only
be done if the new version is more advantageous compared to the previous ones, as a whole. The
use of OCL specifications should contribute to the requirements validation. An application is
considered as finished only when there is full compliance among its requirements, its model, and
itself.
The remaining of this paper is organized as follows. Section 2 explains the reasons why
teaching OCL through examples integrated in models is more advantageous compared to the
classical way of teaching OCL. In Section 3, we argue on the necessity of understanding the
model’s semantics, which is the first prerequisite for reaching a good specification. Section 4
emphasizes the fact that we need to consider several modeling solutions to a problem and choose
the most advantageous one with respect to the aspects under consideration. Section 5 shows the
role of OCL in specifying the various model uses, while Section 6 justifies through an example
the need of using snapshots for validating specifications. The paper ends with conclusions.
2
Teaching OCL Through Examples Integrated in Models
The teaching of OCL can be achieved in various ways. The classical approach emphasizes the
main language features: its declarative nature and first order logic roots, the type system, the
management of undefined values, the collection types together with their operations and syntax
specificities, and so on [CD10], [por]. Many examples used for collections employ expressions
with literals, which are context-independent and easy to understand.
OCL is a textual language which complements MOF-based modeling languages. The students’ interest in understanding and using the language increases if there are convinced with
respect to the advantages earned from enriching models with OCL specifications. To convince
students on the usefulness of using OCL, the chosen examples should be suggestive in terms
of models and enlightening in terms of earned benefits. That is why we have considered more
appropriate taking an “inverted curriculum”-type of approach, by introducing OCL through examples in which the specifications are naturally included in the models. Unfortunately, along
with positive OCL specification examples, the existing literature also offers plenty of negative
ones, starting with the WFRs (well-formedness rules) that define the static semantics of modeling
languages. The negative examples may wrongly influence students’ perception. Therefore, we
argue that a major issue in teaching OCL to students is explaining them the basic principles that
should be obeyed when designing OCL specifications, principles that should help them avoid
potential pitfalls.
An example that has been probably meant to argue for the use and usefulness of OCL (taking
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into account the title of the paper in question) is the one enclosed by the reference [Tod11]. The
examples and solutions proposed by this article provide an excellent framework for highlighting
important aspects that should be taken into account within the modeling process. In the second
semester of the 2010-2011 academic year, we have used these examples in order to warn students
Produce
byspecifications.
using OCL constraints
on the pitfalls that should be
avoidedmore
whenaccurate
enrichingdomain
models models
with OCL
3
Understanding the Model’s Semantics
A model is an abstract description of a problem from a particular viewpoint, given by its intended usage. The design model represents one of the possible solutions to the requirements of
the problem to solve. It is therefore essential for the students to realize the necessity of choosing a
suitable solution with respect to the aspects under consideration. The first prerequisite for designing such a model is a full understanding of the problem at hand, reflected in a thorough informal
Produce more accurate domain models by using OCL co
requirements specification. Nygaard’s statement “Programming is Understanding” [Ven04] is to
be understood as “Modeling
Understanding”,
since “Object-oriented
Anais
Todorova
(ana.todorova@orange-ftgroup.com),
Researchdevelopment
and Developmentpromotes
Engineer, France Télécom-Orange
the view that programming is modeling” [Nie11]. Understanding is generally acquired through
Summary: To build more precise models that are as close as possible to the reality of the relevant business, we often ne
an iterative and incremental
in which
OCL
specifications
playexplains
a major
role. That
howprocess,
to build useful
and accurate
domain
models, this article
the validation
processisof a domain model written i
Rational®something,
Software Architect
using
the EMF
validation
framework.
because, “if you don’t understand
you and
can’t
code
it, and
you gain
understading trying
to code it.” [Ven04].
Date: 15 Mar 2011
Advanced mentioned in the previous section, describes parentsThe modeling example Level:
from [Tod11],
PDF: A4 and Letter (679KB | 17 pages)Get Adobe® Reader®
children relationships in a community of persons. However, the model requirements description
is incomplete with respectActivity:
to both4821
itsviews
intended functionalities and its contained information.
Comments: 0 (View | Add comment - Sign in)
In such cases, the model specification, both
the graphical and the complementary textual one
Average rating (5 votes)
(through Additional Operations
AOs, invariants, pre and post-conditions), should contribute
Rate this-article
to enriching the requirements description. The process is iterative and incremental, marked by
Software modeling has traditionally been a synonym for producing diagrams. Most models consist of several squares and
repeated discussions among
clients
andadevelopers,
until tothe
convergence
of imprecise
views from
both inconsistent. Therefore
conveyed
by such
model has a tendency
be incomplete,
informal,
and, sometimes,
modeling
is
the
creation
of
models
that
are
accurate
and
conform
to
reality.
parties.
The proposed solution should
allowof aancorrect
management
of information related to persons,
Requirements
accurate domain
model
even when this information is incomplete. Unknown ancestors of a particular person is such a
Let's consider a genealogical tree as an example, starting with the diagram in Figure 1. The UML model of the genealog
case (sometimes not even the
natural
parents
known).
Forhave
such
cases,
the
provided
in it shows that one Person
defined
by name
and sex are
and can
have or not
children,
who
aremodel
also Persons.
Furthermore,
Persons.
means that the two
have the same
sex, butinduced
that is genetically
[Tod11] and reproduced inalso
Figure
1 This
is inadequate,
dueparents
to thecaninfinite
recursion
by theimpossible. Therefore, this m
self-association requiring each person to have valid references towards both parents. Snapshots
1. Genealogical
tree modelmissing will be thus qualified as invalid.
containing persons with at Figure
least one
parent reference
Figure 1: Genealogical tree model [Tod11]
Both this problem and
A UML diagram, such as a class diagram, is generally not precise enough to provide all relevant elements of a business m
constraints through multiplicities, but other constraints often remain implicit. If we need to describe additional constrain
often
described in
a natural language.
This practice
has always shown
that it leads to
its
solution,
consisting
in relaxing
the parents
multiplicity
toambiguities.
0..2,
Formal languages have been developed to avoid these ambiguities. The disadvantage of the traditional formal languages
who possess a solid mathematical knowledge, but they are difficult to use for a modeling system. OCL (Object Constrain
fill this gap. It's a formal language that remains easy to read and write. The expressions written in OCL can be interprete
in different roles, such as an analyst and a developer, for example.
7th EduSymp 2011
To create a precise and complete model, we need both UML diagrams and OCL expressions. Without the OCL expressio
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underspecified. The UML diagrams
remain indispensable for the representation
of classes and associations, but the OCL
nonexistent model elements, because there is no way in OCL to specify classes and associations. It's only when we comb
constraints that we can completely specify the model.
are now “classical” [Cab11]. Partial or total lack of references (1 or 0 multiplicity) indicates that
either one or both parents are unknown at that time.
The only constraint imposed in [Tod11] on the above mentioned model requires the parents of
a person to be of different sexes. Following, there is its OCL specification, as given in [Tod11].
self.parents->asSequence()->at(1).sex <> self.parents->asSequence()->at(2).sex
Although apparently correct, this expression encloses a few pitfalls:
1. In case there are valid references to both parents, but the sex of one of them is not specified,
the value of the corresponding subexpression is undefined and the whole expression reduces to either undefined <> Sex::Male or undefined <> Sex::Female.
This later expressions provide tool-dependent evaluation results (true in case of USE
[use] and undefined in case of OCLE [LCI]). The results produced by OCLE comply
with the latest OCL 2.3 specification [OMG11]. However, as the topic of evaluating undefined values has not yet reached a common agreement, students should be warned on
this.
2. In case at least one parent reference is missing and the multiplicity is 2, the evaluation
of WFRs should signal the lack of conformance among the multiplicity of links between
instances and the multiplicity of their corresponding association. To be meaningful, the
evaluation of model-level constraints should only be performed in case the model satisfies
all WFRs. Unfortunately, such model compilability checks are not current practice. In
case the parents multiplicity is 0..2, the model will comply with the WFRs, but the
constraint evaluation will end up in an exception when trying to access the missing item
(due to the at(2) call);
3. The OCL expression would have been simpler (not needing the asSequence() call), in
case an ordering relation on parents had been imposed at the model level.
Ordering the parents collection with respect to sex (such that the first element points to the
mother and the second to the father) allows writing a more detailed invariant shape. Following,
there is the OCL specification we propose in this respect, in case both parents are known. In
case of invariant violation, the debugging information is precise, allowing to easily eliminate the
error’s cause.
context Person
inv parentsSex:
self.parents->size = 2 implies
self.parents->first.sex = Sex::female and self.parents->last.sex = Sex::male
Yet, a correct understanding of the model in question leads to the conclusion that the mere
constraint regarding the parents’ sex is insufficient, despite its explicit specification for each
parent. As rightly noticed in [Cab11], a person cannot be its own child. A corresponding OCL
constraint should be therefore explicitly specified.
context Person
inv notSelfParent:
self.parents->select(p | p = self)->isEmpty
However, restricting the age difference among parents and children to be at least the minimum
age starting from which human reproduction is possible (we have considered the age of sixteen)
leads to a stronger and finer constraint than the previous, that may be stated as follows:
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context Person
inv parentsAge:
self.parents->reject(p | p.age - self.age >= 16)->isEmpty
In the above expression, each Person is assumed to own an age attribute. The reject
subexpression evaluates to the collection of parents breaking the constraint in question.
The fulfillment of this constraint could be also required at any point in the construction of the
genealogical tree. Assuming any parent to be created prior to any of its children, this restriction
could be stated by means of the precondition included in the contract below.
context Person::addChildren(p:Person)
pre childrenAge:
self.children->excludes(p) and self.age - p.age >= 16
post chidrenAge:
self.children->includes(p)
The conclusion that emerges so far is that the lack of OCL specifications prohibiting undesired
model instances (such as parents having the same sex, self-parentship or the lack of a minimum
age difference among parents and children) seriously compromises model’s integrity. The first
prerequisite for models to reach their purpose is to have a complete and correct specification of
the requirements, and to deeply understand them. An incomplete specification reveals its limits
when trying to answer questions on various situations that may arise. Specifying and evaluating
OCL constraints should enable us to identify and eliminate bugs, by correcting the requirements
and the OCL specifications themselves. Another conclusion, as important, is that the model
proposed in the analyzed paper does not fully meet the needs of such a problem, and we are
therefore invited to seek for a better solution.
4
Modeling Alternatives
A model equivalent to that of Figure 1, but which is more adequate to the specification of the required constraints, is the one included in Figure 2. The model in question contains two recursive
+mother
+father
0..1
NPerson
+mChildren
sex : Sex
age : Integer
0..n
name : String
+fChildren
0..1
0..n
Figure 2: An alternative model for expressing parents-children relationships
+employee and mChildren[ ]
associations: one named MotherChildren, with+user
roles mother[0..1]
*
User
0..n
and the other named FatherChildren, with roles
father[0..1]
and
fChildren[
].
*
0..1
Within this model, the constraint regarding the parent’ sex can be stated as proposed below.
+employer
+userContract
Library
+library
1
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+contract
0..1
0..n
LibraryContract
+companyContract +company
1..n
0..n
11
Figura x ‐ Library model explicitat Company
0..1
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Intrucat un rol principal constrangerilor este sa nu lase posibilitatea unor interpretari multiple, procesul context NPerson
inv parentsSex:
self.mother->size = 1 implies self.mother.sex = Sex::female and
self.father->size = 1 implies self.father.sex = Sex::male
Compared to its equivalent constraint stated for the model in Figure 1, the above one is wider,
since it also considers the case with a single parent and checks the sex constraint corresponding
to the parent in question. The problem with the previous model (the one in Figure 1) is that
we cannot count on an ordering when there is a single parent reference available. The parent
in question would always be on the first position, irrespective of its sex. As opposed to this, in
Figure 2, the parents’ roles are explicitely specified, with no extra memory required.
With respect to the second constraint, we propose the following specification in context of the
model from Figure 2.
context NPerson
inv parentsAge:
self.mChildren->reject(p | p.age - self.age >= 16)->isEmpty and
self.fChildren->reject(p | p.age - self.age >= 16)->isEmpty
The corresponding pre and post-conditions are similar to their equivalents from the previous
section, therefore their specification could be left to students, as homework.
5
Explaining the Intended Model Uses
Any requirements specification should include a detailed description of the intended model uses.
In case of the model under consideration, it is important to know what kind of information may
be required from it. Is it merely the list of parents and that of all ancestors? Do we want the
list of ancestors ordered, with each element containing parents-related information, in case such
information is available? Do we only need information regarding the male descendents of a
person?
In case of the initial model in which the recursive association is ordered, the list of all ancestors
of a person can be easily computed as follows.
context Person
def allAncestors():Sequence(Person) =
self.parents->union(self.parents.allAncestors())
The evaluation result for the constraint above is correct only if we assume the genealogical
tree as loops-free. This latter constraint is implied by the one restricting the minimum age difference between parents and children. In the absence of this assumption, the OCL expression’s
complexity increases.
A simpler alternative for this case employs the semantic closure operation on collections. This
operation, now included in OCL 2.3, has been implemented in OCLE ever since its first release
and returns a set.
context Person
def allAncestors():Sequence(Person) =
(Sequence{self}->closure(p | p.parents))->asSequence
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The asSequence() operation orders the collection it is applied on with respect to the insertion time of each element. In OCLE, elements appear in the same order they were added to
the set.
In case of the model from Figure 2, the use of the Tuple data type allows us to design a specification enclosing more suggestive information. Following, there is the proposed specification.
context Nperson
def parents:TupleType(mother:Nperson, father:NPerson) =
Tuple{mother = self.mother, father = self.father}
def allAncestors:Sequence(TupleType(mother:Nperson, father:NPerson))=
Sequence{self.parents}->closure(i |
i.mother.parents, i.father.parents))->asSequence->prepend(self.parents)
6
Using snapshots to better understand and improve the requirements and the model
One of the primary roles of constraints is to avoid different interpretations of the same model.
Therefore, the specification process must be seen as an invitation for a complete and rigorous
description of the problem, including the constraints that are part of the model. The model
must conform to the informally described requirements, even before attaching constraints. In
case this condition is not fulfilled, the constraints specification process must ask for additional
information, meant to support an improved description of requirements, a deeper understanding
of the problem, and by consequence, a clear model specification.
Despite its importance, as far as we know, this issue has not been approached in the literature.
That is why, in the following, we will try to analyze the second example presented in [Tod11],
concerning a library model. This example aims to model the contractual relationships between
a library, its users and companies associated with the library. The only informal specification
provided is the following: “In this example, we’ll assume that the library offers a subscription
to each person employed in an associated company. In this case, the employee does not have
a contract with the library but with the society he works for, instead. So we add the following
constraint (also shown in Figure 10): . . .”.
First of all, we would like to remind the definition of a contract, as taken from [glo]: “A
binding agreement between two or more parties for performing, or refraining from performing,
some specified act(s) in exchange for lawful consideration.” According to this definition and to
the informal description of requirements, we conclude that, in our case, the parts in the contract
are: the user on the one hand, and the library or the company, on the other hand. Therefore,
the natural context for the constraint is Contract. As one of the involved parts is always the
user, the other part is either the library (in case the user is not employed in any of the library’s
associated companies), or the company (in case the user is an employee of the company in
question).
Regarding the conformance among requirements, on the one side, and model, on the other side
(the class diagram, the invariant presented in Figure 10 and the snapshots given in Figures 12 and
13), several questions arise. Since a thorough analysis is not allowed by the space constraints
of this paper, in the following, we will only approach the major aspects related to the probable
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usage of the model. In our opinion, this concerns the information system of a library, that stores
information about libray users, associated companies, books, book copies and loans. The library
may have many users and different associated companies.
Since the Library concept is missing from the model, we have no guaranty that, in case
the user is unemployed, the second participant to the contract is the library. Moreover, in case
the user is employed, the invariant proposed in [Tod11] does not ensure that both the user and
the corresponding company are the participants to the contract. In our vision, two invariants are
needed - one in the context of Contract and the other in the context of User.
Figure 3: A revised version of an excerpt of the library model from [Tod11]
context Contract
inv onlyOneSecondParticipant:
self.library->isEmpty xor self.company->isEmpty
context User
inv theContractIsWithTheEmployer:
if self.employer->isEmpty
then self.contract.library->notEmpty
else self.employer = self.contract.company
endif
The above constraints forbid situations like those from Figure 4 (in which the user u1 has
a contract c1 both with the library l1 and the company comp1) and Figure 5 (in which the
user is employed by comp3, but its contract c2 is with comp2). This undesirable model
Figure 4: The user has a contract with both the library and the company
instantiations are not ruled out by the invariant proposed in [Tod11] in the User context, namely
self.contract->notEmpty xor self.company <> null.
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Figure 5: The user is employed by comp3, but its contract c2 is with comp2
Even more, in Figure 12 from [Tod11], contractB65 and contractR43 have only one
participant, company80Y, a stange situation in our oppinion. Also, in the same figure, if
userT6D is unemployed by company80Y, and, by consequence, contractQVR is between
userT6D and the library, we cannot understand why company80Y (which does not include
among its employees userT6D) has a reference towards contractQVR between userT6D
and the library.
Unfortunately, as stated before, our questions do not stop here. In Figure 10 from [Tod11], a
user may have many contracts, but in the requirements a different situation is mentioned. In the
class diagram of Figure 10, all role names are implicit, which burdens the inteligibility of the
model.
In this example, the snapshots meant to be used for testing have supported us in understanding
that the requirements are incomplete and, by consequence, so are the model and the proposed
invariant. In such cases, improving the requirements is mandatory.
7
Conclusions
The building of rigorous models, which are consistent with the problem requirements and have
predictable behavior, relies on the use of constraints. Such constraints are not independent, they
refer to the model in question. Consequently, the model’s accuracy (in terms of the concepts
used, their inter-relationships, as well as conformance to the problem requirements) is a mandatory precondition for the specification of correct and effective constraints. In turn, a full understanding of the model’s semantics and usage requires a complete and unambiguous requirements
specification. Requirements’ validation is therefore mandatory for the specification of useful
constraints.
The examples presented in this article illustrate a number of bugs caused by failure to fulfill
the above-mentioned requirements. Unfortunately, the literature contains many erroneous OCL
specifications, including those concerning the UML static semantics, in all its available releases.
Having free access to public resources offered via the web, students should know how to identify
and correct errors such as those presented in this article. Our conclusion is that the common
denominator for all the analyzed errors is hastiness: hastiness in specifying requirements, hastiness in designing the model (OCL specifications included), hastiness in building and interpreting
snapshots (test data).
There are, undoubtedly, several ways of teaching OCL. The most popular (which we have
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referred as the “classic” one, due to its early use in teaching programming languages), focuses on
introducing the language features. OCL being a complementary language, we deemed important
to emphasize from the start the gain that can be achieved in terms of model accuracy by an
inverted curriculum approach. In this context, we have insisted on the need of a complete and
accurate requirements specification, on various possible design approaches for the same problem,
as well as on the necessity of testing all specifications by means of snapshots.
However, the teaching and using of OCL has a number of other very important issues that
have not been addressed in this article, such as the specifications’ intelligibility, their support for
model testing and debugging, code and test data generation, language features, etc. The theme
approached by this article only concerns, in our view, a first introduction to the language and its
purpose.
Acknowledgements: This work was supported by CNCSIS-UEFISCSU, project number PNIIIDEI 2049/2008.
Bibliography
[Cab11]
J. Cabot. Common UML errors (I): Infinite recursive associations. 2011. http://
modeling-languages.com/common-uml-errors-i-infinite-recursive-associations/.
[CD10]
J. Chimiak-Opoka, B. Demuth. Teaching OCL Standard Library: First Part of an
OCL 2.x Course. ECEASST 34, 2010.
[glo]
InvestorWords. http://www.investorwords.com/1079/contract.html.
[LCI]
LCI (Laboratorul de Cercetare ı̂n Informatică). Object Constraint Language Environment (OCLE). http://lci.cs.ubbcluj.ro/ocle/.
[Nie11]
O. Nierstrasz. Synchronizing Models and Code. 2011. Invited Talk at TOOLS 2011
Federated Conference, http://toolseurope2011.lcc.uma.es/#speakers.
[OMG11] OMG (Object Management Group). Object Constraint Language (OCL), Version 2.3
Beta 2. 2011. http://www.omg.org/spec/OCL/2.3/Beta2/PDF.
[por]
The
OCL
portal.
http://st.inf.tu-dresden.de/ocl/index.php?option=com
content&view=category&id=5&Itemid=30.
[Tod11]
A. Todorova. Produce more accurate domain models by using OCL
constraints.
2011.
https://www.ibm.com/developerworks/rational/library/
accurate-domain-models-using-ocl-constraints-rational-software-architect/.
[use]
A UML-based Specification Environment. http://www.db.informatik.uni-bremen.de/
projects/USE.
[Ven04]
B. Venners. Abstraction and Efficiency. A Conversation with Bjarne Stroustrup - Part
III. 2004. http://www.artima.com/intv/abstreffi2.html.
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Teaching MDE through the Formal Verification of Process Models
Benoit Combemale2 , Xavier Crégut1 , Arnaud Dieumegard1 , Marc Pantel1 and
Faiez Zalila1
1
Firstname.Lastname@enseeiht.fr
Université de Toulouse, IRIT – France
2
Firstname.Lastname@irisa.fr
Université de Rennes 1, IRISA – France
Abstract: Model Driven Engineering (MDE) plays now a key role in the development of Safety Critical Systems (SCS) relying on Domain Specific Modeling
Languages (DSML), early Validation and Verification (V&V) and Automatic Code
Generation. It reduces the development cost and improves the system qualities. This
contribution describes the content and provides the lessons learned from a course
about MDE for SCS development that started five years ago. This course focuses
on the use of DSML to allow early V&V based on formal methods. It relies on a
process modeling and verification case study that leads students to experiment the
various MDE tools that ease the definition and implementation of Domain Specific
CASE tool. MDE is introduced as a bridge between the formal methods course
that introduces specific formalisms (e.g., Petri net) dedicated to efficient verification
tools (e.g., model-checker), and the software modeling course that promotes user
oriented abstraction through DSML. The unification power of MDE is also highlighted by the case study that does not target traditional executable software.
Keywords: Modeling language engineering, Formal verification, Metamodeling,
Concrete syntax specification, M2M and M2T Model transformations
1
Introduction
The Model Driven Engineering (MDE) course presented in this contribution was designed in
2007 for M2 students in System and Software Engineering in Toulouse where Aeronautics, Automotive and Space transportations, and especially the development of safety critical systems,
are the key industries. Nowadays, in these domains, model based early verification and validation activities conducted by engineers is a common practice. It is also widely acknowledged
that testing does not allow to reach the required level of safety at affordable costs and that MDE
techniques allow to raise the quality of the developed system while opening doors toward formal verification. This course gathers these elements to prepare the students to enter efficiently
the system engineering world. Most of the time, when a verification is done in MDE, it relies on OCL constraints (as in [BKSW09],[GP10]). This course relies on model-checking for
Petri nets in the context of MDE to verify behavioral correctness that are hardly verified with
static verification solutions like OCL. The necessity for earlier verifications is highlighted by
the non-executable software targeted in this course: a simple process modeling language. This
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<< enumeration >>
WorkSequenceType
Process
name: EString[1]
1..*
activities
WorkDefinition
0..*
workSequences
predecessor
1
name: EString[1]
successor
1
linksToSuccessors
0..*
startToStart
finishToStart
startToFinish
finishToFinish
WorkSequence
linksToPredecessors linkType: WorkSequenceType[1]
a
startToStart
finishToStart
b
c
finishToFinish
0..*
Figure 1: First metamodel of SimplePDL (left) and one conforming model (right)
allows us to explain how software modeling and formal verification can coexist during a system
development and gives a practical overview of technologies easing the introduction of formal
verification technologies such as model-checking1 . The key principle was to apply the various
technologies allowing to implement a Domain Specific CASE tool such as TOPCASED2 to a
verification driven case study. This case study has also been used to illustrate the TOPCASED
approach to system engineering.
This contribution is structured as follows. Section 2 presents the simple process modeling
language use case that structures the whole course. Section 3 lists the main topics addressed
by the course and further described in the next sections: metamodeling and static semantics
constraints (section 4), concrete syntaxes (section 5) and transformations (section 6). Section 7
presents some extensions to the initial use case that allows student to develop and validate the
acquired knowledge. Finally, section 8 explains how the course is conducted in the different
contexts and gives some insights on future evolutions.
2
Formal Verification of Processes: SimplePDL to Tina Case Study
The main target of this course is the development of safety critical systems using Domain Specific Modeling Languages (DSML) and formal verification technologies. A simple yet realistic
concrete case study is used all over the course in order to illustrate the different concepts and
associated tools of MDE that are used to create DSMLs and to connect them to existing tools.
The starting point is a very simple SPEM-based process modeling language called SimplePDL
and the termination verification activities.
The S IMPLE PDL metamodel (Figure 1) defines the process concept (Process) composed of a
set of activities (WorkDefinition) representing the activities to be performed during the development. The concept of WorkSequence illustrates temporal dependencies between work definitions:
the target activity can only be started or finished if the source activity is already started or finished. The kind of constraint (linkType) is expressed using the enumeration WorkSequenceType.
For example, the c activity (right of figure 1) can only be started when a is finished and finished
when b is finished. This first metamodel is obviously oversimplified but some extensions are
proposed in section 7 to gain in expressiveness and validate the acquired knowledge.
The end user purpose is to check properties on a SimplePDL model. For example, he may
asks whether the modeled process can finish (all activities from the process have been finished
1
2
The authors wish to thank F. Vernadat that gives that part of the course and initiated the whole activity.
http://www.topcased.org
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xSPEM
.ecore
ATL
PetriNet
.ecore
(M2M)
<<conformsTo>>
SimplePDL
2PetriNet
.atl
myProcess
.xspem
ATL
(M2T)
<<conformsTo>>
myProcess
.PetriNet
PetriNet
2Tna
.atl
myProcess
.net
Tina
properties
.ltl
Figure 2: Approach to evaluate behavioral properties on a process model
while respecting the sequencing constraints expressed by the work sequences).
To answer those questions, the students must reuse model-checking tools that they have studied in previous courses. We rely currently on the Tina toolkit3 for the verification activities using
Temporal Petri nets as modeling language and SE-LTL (State Event Linear Temporal Logic) as
property language. The principle of the verification is thus to translate a process model into a
behaviourally equivalent Petri net and then to express the common end users questions as LTL
formulae that will be checked by the Tina model-checker. A PetriNet metamodel is used to
avoid to be directly wired to the Tina input syntax. Thus, as depicted in Figure 2, the overall
approach is composed of a model to model (M2M) transformation (SimplePDL to PetriNet) and
two model to text (M2T) transformations (PetriNet model to Tina concrete syntax for the first
one and SimplePDL model to LTL concrete syntax for the second).
3
Content and Schedule of the Course
The course presents the main concepts and tools of MDE as a set of 7 topics4 grouped into 3
themes (metamodeling, concrete syntaxes and model transformations) and ends with a project as
listed in the following table and developed in the next sections.
Metamodeling
(section 4)
Concrete Syntaxes
(section 5)
Model transformations
(section 6)
Project (section 7)
1. Metamodeling using Eclipse/EMF
2. Static semantics using OCL
3. Textual concrete syntaxes using Xtext
4. Graphical concrete syntaxes using GMF generators
5. Model to Model transformation using ATL
6. Model to Text transformation using xPand
7. Model to Text transformation using ATL
Implementing extensions to the case study
One lecture (≈2h) and a practical work session (≈2h) is allocated to each topic. Lectures
present the main concepts and associated standards. For each topic5 , except the two last one, the
3
http://www.laas.fr/tina/
An optional topic called “The Tina toolkit” is a 20 minutes tutorial that explains to students who have never used the
Tina toolkit how to perform model-checking. It is not described here as it is not strictly related to MDE technologies.
5 Teaching materials are available at http://cregut.perso.enseeiht.fr/2010/ but, unfortunately, currently only in French.
4
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practical session has the same three-part structure. The first part is a tutorial that presents the
concepts and tools illustrated on the SimplePDL language. The second part provides exercises
to ensure that the students got a good understanding. Exercises consists in completing the work
done in the first part. The third part is an open exercise that asks the student to do a similar work
on the Petri net language, without any guidance. The first two parts are usually finished in about
two hours of supervised work but the last one is often only started in the supervised time slot and
students have to finish it on their own.
Finally, a project is done by students: the implementation of several extensions to the main
case study. Section 7 describes the extensions. First, a 6 hours assignment is used to assess that
students master the MDE concepts and tools. It is based on the E1 and E2 extensions of section 7.
An oral presentation and demonstration is organized. Then, the other extensions are implemented
by the students (18 hours of personal work). These extensions can be done independently in order
to avoid unnecessary difficulties in regard to the evaluation of their understanding. Students pass
an oral examination where they show the result of their work and explain how they conducted
this work, what were their main choices and why they made them.
All tools used in practical work are based on the open-source Eclipse platform and are part
of (or can be added in) the Eclipse Modeling Tools6 . This choice allows students to go on with
their work using any computer, and have a unified environment for all the tasks they have to do.
4
Metamodeling
The first topic focuses on metamodeling using the Ecore language from the Eclipse Modeling
Framework7 . Students use the Ecore graphical editor to load the initial metamodel of SimplePDL
(Figure 1). They use EMF to generate Java classes to load and store models, and a structured
editor that is then used to edit small process models. The structured editor provides a good
understanding of the containment attribute of an EReference (and a concrete example of the
composition relationship already seen in UML classes that took place in the previous years).
Furthermore, the eOpposite attribute also helps in the understanding of the UML association
(when one reference is updated, the opposite reference is also updated).
The second part of this topic consists in modifying the metamodel by adding a ProcessElement
metaclass to generalize WorkDefinition and WorkSequence elements and a Guidance element
that allows to associate a natural language description to any process element. Aside manipulating the Ecore editor, students discusses advantages and drawbacks of their metamodels.
Finally, students have to define a metamodel for Petri nets from scratch. The starting point is
a textual description of Petri nets (taken from wikipedia) with some model examples. Examples
are easier to understand by the students but they lead them to define a partial metamodel that has
to be completed using the information provided in the textual description. It is a very interesting
exercise because several metamodels are usually provided by the various students and many
exchanges take place in order to define the best one according to various criteria.
Furthermore, the Petri net metamodel does not capture all the constraints of Petri net models.
It thus demonstrates the need to define the static semantics. We use OCL for that purpose.
6
7
cf. http://www.eclipse.org/downloads/packages/eclipse-modeling-tools/indigor
See the Eclipse Modeling Project: http://www.eclipse.org/modeling
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process dvp {
wd a
wd b
wd c
ws s2s from a to b
ws f2f from b to c
ws f2s from a to c
}
process dvp {
wd a
wd b starts if a started
wd c finishes if b finished
starts if a started
}
Figure 3: Two possible textual concrete syntaxes for SimplePDL
OCL and static semantics is presented in the next topic. The TOPCASED OCL checker is used
for practical activities. When an invariant does not hold, the context element is red marked. First,
students must write some OCL constraints in order to understand the basics of this language. The
use of the tools allows to stress that it is important to define an invariant at the right place. For
example, expressing that activity names are unique may be expressed as an invariant on Process
but marking a Process element as wrong is of little help to find the bad activities. Thus, this
invariant is better expressed on WorkDefinition elements so that bad activities are highlighted.
Thanks to the Petri net metamodel, students can notice that there is a balance to be found
between having a simpler metamodel with less concepts and relationships but more OCL constraints, or a more complex metamodel with less OCL constraints.
5
Concrete syntax
A metamodel only describes an abstract syntax. Models are stored as XML or XMI files that
could be considered as concrete syntaxes but these are not designed as editing tools for the end
user. Thus, it is mandatory to provide concrete syntaxes, like the Ecore diagram defines a graphical concrete syntax for Ecore models. In this course, textual concrete syntaxes are presented
using Xtext and graphical ones using GMF Tooling.
5.1
Textual Concrete Syntaxes
Xtext8 is used as a tool to define concrete syntaxes. Figure 3 proposes two examples of concrete
syntaxes for the S IMPLE PDL model presented on the right of figure 1. The first one is used to
explain the concepts of Xtext: both the concrete syntax and the Xtext files are provided. Then,
the Xtext file corresponding to the second syntax is given and students have to find the concrete
syntax it corresponds to. They first have to write it on a paper to ensure they understood the
grammar as defined in Xtext, then they can test it using the generated Eclipse editor. Finally,
they have to define their own textual concrete syntax for Petri nets.
Xtext can generate the metamodel that is closely related to the structure of the grammar provided in Xtext for the concrete syntax. The metamodel corresponding to the first syntax is close
to the one of Figure 1 whereas the second one is very different. Students are thus shown that a
compromise must be found between the structure of the grammar and the structure of the generated metamodel. Using an existing metamodel is also possible but is a bit tricky.
The main lesson is that the “natural” metamodel defined for a domain is generally not wellsuited for defining the concrete syntax. It is thus better to let Xtext generate its own metamodel
8
http://www.eclipse.org/Xtext
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and then use a M2M transformation to translate this one into the other. Xtext allows to automatically use an Xtend transformation in that purpose but we do not teach that feature to students.
5.2
Graphical Concrete Syntaxes
Graphical concrete syntaxes allows to built a graphical editor for a given metamodel. It is very
attractive for the students to be able to do so in a very short time.
From a pedagogical point of view, graphical editors are a good illustration of MDE principles,
and generative approaches. The user only has to describe in a declarative manner the features of
the expected editors, and the different generators get the things done. Moreover, while most of
the generative approaches are defined for a given DSML to automate tasks from the conforming
models, the use of such generative approaches can highlight the usefulness of a metametamodel.
We initially used the simple graphical editor generator provided by TOPCASED. All aspects
required to describe the editor were blurred in the same configuration model (the Views, the
Controler and their mapping to the Model in the MVC pattern) and it provided only few possible
customizations.
For three years now, we have switched to GMF Tooling9 that is part of the Eclipse Modeling
bundle. GMF Tooling puts a better stress on separation of concerns as it is based on different
models that describe each parts of a graphical editor: tools, graphical representation of elements,
palette and mappings among these models and the Ecore metamodel. It also uses OCL to define
some behavior, for example to prevent a reflexive transition (illustrated on the WorkSequence
element). Unfortunately GMF tooling has suffered from nasty bugs for years that generate files
with obvious mistakes that have to be hand-corrected by students, which is very confusing.
The main drawback of these tools is that they are quite complex and, often students only
perform the required actions without reading the explanations and understanding the underlying
motivations. Thus, at first sight, students consider those tools as tedious. Furthermore, they lack
many features and does not help when they want to build their own editor for PetriNet models
without writing Java code. It is why we plan to switch to OBEO Designer10 to have a more
robust and sophisticated tool.
6
Model Transformation
The last topics concern model transformation. Model to model transformations (M2M) are presented using ATL. ATL and xPand are used for model to text transformations (M2T).
6.1
Model to Model Transformations
M2M transformations are a key concept of the MDE course. A presentation of QVT [OMG08]
specification puts the focus on the operational and declarative parts. Many languages are available. We could have used operational languages such as Kermeta, xTend, SmartQVT, EMP
Operational QVT, Epsilon Transformation Language, etc. But we feared that students would
9
http://wiki.eclipse.org/GMF
http://www.obeodesigner.com
10
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a
startToStart
finishToStart
b
a notStarted
b notStarted
a start
b start
c notStarted
c start
c
finishToFinish
a running a started b running b started c running c started
a finish
b finish
a finished
b finished
c finish
c finished
Figure 4: Translation of a process composed of work definitions a, b and c into a Petri net
only consider them as classical programming languages. Indeed, they have to manage explicitly
the control flow, track links to already created target elements, etc. Their major benefit over a
language like Java is their powerful query language and collections operators derived from OCL.
We have chosen ATL and we mainly use its declarative part so that students can concentrate
on how to map source elements to target elements. In practice, they write a rule for each source
element and describe the elements that have to be created in the target model.
Before handling technical details, we first ask students to find how to translate a SimplePDL
model into a Petri net in order to verify that the modeled process terminates. We take a very
simple process like the one on the left of figure 4. The corresponding Petri net is on the right of
this figure. The purpose is that they gain a good understanding of the mapping between process
models and Petri nets. Each WorkDefinition is translated into three places characterizing its state
(notStarted, running and finished) linked by two transitions. These transitions model the actions
that we want to observe on an activity: one can start an activity and then finish it. An activity
is considered as started if it is running or finished. This is recorded by the place called started.
A WorkSequence becomes a read-arc11 from one place of the source activity (either started or
finished) to a transition of the target activity (either start or finished) according to the kind of
WorkSequence. This allows to illustrate a property driven approach to formal model design.
To show the principles of ATL, we give the rule that translates a Process into a PetriNet and
the beginning of the rule that translates a WorkDefinition into nodes, places and arcs. Process to
PetriNet is a 1 to 1 rule. Students have to complete the WorkDefintion2PetriNet rule. This rule
creates 4 places, 2 transitions and 5 arcs for each work definition (1 to n rule). The only difficulty
is that a process element does not have direct access to its process container. An ATL helper is
provided to access the missing reference.
Finally, they add a new rule to translate one work sequence into a PetriNet read arc (1 to 1
rule). This last rule illustrates the use of resolveTemp ATL operator (resolveIn in QVT)
which allows to select one element of the target model among those built from a given source
model element (in a 1 to n rule).
Operational constructs or more advanced concepts like rule inheritance, called rules and so on
are mentioned but not used. One important aspect of the use case is that it allows this kind of
simple declarative transformation. It would be useful to illustrate also an example that is really ill
fitted and requires a more imperative transformation, however we lack time to have the students
do the experiment and can only give insights on this problem.
11
A read-arc checks that enough tokens are in the input place. Tokens are not withdrawn when the transition fires.
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6.2
Model to Text Transformations
A first example shows how xPand may be used to generate the graphical concrete syntax of
SimplePDL proposed in Fig. 4. Then, students have to generate a DOT file for textual graph
representation. The final exercise consists in generating the Tina text from a Petri net model.
Students are quite familiar with template languages due to the use of JSP in previous courses
and have no problem to use xPand despite its verbose syntax and the use of non common characters (even for french students).
ATL also provides M2T transformations as queries. We provide the students with the ATL
query that translate a Petri net model into Tina syntax. All aspects of Petri net are handled except
for time constraints. So, once students have noticed that ATL allows to define helpers on metamodel elements and uses a query language very close to OCL, they complete the query to handle
time constraints. They are then able to write from scratch the second M2T transformation that
generates the LTL formulae corresponding to the questions asked on the process (they obviously
depends on the process model). The main drawback of ATL is that mistakes are generally not
highlighted in the editor because they are only detected at runtime.
7
Case Study Extensions
The initial case study allows to introduce MDE concepts and tools and to check that students
got a basic understanding of the technologies. Several extensions are proposed to students that
they have to develop on their own in order to improve their practice. These extensions are
listed hereafter with a short description of their strong points. For each extension, students
have to extend the core course realizations: extend the SimplePDL metamodel, add new OCL
constraints, update concrete syntaxes, M2M transformation to handle extensions and, eventually
the generation of LTL formulae. This work is done in autonomy and is eventually assessed. The
stress is also put on how they can validate their work.
E1 : Resources. Every work definition requires a set of resources to be executed.
E1 is quite easy to implement. SimplePDL metamodel is completed with two new concepts
Resource and Allocation to describe how many occurrences of a resource are needed by an activity. OCL constraints specifies restrictions on the amount of allocated resources with respect to
the total amount of resources. Extending concrete syntaxes is easy. The M2M transformation is
extended with two rules. The first creates one place for each Resource, the number of token is the
amount of available resources. The second adds two arcs so that an activity takes the resources
when it starts and releases them when it finishes.
E2 : Time constrained. Are activities able to finish in a defined time interval?
The idea is to add an observer on the activities to record if they finish too early, in time or too
late. The observer allows to answer both the initial question and the new one: may the process
finish? May it finish while respecting time constraints?
E3 : Hierarchical work definitions. A work definition can be split into sub work definitions.
It is mainly a modeling problem. Students have to find how to model hierarchical activities. It
also allows to illustrate the composite design pattern. On the ATL side, rule inheritance is useful
to avoid code redundancy.
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E4 : Suspending a work definition. A work definition may be suspended and its resources
released. It can then be resumed if the required resources are available at that time.
This extension is not difficult if we consider that time is not stopped when an activity is suspended. The main interest is that the SimplePDL metamodel is unchanged. Only its semantics
(encoded by the translation from process models to Petri nets) changes as an activity may be
suspended that leads to new possible scenarios to ensure the process finishes. Only the M2M
transformation is concerned by this extension.
E5 : Different possible sets of resources. A work definition can work with different sets of
resources (alternative resources).
The difficulty is to find how to represent the ”or” between resource sets in Petri nets.
8
Discussions
Modularity of the course Even if the purpose of the course was to present most of the MDE
concepts and tools, it is very modular and parts of it can be dropped of. In an alternate version,
only one lecture presents the main MDE concepts, then each of the 7 topic (section 3) is done
using 2 hours sessions. The first part of each topic is used to explain the concepts and see how
tools work. Students are asked to finish topics on their own. Finally, students have a 6 hours
session to implement the two first extensions and have to write a short report. Another one is
taught in only 8 hours. It consists in an overview of MDE at the end of the M2 level. There is
only a 2 hours lecture to present the main concepts of MDE and 6 hours of practical sessions, 2
hours for metamodeling with SimplePDL and PetriNet (OCL is left as homework) and 4 hours
for model transformation (focusing on M2M transformation). Concrete syntaxes have already
been studied during M1.
Formal verification use case is not a difficulty. Even if the course is based on a verification
case study. We have experienced that the lack of knowledge in formal verification and modelchecking is not an issue. Petri net are indeed an easy to understand formalism and students
are able to define its metamodel and propose a translation of SimplePDL model into Petri net.
Furthermore, it allows to present model-checking to students and put the focus on the importance
of early verification in the development process.
Technical overload The practical work causes some troubles to students. In particular, when
making the metamodel evolve, students often do not entail the consequences of their choices and
need some help to validate their proposals. Furthermore, all the steps required to verify a model
are run manually: running the M2M transformation, running the two M2T transformations to
generate the Petri net file and the LTL formulae, running the Tina model-checker. Presenting
tools to automate these steps (like Ant or a workflow engine) could favor the adoption. We are
also surprised that students are not asking for such tools.
Studying verification does not imply the verification of the study We observed that students
are not really concerned about the validity of their development, despite the fact they had to
develop verification tools and thus are aware of that. A major problem is that students do not
rigorously verify their work (OCL constraints, transformation...). Students only use the example
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provided in the subject to validate their work whereas they should define many wrong models
to ensure that all inconsistencies are caught by the OCL invariants, define several models to test
the different aspects of their transformations, etc. In fact students are not really experienced at
defining good test cases that provide a significant coverage.
Students’ difficulties The students’ difficulties we have seen in this course are twofold: one is
the necessary ability to find the right level of abstraction, especially making the right choices in
the design of language is essential to reduce the accidental complexity generated each time the
metamodel changes. The other difficulty comes from the technical environment that may appear
complicated to learn, especially the lack of maturity and performance of certain tools, and the
proliferation of tools which continues to evolve. We noticed that students encounter in particular
one of these difficulties according to their curriculums. While some students are comfortable
with a complex technical environment but have difficulty with abstraction, other students easily
manipulate abstractions but are struggling to implement them using the MDE tools.
9
Conclusion and Perspectives
In this paper, we have presented how a case study may help in presenting MDE concepts and tools
in an attractive way that furthermore make students aware of formal verification technologies that
are getting more and more interest in the safety critical transportation systems industry. Despite
its verification focus that can be considered as difficult for most students, we have noticed that
it can also been taught to student with no formal background because Petri net are an easy to
understand language in its concepts and semantics.
For the future, we strongly believe that MDE course should be taught at M1 level because it
is becoming a very important domain, not only in academy but also in industry. Our main fear
about this is to know whether students will have enough background and experience on modeling
to be able to handle metamodeling and generative tools.
We also think that MDE is quite close to Software Language Engineering (abstract syntax,
concrete syntax, transformation of abstract syntax, etc) and thus it could be interesting to merge
these modules to gain on efficiency and stress the important points and favor separation of concerns: abstract syntax, concrete syntax, transformation. We now plan to rely on MDE technologies in our compiler course instead of classical attribute grammar technologies.
Bibliography
[BKSW09] P. Brosch, G. Kappel, M. Seidl, M. Wimmer. Teaching Model Engineering in the
Large. 2009. In: Educators’ Symposium @ Models 2009.
[GP10]
T. Gjosaeter, A. Prinz. Teaching Model Driven Language Handling. ECEASST,
2010. In: Educators’ Symposium @ Models 2010.
[OMG08]
Object Management Group, Inc. Meta Object Facility (MOF) 2.0 Query/View/Transformation (QVT) Specification, version 1.0. Apr. 2008.
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Mismatches between industry practice and teaching of model-driven
software development
Jon Whittle and John Hutchinson
School of Computing and Communications
Infolab21, Lancaster University, UK
Abstract: EAMDE was a 12 month research project, investigating how industry uses
model-driven software development (MDSD). Using quantitative and qualitative research
techniques, experiences were collected on the adoption and application of MDSD in 17
companies. The study highlighted examples of good and bad practice that lead to success
or failure with MDSD. Some of these practices appear to have ramifications on the way
that MDSD, and software modeling more generally, is taught within universities. This
paper presents three of the key findings relevant to education: (1) A significant number of
successful MDSD companies build their own modeling languages and generators,
suggesting a re-orientation of education away from UML notation to fundamental
modeling principles; (2) MDSD is generally taught top-down, whereas industry success is
more likely when MDSD is applied bottom-up; (3) successful application of MDSD
requires skills both in abstract modeling and compilers/optimization; however, these skills
tend to be separated in standard CS curricula.
Keywords: model-driven software development, education
1 Introduction
EAMDE1 was a twelve month empirical research project, beginning in October 2009, that
aimed to investigate how industry applies model-driven software development (MDSD) in
practice. The original motivation behind EAMDE was that, whilst there are some clear
benefits to MDSD (such as increased productivity through code generation), there are also
some potential drawbacks (such as increased training costs or difficulties in integrating legacy
code). The project aimed to discover what factors – technical, organizational and social – lead
some companies to succeed with MDSD, whereas others fail.
The methodology was to apply quantitative and qualitative research methods to understand
when, how and why companies do or do not succeed with MDSD. A three pronged approach
was followed: (i) a questionnaire widely disseminated to MDSD practitioners, which received
over 400 responses; (ii) in-depth interviews with 22 MDSD professionals from 17 different
companies; (iii) on-site studies observing MDSD in practice. In particular, the in-depth
interviews were recorded and transcribed, resulting in over 150,000 words describing rich and
detailed experiences of the application of MDSD spanning many years and covering a wide
range of MDSD knowledge (our interviewees had more than 360 years of software
engineering cumulative industrial experience).
The study was intended as an exploratory one, from which key themes would emerge to
suggest more formal research hypotheses. Results from the study have previously been
1
Empirical Assessment of the Efficacy of Model Driven Engineering, http://www.comp.lancs.ac.uk/~eamde
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described [1, 2]. In addition, however, some of the themes that emerged relate to the way that
MDSD, and software modeling more generally, is taught in universities.
This paper reports briefly on three key findings from the EAMDE study that suggest a
reconsideration of the way that modeling is taught. For each, we present the finding, illustrate
it using examples from our interviews, and suggest an alternative educational approach.
2 Greater Emphasis on Domain-Specific Modeling
A key observation from our study is that MDSD may be much more widespread than is
generally believed. We have found that some form of MDSD is practised widely, across a
diverse range of industries (including automotive, banking, printing, web applications etc.) and
in companies of varied size. The questionnaire respondents, for example, (all of whom were
MDSD practitioners) were employed in a range of different roles (37% developers, 36%
project managers) and represented a good spread of size of company with respect to the
number of people involved in software development (e.g. 53%<100 and 20%>1000).
Perhaps surprisingly, a significant number of MDSD examples from our study followed
domain-specific modeling paradigms. Around 46% of questionnaire respondents used in-house
or vendor-provided domain-specific modeling languages (DSLs). Interview data shows that a
very successful approach is to develop small DSLs for narrow, well-understood domains.
Practical application of domain modeling is pragmatic, where DSLs (and accompanying
generators) are developed sometimes in as little as two weeks. Hence, much MDSD success is
‘hidden’ – in the sense that there is very widespread use of mini-DSLs, often textual, and that
there may be many such mini-DSLs used within a single project: one interviewee reported on
the use of multiple XML-based DSLs to generate 70% of a system, for example.
This evidence of practice has ramifications on the way that modeling is taught. Most modeling
courses tend to focus on UML and, furthermore, emphasize the presentation of notation rather
than principles. This occurs perhaps because it is straightforward to teach notation – an OMG
standard exists that describes the notation explicitly and therefore offers a clear path to follow
both for textbook writers and educationalists. In contrast, there are relatively few books that
teach modeling principles. Our study suggests that, although UML may be an important
language to learn, it may be more beneficial to focus on underlying modeling skills. The
prevalence of DSLs points to the need for developers with skills in modeling that may be
divorced from any specific knowledge of UML notation.
Note that this does not necessarily mean a switch to focus on the notational details of a
particular metamodeling framework. Rather, we would advocate an emphasis on getting
students to understand the key concepts in a domain and using DSLs to show how such
concepts can be structured and organized. Most UML books put notation first and concept
structuring is either only secondary or hidden entirely. Although much more limited, books on
DSLs (e.g., [3]) seem to do a better job of teaching general principles of (domain) modeling.
The following quote from one of our interviewees is illustrative of the kind of difficulties that
a focus on notation can bring.
What we found is when we taught UML, we’d be teaching about classes and inheritance
relationships etc., and there’d be no practical use of this then you’d give an exercise and of
course it would be done badly… And what we basically realised is we were spending much
much more time discussing the semantics of the language…so we scrapped the course
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completely… we went out, we bought 4 boxes of the monopoly board game… We gave them
this, we said go model the game using these concepts…. We reintroduced the core of UML,
class diagrams, in about an hour and then we had people get on with it. We set this up so
they would spend 7/8 hours – a whole day – just modelling, playing with the concepts, so
they could write down things and then actually work with the sort of physical version of this
actually using the monopoly pieces, and actually exploring the concepts within this simple
board game – it’s quite a challenging board game
3 Teach MDSD Bottom-up rather than Top-down
Following on from the previous section, our findings lead us to believe that successful MDSD
practice tends to be driven from the ground-up. MDSD efforts that are imposed from highlevel management typically struggle. As a result, there are fewer examples of the use of
MDSD to generate whole systems. Rather than following heavyweight top-down
methodologies, successful MDSD practitioners use MDSD as and when it is appropriate and
combine it with other methods in a pragmatic fashion.
Those companies that do succeed invariably do so by driving MDSD adoption from the
bottom-up: that is, small teams of developers try out aspects of MDSD, which in turn leads
them to recognize reusable assets, and eventually MDSD propagates upwards to the
organisation as a whole. The following quote from our interviews is typical:
Yes, yes of course we started just with a few components and we started I think around [the
year] 2000 with the first component and now I think 50-60% of all our code is from re-used
building blocks but in the beginning it was only 5% or 10%
This way of working suggests that developers find it easier to get to grips with MDSD when
they use it to refactor existing assets from the ground-up rather than trying to abstract from
above. In turn, it suggests that modeling should be taught bottom-up rather than top-down.
A typical course in software modeling (and in software engineering, more generally) teaches in
a top-down fashion in which requirements models are first developed and are then iteratively
refined into architecture, design, code, etc. Students often have a great deal of difficulty
proceeding in this manner because it requires formulating abstractions of a system before the
concrete details are understood [4].
Given that success in industry seems to be associated with bottom-up introduction of MDSD,
we advocate an approach to teaching MDSD that mirrors this practice. Although as yet we
have no concrete proposals for such a course, one can imagine a programming-focused module
that starts with an existing system and asks students to develop slightly different versions of
some features of the system. This process could then be used to discuss the merits of defining
reusable assets and abstracting from those assets by defining a modeling language and code
generator. The advantage of such a course over most existing modeling courses would be that
abstraction skills are introduced and nurtured using very specific, concrete examples, which
give students a handle on the difficult topic of abstraction.
4 Integrate Abstraction and Compiler Skills within CS Curricula
As we have seen previously, successful MDSD companies often develop in-house domainspecific languages and code generators, or, in some cases, they extend or modify off-the-shelf
tools. In the interviews, we heard of two ways of achieving this task: either use separate
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developers, one for modeling and one for writing a generator that could produce optimized
code, or use a single developer capable of carrying out both developing a DSL and writing a
decent generator for it. The following quote is indicative of the former approach:
…they couldn't optimize the generated code so the way they had to do it was asking the
hardware guys to have more hard disc, more memory, because of the tool. So beforehand
we had very small memories and we'd been using C and we were very clear about the
memory map and each engineer has a clear view on how much memory space they can use.
But this case we cannot do something with the generated code so we simply ask the
hardware guys to have more hard disc.
The interviews tend to suggest that the second way of working is more successful. In other
words, companies that are successful with MDSD tend to have MDSD ‘gurus’ within the
organization who possess a combination of skills in both abstraction (modeling,
metamodeling, DSLs, etc.) and compiler/optimization. It is interesting to note, however, that
these two skill sets – abstraction/modeling and compiler/optimizations – tend to be quite far
apart in typical CS curricula. Although it may be common for a compiler course to be included
as a core module, taken by all CS students, software engineering is typically taught very
separately from this and usually does not make much reference to it, if any. The danger is that
students specializing in software engineering receive only very basic training in
compiler/optimization skills, which may cause problems when applying MDSD in practice, as
the following quote illustrates:
The tool itself is very inefficient. But I also developed a lot of CASE tools whilst I was at the
university as a PhD student, but if somebody asks me how to optimize your code from your
CASE tool, then I don't know how to do that!
Based on our study, we would argue that perhaps abstraction and compilation/optimization
techniques ought to be taught together in an integrated fashion. Although further study is
needed to validate this hypothesis, such an idea would radically alter the way that software
engineering is taught and would skill-up a new generation of developers capable of both
abstracting in a problem space and transitioning to a solution space in an efficient manner.
5 Conclusion
This paper has presented some insights from a large scale study on industry adoption of
MDSD, concentrating on those findings relevant to MDSD education. The paper has suggested
three ways to reconsider the way MDSD is taught, to better align with industry practice. At
this point, these suggestions are untested so further educational research is required to
investigate their potential benefits and understand their drawbacks.
6 References
[1] John Hutchinson, Jon Whittle, Mark Rouncefield, Steinar Kristoffersen: Empirical
assessment of MDE in industry. ICSE 2011: 471-480
[2] John Hutchinson, Mark Rouncefield, Jon Whittle: Model-driven engineering practices in
industry. ICSE 2011: 633-642
[3] Tony Clark, Paul Sammut, James Willans: Applied Metamodelling, A Foundation for
Language Development, 2nd Edition. Ceteva, 2008.
[4] Jeff Kramer: Is abstraction the key to computing? Commun. ACM 50(4): 36-42 (2007)
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Ready for the Industry: A Practical Approach to Teaching MDE
Gordana Milosavljević1 , Igor Dejanović2 and Branko Perišić3
1
grist@uns.ac.rs
igord@uns.ac.rs
3 perisic@uns.ac.rs
Faculty of Technical Sciences
University of Novi Sad, Serbia
2
Abstract: This paper presents an approach to teaching a course dealing with MDE
topics where the focus is on acquiring practical skills. The main goal was to enable
the students to apply the knowlegde from this course in practice after graduation.
This was achieved by directing practical lectures not only to exercising different
MDE techniques, but also to their use in a particular field of software development
– developing business applications.
Keywords: MDE, practical skills, business applications
1
Introduction
In order to survive in competitive markets, globalised economy, and rapid technological changes,
companies – and the software they use – need to be quickly adaptable to changes in their environment [TBK99]. Rapid and cheap software development and efficient adaptation to changes
are requirements that are increasingly often posed to software development teams.
Recognising the needs of IT companies for staff that could satisfy such requirements, the master studies curriculum at the Computing and Control Department, Faculty of Technical Sciences,
University of Novi Sad was extended with the new course titled Rapid Systems Development
Methodologies three years ago. This course aims to introduce students to methodologies and
techniques for efficient software development, mainly Model Driven Engineering (MDE) technologies and agile methodologies. This paper focuses on describing the MDE topics covered by
the course.
The rest of the paper is structured as follows. Section 2 presents information on the background of students attending this course. Section 3 describes an overview of theoretical topics.
Section 4 presents the organisation of practical topics. Section 5 reviews the statistics of the
course held last year. Section 6 concludes the paper.
2
Course Background
Starting from the third academic year, most courses in software engineering and information
systems are organised in an environment that, as much as possible, resembles the real work
environment the students will experience after graduation. Each course comprises theoretical
and practical topics, where the practical assignments are carried out by student teams. A team,
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comprising 3-5 students, is assigned a task of developing a relatively complex software solution.
Development includes modeling, where models are used to specify (pieces of) solutions and fostering the communication among team members as well as the team and the instructor. Team
work is supported by version control software (e.g., Subversion or Mercurial) and the software
for progress monitoring and project management (e.g., Trac). The practical topics usually include solving a (part of a) real world problem, depending on the course. Software design and
implementation in the initial stages are lead by the instructor who participates in specifying the
basic elements of the architecture, while in the latter stages the team operates independently
while the instructor inspects the results and helps the team as needed. The implementation contains unit tests (e.g., JUnit) and documentation (e.g., javadoc). A short video with presentations
of student projects from various courses is available at [Stu].
The most students who attend the Rapid Systems Development Methodologies course also
have attended the following courses: Software Requirements Specification and Software Modeling (introduced right after the courses in OO programming), Compilers, Software Engineering
Topics, Business Information Systems, Net-Centric Computing, Web Services, etc, so they possess the adequate theoretical and practical prerequisites for this course.
3
Course Goals and Organisation
The goal we strive for in the Rapid Systems Development Methodologies course is that students,
while working in almost a real-world environment, realise the power of MDE technologies so
that they may apply their knowlegde later in practice. We have also aimed at providing the
students the sufficient theoretical basis so that they can expand their knowledge of the subject
in their later assignments and master theses. Since the course spans one semester, comprising 3
hours for theoretical topics and 3 hours for practical exercises per week, time limits had to be
considered in order to achieve the ambitious goals of the course.
MDE is a very dynamic field currently consisting of many approaches: Model Driven Architecture (MDA), Model Driven Software Development (MDSD), Executable UML (xUML),
Domain Specific Modeling (DSM), etc. Each of these approaches could be a main subject for
a university course. The dilemma was whether to choose a single approach (which one?) and
study it in detail, or to try to present the students with the overview of the whole field with less
detail.
Since the students not willing to pursue doctoral studies will not have another chance to study
these topics, we opted for the second approach: to provide a broad overview of the field, with
analysis of advantages and shortcomings of different approaches, so that the students can choose
the most suitable one in a particular situation. The lectures were focused on the core ideas,
with less emphasis on formalisms that would require more time to be presented. Each topic was
supplied with references for additional reading and links to university courses that deal with the
same topic in a different way, in order to provide the students with a basis for further research on
a particular topic. The main literature for shaping the theoretical lectures included [SVBS06],
[KT08], [KWB03], [FP10], and [MB02], and OMG documents and standards [Met06], [Obj06],
and [MOF07].
Theoretical lectures introduce students with the following topics:
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Introduction to MDE: an overview, goals, different approaches, models, metamodels,
meta-metamodels (1 lecture)
Introduction to MDA: CIM, PIM, PSM, transformations, MOF, UML Infrastructure and
Superstructure, OCL, XMI (3 lectures)
MDSD and DSLs: graphical and textual DSLs, DSL construction, implementing frameworks and code generators, techniques for combining manually written and generated
code, generation of different artifacts (documentation, tests, installation and configuration
scripts), DSL creation tools (5 lectures)
Executable UML (1 lecture)
Agile methodologies: Agile Modeling, Extreme Programming, Scrum, Lean Software
Development (2 lectures)
The practical lectures were organised so that the students, while developing a real-world
project, gain a deeper understanding of the most of the concepts covered in theoretical lectures
and practical skills in the MDE field. Details on the organisation of practical lectures are presented in the next Section.
4
Organisation of the Practical Lectures
While analysing various university courses with similar topics, we have noted that practical
exercises are usually carried out as a series of small examples illustrating certain theoretical
aspects of MDE, where the course usually ends without an application of MDE to a certain
software development field. However, knowing the possibilities for application of MDE is crucial
if we want the students to use this knowlegde in practice.
Since we are involved in the application of MDE technologies in developing complex business
information systems (for example, see [DMPT10, PMDM11]), the example we have chosen for
the practical assignments is a simplified environment for the model-driven development of threetier business applications, with the usual infrastructure [Fow03]:
data is persisted in a relational database,
data management operations are implemented in the middle tier, and
graphical client application (desktop or web) implements only the user interface and manipulates data by invoking the operations residing in the middle tier.
In their previous courses (Business Information Systems, Net-Centric Computing, Web Services) students have carried out the implementation of this kind of applications through the following steps: (1) specifying the business domain model in terms of UML class diagrams using
a modeling tool (Sybase PowerDesigner [Pow] was used), (2) automatic transformation of this
model into the database model which is used, with some manual optimisations, to generate SQL
scripts, (3) semi-manual implementation of the middle tier (class diagrams are used to generate
Java classes which were manually annotated for Hibernate [Hib]), (4) manual implementation
of the user interface (Swing- or web-based GUI), and (5) manual implementation of complex
business transactions and reports.
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We wanted the students to develop an environment for model-driven development of business
applications that would facilitate automated implementation of all three application layers (excluding the implementation of complex business transactions and reports) and to use it to develop
a small business application (e.g., human resources, stock management) so they can grasp the
benefits and shortcomings of both approaches.
The generation of database schema and middle tier code is supported by a number of tools,
while the generation of the user interface based on declarative specifications is the subject of intensive research efforts [Sil01]. The description of the user interface in the general case uses different types of models (presentation model, content model, navigation model, interaction model,
etc.) but the number of models can be reduced if we target applications with a specific user
interface functionality. In [PMDM11] we have presented a kind of user interface based on our
HCI (human-computer interaction) standard that specifies functional and visual features of different course-grained client application components. For student projects, we have restricted the
component set to the following:
standard data management form (associated to a single entity class or a database table,
providing display, creation, update, removal, and search of the objects of the given class,
traversal to forms of related classes, and invoking the reports and complex transactions –
see Figure 2 and Figure 3),
main form (contains a menu for invoking standard forms), and
parameter form (for entering parameters for transactions and reports).
This way, it is possible to specify a relatively simple user interface language that can be integrated with languages for the specification of other aspects of the system with transformations,
according to the MDA approach, or merging in order to create a comprehensive DSL for desribing business applications, according to the MDSD approach (see Figure 1). During the design of
the language(s) for specifying business applications we have discussed different options. The existence of multiple languages for describing different aspects of the system (Figure 1a) enables
the separation of concerns and the independent work of different kind of specialists, but the
synchronisation of models may introduce an overhead in project development. Discarding the
database model (e.g., using the default object/relational transformation provided by Hibernate)
reduces both the overhead and the number of development options (Figure 1b). If we introduce
the rules like: (1) all problem domain classes are persistent, (2) each association end with the
multiplicity being * is lazily loaded, (3) each association end with the multiplicity being 0..1 or 1
is eagerly loaded, etc, the middleware model is not needed any longer, while all relevant information can be extracted from the business domain model (Figure 1c). Introducing such rules makes
the solution simpler and the development process faster, but reduces the model expressiveness
(which may be appropriate in some situations). In order to prevent the developers feeling too
constrained or too overwhelmed, careful planning is needed. Student teams had to choose their
own strategy and explain their choices.
Since the main topic of this course is not MDE itself, but rather the rapid application development based on MDE, the goal was to model and generate only the elements of the application
for which that approach is more efficient than the manual implementation. The students also had
to decide on the way to reach a balance between automatic code generation and manual coding,
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and to define mechanisms for their integration (based on [SVBS06]). The development method
(of both the tools and the business application) was planned to be in the agile manner, so iterative
and incremental development was assumed where repetitive code generation was not allowed to
damage manually implemented segments.
a)
b)
Problem domain model
«trasformed from»
Database model
Problem domain model
«trasformed from»
«trasformed from»
Middle-tier model
«generated from»
«trasformed from»
«generated from»
«generated from»
Database scripts
Middle-tier model
User interface model
Middle-tier
User interface model
«generated from»
User interface
c)
«trasformed from»
Middle-tier
«generated from»
User interface
d)
Problem domain model
Business Application Model
«trasformed from»
«generated from»
«generated from»
«generated from»
User interface model
Middle-tier
User interface
«generated from»
Middle-tier
User interface
Figure 1: Different approaches to specifying business applications
As a basis for the business application development environment we chose MagicDraw [Mag]
since it is fully UML 2.0 compatible, supports the specification of OCL rules, and is extensible
with plugins written in Java. Plugin implementation uses MagicDraw Open API, a very powerful
library that provides access to the object model representation, changing the model programmatically, developing custom transformations, and customising menus and toolbars. Additional gain
is provided by the already implemented transformations between object and relational models
that can be programmatically invoked. A possible shortcoming is the fact that a DSL can only
be implemented as a UML profile. However, MagicDraw features a DSL Customisation Engine
that enables hiding some UML elements (defining custom toolbars for the new language, customising properties dialogs, specifying new symbols, etc). For transformations from the model
to the program code we used the FreeMarker [Fre] template engine.
The practical lectures were structured as follows:
the development of the problem domain model in terms of class diagrams for stock management (1 lecture)
discussion on business rules for stock management and their specification using OCL (in
order to exercise a specific way of thinking imposed by the use of predicate logic) (2
lectures)
designing the language(s) for business applications design: developing the initial metamodel of the user interface language and the middle-tier language and the discussion on
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different approaches of their integration (students were encouraged to choose the approach
they want and to change metamodels as they see fit), the mapping of the sample metamodel
to the UML profile, specifying choosen OCL constraints, customisation of the UML profile in order to hide unneeded metaclasses and metaatributes (2 lectures)
designing the client application framework based on our HCI standards components: discussion on different approaches, from minimalistic framework where the focus is on the
code generation, to a very complex framework that interpetes the model (or data extracted
from the model) in the xUML manner, techniques for integration of framework and generated code (students could also choose their approach) (2 lectures)
implementation of a MagicDraw plugin and a sample transformation using Open API (for
teams that chose MDA like approach) (1 lecture)
designing the code generator as a MagicDraw plugin (the students were given a simplified
code generator that connected all of the used technologies in order to change and/or extend
it) (2 lectures)
discussion on alternative sources of metainformation (when the model is not available, for
example in an reengineering project): Java reflection, database metadata, etc. (1 lecture)
instructor-supervised development of the environment (3 lectures).
Figure 2: An example of a generated web application (main form and two standard forms)
5
Course Statistics
In the last academic year, 36 students attended the course, grouped into 9 teams. One
student has failed to complete the course.
Two teams have implemented the transformation of the problem domain model into the
user interface model (see Figure 1c), while the remaining 7 teams had one model that was
used directly to generate middle tier and user interface code (see Figure 1d).
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Figure 3: An example of a generated web application (main form and two standard web forms)
One team has implemented a generator of web-based applications, while 8 teams have
chosen to target desktop applications.
One team was focused on the development of a generic framework while generating code
only for EJB entities and form descriptions interpreted by the framework, 6 teams had a
minimalistic framework while the focus was on code generation (over 20000 LOC for a
relatively small business application), and 2 teams have found – in our opinion – a balance
between the use of the framework and the code generator.
Two teams have kept the initially proposed metamodel, while the remaining 7 teams have
improved it.
One team has implemented a parser for simplified OCL expressions in order to generate
derived (calculcated, aggregated, etc) form fields.
No team has managed to fully implement OCL constraints (MagicDraw supports a subset
of OCL, so some correct expressions were not accepted).
The time needed to implement this project ranged from 4 to 6 weeks. The number of
lines of code (code generator, framework, FreeMarker templates) ranged from 4500 to
8500. The initial code generator that was used as a starting point contained 1500 LOC,
so each student wrote about 1000 LOC, which was a moderate sized task. The project of
a generator of web-based applications had the most LOC (8500) because it contained a lot
of artifacts that had to be maintained (JSF was used for the user interface).
Figure 4 presents an SVN statistics of an average student team project. The steep rise of LOC
at the end of the curve stems from committing the generated code and documentation of the
business application into the repository. Although it was emphasized that the generated artifacts
need not be versioned, this curve is useful to illustrate the gain made possible with the use of
automation.
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Figure 4: SVN statistics – LOC for a single team project a) Tool LOC b) Generated application
LOC
The poll taken upon the completion of projects has resulted with the following students’ observations:
The project was not too hard and it didn’t take too much time. Compared to the assignments in other courses, the complexity of this project was rated in the middle.
The course was evaluated with the average mark of 9.93 (5 being the lowest, 10 being the
highest mark).
The importance of the course topics for their future work was rated as high.
6
Conclusions
This paper has presented an approach to conducting a university course dealing with MDE topics
where the focus was on acquiring practical skills. The initial goal set forth, making the students
grasp the power of MDE technologies by working in a real-life environment, is achieved in our
opinion.
Students have showed a satisfactory knowlegde of the field, thanks to the instructor-supervised
work who gave them enough guidelines but also the opportunities for creative work and making
decisions. By implementing the same application in two ways (manually, in previous courses,
and using model-driven techniques, in this course) the students were able to compare the two
approaches, and realise the benefits of the latter. The course has fostered the students’ interest
in the field, and ten students have started the work on their master theses based on the topics
presented in the course: A generic DSL editor, Development environment for end-user specification of static and dynamic aspects of business applications (DSL, editor, framework, generator,
or interpreter) – 3 related theses, Code generator for OCL business rules, Test-cases generator,
Adaptive aspect-oriented frameworks for desktop and web applications (2 related theses), DSL
design time integration, Multiple DSL generator interoperability. The last two theses are being
developed in cooperation with dr Nikola Milanović within the BIZWARE project [Biz].
Acknowledgements:
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This work was partially funded by the grant III-47003 of Ministry of
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Science and Technological Development of the Republic of Serbia.
Bibliography
[Biz]
BIZWARE – Modellgetriebene Softwarekonzeption und -entwicklung.
http://www.bizware.org
[DMPT10] I. Dejanović, G. Milosavljević, B. Perisić, M. Tumbas. A Domain-Specific Language for Defining Static Structure of Database Applications. Computer Science
and Information Systems (ComSIS) 7(3):409–440, 2010.
[Fow03]
M. Fowler. Patterns of enterprise application architecture. The Addison-Wesley
signature series. Addison-Wesley, 2003.
[FP10]
M. Fowler, R. Parsons. Domain-Specific Languages. Addison Wesley Signature Series. Addison-Wesley, 2010.
[Fre]
FreeMarker.
http://freemarker.sourceforge.net
[GP10]
T. Gjøsæter, A. Prinz. Teaching Model Driven Language Handling. Electronic Communications of the EASST 34, 2010.
http://journal.ub.tu-berlin.de/eceasst/article/view/591
[Hib]
Hibernate.
http://www.hibernate.org
[KT08]
S. Kelly, J.-P. Tolvanen. Domain-specific modeling: enabling full code generation.
A Wiley-Interscience publication. Wiley-Interscience, 2008.
[KWB03]
A. Kleppe, J. Warmer, W. Bast. MDA explained: the model driven architecture:
practice and promise. The Addison-Wesley object technology series. AddisonWesley, 2003.
[Mag]
MagicDraw.
http://www.magicdraw.com
[MB02]
S. J. Mellor, M. J. Balcer. Executable UML: a foundation for model-driven architecture. Addison-Wesley object technology series. Addison-Wesley, 2002.
[Met06]
Meta Object Facility (MOF) Core Specification, Version 2.0. 2006.
http://www.omg.org/spec/MOF/2.0/
[MM03]
J. Miller, J. Mukerji (eds.). MDA Guide v 1.0.1. Object Management Group, 2003.
http://www.omg.org/cgi-bin/doc?omg/03-06-01.pdf
[MOF07]
MOF 2.0/XMI Mapping, Version 2.1.1. 2007.
http://http://www.omg.org/cgi-bin/doc?formal/2007-12-01
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[Obj06]
Object Constraint Language Version 2.0. 2006.
http://www.omg.org/spec/OCL/2.0/PDF
[OMG]
Object Management Group.
http://www.omg.org
[PMDM11] B. Perisić, G. Milosavljević, I. Dejanović, B. Milosavljević. UML Profile for Specifying User Interfaces of Business Applications. Computer Science and Information
Systems (ComSIS) 8(2):405–426, 2011.
[Pow]
Sybase PowerDesigner.
http://www.sybase.com/products/modelingdevelopment/powerdesigner
[Sil01]
P. P. D. Silva. User Interface Declarative Models and Development Environments:
A Survey. In Palanque and Paternó (eds.), Interactive Systems Design, Specification,
and Verification. Lecture Notes in Computer Science 1946, pp. 207–226. Springer
Berlin / Heidelberg, 2001.
[Stu]
Student Projects Presentation. University of Novi Sad.
http://youtu.be/M7KCiHT3StI
[SVBS06]
T. Stahl, M. Völter, J. Bettin, B. von Stockfleth. Model-driven software development: technology, engineering, management. John Wiley, 2006.
[TBK99]
D. P. Truex, R. Baskerville, H. Klein. Growing systems in emergent organizations.
Communications of the ACM 42:117–123, August 1999.
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Models and Clickers for Teaching Computer Science
Matthias Hauswirth
Matthias.Hauswirth@usi.ch
http://www.inf.usi.ch/faculty/hauswirth
Faculty of Informatics
University of Lugano, Lugano, Switzerland
Abstract: Many courses in a computer science curriculum, from computer architecture over programming languages to operating systems, discuss complex and
intricate mechanisms and systems. Engineers who develop such mechanisms and
systems (e.g. an operating system) use models to deal with their complexity. Instructors who teach the concepts behind those mechanisms and systems often implicitly
use models to make those concepts more approachable: they present simplified abstractions and draw diagrams to focus on the essential.
In this position paper we propose to make this implicit use of models explicit. We
propose to use models as a teaching tool in all courses where they are helpful, not
just in a course on models or model-driven development. Moreover, we present an
infrastructure, Informa, that provides support for integrating models into an interactive classroom.
Keywords: Models for understanding, technology-enhanced learning, clickers
1
Introduction
Maybe the best way to teach models is not to teach the topic of models. Maybe the best way to
teach models is to teach other topics by using models as an explanatory device. In this paper we
propose to subliminally introduce modeling already in early computer science courses, decoupled from the notion of model-driven software engineering, by creating models when explaining
and analyzing newly introduced concepts, and by asking students to create or transform models
to demonstrate their understanding of such concepts. In the next section we outline the use of
models for teaching one example computer science topic: programming. We believe that the
approach applies equally well to other courses, especially courses related to systems topics, such
as computer architecture, operating systems, compilers, or databases.
2
Example: Using Models for Teaching Programming
“Programming” is one of the central topics in a computer science curriculum. When teaching
students how to program, instructors have to explain the semantics of a given programming
language. Besides giving students a multitude of examples and informal descriptions of the
language’s semantics, textbooks and instructors often also use more formal textual (such as BNF
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Figure 1: Informa problem requiring a student to model the state of a running program
when discussing syntax) or visual (such as flow charts when discussing control flow) modeling
languages.
3
Models in the Classroom with Informa
Brandsteidl et al. [BWH11] have shown the benefit of using innovative teaching approaches for
teaching modeling. A particularly innovative approach that they have not discussed, the use
of classroom response systems (clickers), has been shown [FM06, RPA04] to be beneficial for
teaching a broad range of scientific topics. Clickers are a form of remote controls with a small
number of buttons that all students bring to a lecture. The instructor then poses a (multiplechoice) question, and the students submit their answers by clicking the corresponding button
on their clickers. The instructor’s clicker server collects all responses and provides the instructor (and often also the students, via a classroom projector) with a histogram of the submitted
answers. This use of clickers allows an instructor to immediately check whether students understand the topic she just explained, and it allows students to check their understanding already
during the lecture.
We propose to use clickers for teaching models, and to do so “subliminally” already in early
courses that are not themselves about modeling. To do so, we propose to use Informa [Hau08], a
software-based clicker system that is not limited to multiple-choice questions. Informa allows an
instructor to post arbitrary types of problems, including problems that require students to write
text or to draw graphs. Informa is particularly strong for those kinds of problems that one could
call “model transformations”, where students demonstrate their understanding by transforming
one representation of a concept (e.g., an XML document) into a different representation (e.g.,
a node-link diagram representing the document’s DOM tree). Moreover, Informa’s Solve &
Evaluate approach [HA09, HA11] enables peer evaluation, where students who already have
solved a problem get to evaluate the solutions of their peers.
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Figure 2: Informa problem requiring a student to model the control flow of a program
Figure 1 shows an example of an Informa modeling problem as it could occur in a programming course. Given the Java program on the left, the students have to model its state (by drawing
the diagram on the right), in the form of its call stack frames and its heap objects, at a given point
in time in the program’s execution. In this problem type (which we call “Stack & Heap”), we
do not use UML object diagrams, but we use a visual language introduced in a textbook [BK06]
specifically for modeling the state of a Java program in terms of its stack and heap. The modeling language is limited to the aspects that are essential to the concept being taught, and the user
interface of Informa allows students to efficiently1 draw these diagrams.
Figure 2 shows a different kind of problem type (called “Graph”) supported by Informa. Here
the instructor asked the students to model the given method (left) as a control flow graph (right).
The Graph problem type is more general, because it allows the instructor to define simple metamodels (visual languages based on node-link diagrams with different types of nodes and edges).
This way, instructors can ask students to draw control flow graphs, to draw simple class diagrams
(currently nodes do not support structured contents, so only the class names can be shown), to
draw call graphs, data-flow graphs, DOM trees, or any other type of model representable by
graphs with unstructured nodes and binary links.
Informa supports many other problem types, such as multiple-choice questions, text highlighting, or text editing. Moreover, it is architected as an extensible framework, allowing developers
to implement other kinds of problem types, such as editors for the UML and other modeling
languages.
1
Our students found drawing these diagrams with Informa so efficient that they asked us to provide them with the
corresponding editor so they could also use it to draw such diagrams when taking notes during lectures.
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4
Conclusions
Modeling is a complex intellectual activity. The subliminal introduction of models already early
in the computer science curriculum may turn the creation, analysis, and transformation of models
into a natural activity for our students. Instructors can use models to explain arbitrary phenomena
and concepts in the entire spectrum of computer science courses, and they can ask students
to demonstrate their understanding by creating or transforming models of the concepts under
study. To support this kind of formative assessment using models, we propose to use Informa,
an extensible classroom clicker system that is freely available2 . We hope that the pervasive use
of models, together with Informa, will improve the teaching not just of models, but also of any
other complex concept in computer science.
Bibliography
[BK06]
D. J. Barnes, M. Kölling. Objects First with Java: A Practical Introduction using
BlueJ. Prentice Hall / Pearson Education, 3 edition, 2006.
[BWH11] M. Brandsteidl, K. Wieland, C. Huemer. Novel Communication Channels in Software
Modeling Education. In Dingel and Solberg (eds.), Models in Software Engineering.
Lecture Notes in Computer Science 6627, pp. 40–54. Springer Berlin / Heidelberg,
2011.
http://dx.doi.org/10.1007/978-3-642-21210-9 5
[FM06]
C. Fies, J. Marshall. Classroom Response Systems: A Review of the Literature. Journal of Science Education and Technology 15(1):101–109, March 2006.
doi:10.1007/s10956-006-0360-1
[HA09]
M. Hauswirth, A. Adamoli. Solve & Evaluate with Informa: A Java-based Classroom
Response System for Teaching Java. In Proceedings of the 7th International Conference on Principles and Practice of Programming in Java. PPPJ ’09, pp. 1–10. ACM,
New York, NY, USA, 2009.
doi:http://doi.acm.org/10.1145/1596655.1596657
http://doi.acm.org/10.1145/1596655.1596657
[HA11]
M. Hauswirth, A. Adamoli. Teaching Java Programming with the Informa Clicker
System. Science of Computer Programming, Special issue: PPPJ 2009/2010, to appear, 2011.
[Hau08]
M. Hauswirth. Informa: An Extensible Framework for Group Response Systems. In
Proceedings of the 4th International Conference on Collaborative Computing (CollaborateCom’08). November 2008.
[RPA04] J. Roschelle, W. R. Penuel, L. Abrahamson. Classroom Response and Communication Systems: Research Review and Theory. In Annual Meeting of the American
Educational Research Association. April 2004.
2
http://informaclicker.org/
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Model Correctness Patterns as an Educational Instrument
Azzam Maraee 1 , Mira Balaban1 , Arnon Strum 2 , Adiel Ashrov 1
1
mari, mira, ashrov@cs.bgu.ac.il
Computer Science Department
Ben-Gurion University of the Negev, Beer-Sheva 84105, ISRAEL
2 sturm@bgu.ac.il
Department of Information Systems Engineering
Ben-Gurion University of the Negev, Beer-Sheva, 84105, ISRAEL
Abstract: UML class diagrams play a central role in modeling activities. Given
the difficulty in producing high quality models, modelers must be equipped with
an awareness of model design problems and the ability to identify and correct such
models. In this paper we observe the role of class diagram correctness patterns as
an educational instrument for improving class diagram modeling. We describe a
catalog of correctness and quality design (anti)-patterns for class diagrams. The
patterns characterize problems, analyze their causes and provide repairing advice.
Pattern specification requires an enhancement of the class diagram meta-model. The
pattern classification has a major role in clarifying design problems. Finally, we
describe an actual experiment of using the catalog for teaching modeling.
Keywords: Design patterns, correctness and quality patterns, educational instruments, model and Meta-Model levels, abstraction, visual language, pattern catalog.
1
Introduction
Models are the backbone of the emerging Model Driven Engineering (MDE) approach, whose
major theme is development of software via repeated model transformations. The quality of
models used in such a process affects not only the final result, but also the development process
itself. In order to achieve high quality, it is important to have educated modelers, who are sensitive to model quality. Indeed, similarly to software construction, model quality can be improved
by applying automatic transformations (refactoring), but this approach still cannot replace the
need for good modelers.
Design patterns encapsulate expert advice for solving typical problems that might occur in
multiple contexts. They fulfill an educational role: Awareness of design patterns yields better
solutions. The design patterns trend in software construction gained increasing popularity since
the appearance of the design patterns book of the “GoF” [GHJV95]. On the model-level, there is
research on formulation of software patterns [LP09, BBC08b], formulation of model-level general and domain specific design anti-patterns [EBL11], proposals for design pattern specification
languages [FKGS04, Kim07, BBC08a], and research on the impact of design patterns [TB11].
[EBL10] is a rich catalog of model-level patterns that identify modeling problems.
In this paper we present a catalog of modeling anti-patterns for problems of correctness and
quality in class diagram design [BGU10], and discuss its role as an educational instrument, for
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improving class diagram modeling. Given the widespread usage of UML class diagrams and the
difficulty in producing high quality models, modelers must have deep understanding of model
design problems, their identification and repair. Patterns of correctness and quality problems in
modeling characterize typical situations in which correctness or quality problems arise, analyze
the causes, and suggest possible solutions. Their educational role is to increase the awareness of
designers to inter-relationships between modeling elements that create incorrect or low quality
models.
To the best of our knowledge, this is the first catalog that provides an in-depth analysis of
causes of correctness and quality problems, together with repair advices. The catalog is intended
to play an educational role in teaching object modeling. In view of this goal, we discuss the pattern specification language, the problem-oriented organization of the catalog, and its instruction.
Finally, we describe an actual experiment in using the catalog in teaching modeling.
Section 2 presents a variety of causes for incorrect class diagram modeling. Section 3 discusses the nature of the pattern specification language and presents an enhancement to UML
class diagrams. Section 4 shortly introduces our patterns catalog, and Section 5 describes an
experiment that observes the role of the correctness patterns in teaching class diagram modeling.
Section 6 concludes the paper.
2
Correctness patterns
The two main correctness problems in UML class diagrams are consistency [BCG05] and finite
satisfiability [MMB08]. Consistency deals with necessarily empty classes, and finite satisfiability deals with necessarily empty or infinite classes. Both problems are caused by problematic
interaction of constraints.
Figure 1 presents four incorrect class diagrams, in which the kind of incorrectness problem, or
the kind of problematic constraint interaction vary. Figure 1d presents an inconsistency problem,
caused by the interaction of the disjoint generalization-set constraint, and the multiple inheritance of class C3: The disjoint constraint forces class C3 to be empty in every legal instance.
Figures 1a, 1b, 1c present three cases of the finite satisfiability problem, caused by different
kinds of constraint interaction. In Figure 1a each instance of C has a single successor and at
least two predecessors. Therefore, if the number of C-s in a legal instance is c, and the number
of predecessor-successor links is d, then d must satisfy d = c · 1 and also d ≥ c · 2, implying
the inequality c ≥ c · 2, that can be satisfied only by an empty or an infinite extension of class
C. The problematic constraint interaction in this case involves the multiplicity constraints on the
predecessor −successor association. In Figure 1b the problematic constraint interaction involves
the multiplicity constraints in the cycle of associations w, q, r, and in Figure 1c the problem is
with the class hierarchy between C1 and C, and the multiplicity constraints on the parent − child
association.
Figure 1 shows that correctness problems are varied and can occur for many reasons. We argue
that in real class diagrams it is not easy to understand the various interactions among constraints,
and their impact on correctness or quality. Awareness to patterns that single out problematic
constraint interactions, analyze the problems they create, and suggest possible repairs, improves
the overall design quality.
[BGU10] present a catalog of correctness patterns, that sort out different templates of interac-
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C
{disjoint}
C1
C2
w
-pred 2
2
-succ
C
r
C1
1
1
(a)
1
1
1
q
C2
C3
C3
1
(b)
(c)
(d)
Figure 1: Finite satisfiability problems
tions, characterize the involved problems, and suggest solutions. Each pattern describes a design
problem that is identified by characteristic structures within a class diagram [BMS10].
The class diagrams in Figures 1a, 1b are instances of the Pure Multiplicity Cycle (PMC)
pattern, which characterizes finite satisfiability problems due to interaction of multiplicity constraints on a cycle of associations. Figure 2a informally sketches the identification template of
this pattern. The dashed line indicates a sequence of successive binary associations (the binary
associations path). The pattern includes an additional verification constraint, and analysis of
possible repairs, like relaxing the multiplicity constraint “2” to “1..2”.
The class diagram in Figure 1c is an instance of the Multiplicity Hierarchy Cycle (MHC)
pattern, which characterizes finite satisfiability problems due to interaction of multiplicity constraints on a cycle of associations and class hierarchy constraints. Figure 2b informally sketches
the identification template of this pattern. The two dashed lines indicate an interleaved path of
associations and class hierarchy constraints. This pattern also includes an additional verification constraint, and analysis of possible repairs, like switching the direction of a class hierarchy
constraint in the cycle.
The class diagram in Figure 1d is an instance of the diamond pattern, which characterizes
consistency problems due to interaction between multiple class hierarchy (multiple inheritance)
and disjoint constraints. Figure 2c informally sketches the identification template of this pattern.
A possible repair is to remove the disjoint constraint.
(a)
(b)
(c)
Figure 2: Informal sketches of identification templates of correctness patterns
Correctness patterns as an educational instrument
Using positive examples (like design patterns) or negative examples (like anti-patterns) is an effective educational tool for developing high modeling skills. [BSV09] show that positive exam-
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ples enhance syntactic quality, while negative examples enhance semantics equality, and neither
has much effect on pragmatic quality. While there is an educational value in presenting concrete
examples, patterns provide an abstraction level that classifies the concrete cases along typical
characterizations. [TB11] show the influence of design patterns on improving the inception of
models (although their patterns are presented by concrete syntactic examples).
Correctness pattern abstraction characterizes correctness problems in terms of conceptual
structures such as cycle of associations and class hierarchy cycle, rather than in terms of concrete
examples. Furthermore, patterns provide an accurate specification of problem domains, and solution advices. They can be viewed as anti-patterns that point to negative designs and suggest
repairs. The benefit is twofold: First, they provide a systematic approach for identifying pattern
instances; second, they sharpen the distinction between different kinds of problematic constraint
interaction.
3
Model-Pattern Specification Language
Pattern specifications include desired and undesired structures of elements from the pattern context. Writing a specification demands a language. Pattern writing approaches can be categorized
by two factors: 1) textual notation vs. visual notation (or both); 2) expression at the model-level
vs. expression at the Meta-Model-level. The main mode of usage for patterns is as expert advice
for educational purposes. Formally specified patterns are also used as automatic transformations
(refactorings). It seems that the appropriate mode for pattern expression depends on the intended
usage.
Visual vs. textual specification: Visual notations are uniquely human-oriented representations, that facilitate human communication, comprehension and problem solving [Moo09]. In
contrast, textual representation might provide a better support for rigorous reasoning but is inferior with respect to user comprehension [Kim07]. Indeed, pattern specifications usually employ
some kind of visual representations, usually in an informal manner, using concrete examples.
Good visual representations enjoy the cognitive effectiveness property, i.e., the ability to directly
clarify translations between cognitive and visual concepts [FDCB10]. This property sets a criterion for visual language evaluation [Moo09].
Model-level vs. Meta-model-level specification: In the model-level approach for pattern
specification, patterns are specified using typical examples, that are enhanced with textual specification [GHJV95, LP09]. This is the more popular approach, especially in software design
patterns. Model-level specification proved helpful for communicating design experience to developers. Yet, since structures are expressed via examples and text, it can create ambiguities
that make it difficult to verify conformance to patterns [KE07]. For example, Figure 1a does not
capture the intentioned problem domain, i.e., “finite satisfiability problem due to a cycle of associations with multiplicity constraints” in a way that enables identifying it with the class diagram
in Figure 1b (which belongs to the same problem domain). This approach does not lend itself to
automation of reasoning about patterns.
Meta-Model based specification enables rigorous textual specification of problem domains
that abstract concrete examples [EBL11, EBL10]. The two examples in Figures 1a and 1b can
be captured by a single textual specification, demonstrated in Listing 1 in Section 4. Therefore,
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meta-model-level specification can support pattern automation as refactorings. However, it is
inappropriate for educational purposes, since defining and comprehending the meta-model-level
textual patterns demand expert knowledge.
Conclusion: We argue that for educational purposes, patterns should have visually, hence
model-level specification, but use a notation that captures the meta-model-level abstractions.
For that purpose, the model-level visual language should be enhance with new notation that enables visualization of the meta level abstractions. Below, we describe few extended notation to
the UML class diagrams, that enables visual, model-level specification of the correctness patterns
in our catalog. A similar approach is used in [BBC08a].
Class diagram enhancement for pattern specification: The necessary abstraction involves
constructs for specification of unbounded relationship structures like association paths, hierarchy
paths, interleaved association and hierarchy paths, aggregation paths, etc. We extend the UML
class diagram meta-model with new classes that capture these abstractions, and provide their
concrete syntax as new visual notations in class diagrams.
Figure 3b presents the Meta-Model extension for the generalization path abstraction. The enhancement includes a new meta-class GeneralizationPath, and a derived meta-association nextassoc. Existing meta-model elements appear within dashed rectangles. The new visual notation
for relationship paths uses * for denoting paths of lengths ≥ 0, and + for paths whose lengths
> 0. These symbols are added as labels, on top of the standard relationship symbol. For example, a class hierarchy (generalization) path is represented by a generalization line, labeled by
*. Figure 3a presents the identifying structure for the Multiplicity-Hierarchy-Cycle pattern, that
uses the new generalization-path construct. The concrete syntax enhancement is demonstrated
in Table 1. Figure 4 intuitively sketches a possible instantiation of the identification structure of
the Pure-Multiplicity-cycle pattern.
(a) Identification structure for the Multiplicity Hierarchy Cycle
(b) The Meta-Model enhancement for generalization paths
Figure 3
[Moo09] formulates nine evidence-based principles for achieving cognitively effective visual
notations. Three main principles are: 1) Semiotic Clarity principle – importance of one-to-one
correspondence between semantic constructs and graphical symbols; 2) Semantic Transparency
principle – are symbols and their corresponding concepts are easily associated; 3) Perceptual
discriminability – symbols that represent different constructs should be clearly distinguishable.
We try to follow such principles in adopting new notation. In particular, the use of *,+ labeled
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Graphic notation
Meaning
A path of associations with length is ≥ 0
A path of compositions (aggregation) with length ≥ 1
A path of generalizations with length ≥ 0
An interleaved path of associations and generalizations with length ≥ 0
An interleaved path of compositions and generalizations with length ≥ 0
Table 1: Concrete syntax for relationship paths
Figure 4: Instantiation of the Pure-Multiplicity-Cycle pattern
relationship lines is associated with the traditional meaning of these operators as denoting ≥ 0
and > 0 repetitions, respectively.
4
The Correctness-Pattern Catalog
The catalog includes patterns for solving problems of correctness or of quality of class diagrams.
The correctness problems refer to the two formal correctness problems of consistency and finite
satisfiability. Quality problems refer to formally correct design problems that do not meet criteria
of desirable design. The quality problems are further classified into incomplete design, redundancy problems, and comprehension problems. Within the categories, patterns are classified by
the kind of the constraint interaction that causes the problem. This problem based classification
is contrasted with the approach of [EBL10], which is syntax-semantics-pragmatics based.
Based on the above classification the catalog currently includes a total of 45 patterns: 15
patterns for finite satisfiability problems, 11 patterns for consistency problems and 17 patterns
for quality problems. The catalog is still under development, and new patterns are being added.
Pattern structure: Pattern specification is a template consisting of nine entries: 1. Name;
2. Pattern problem – A textual description of the problem handled by the pattern; 3. Concrete
example; 4. Pattern identification structure – A class diagram snippet in the enhanced class diagram language; 5. Involved meta-model elements; 6. Pattern verification – A formal constraint
imposed on the pattern identification structure that verifies occurrence of a problem; 7. Repair
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advice (refactoring); 8. Related patterns; 9. Pattern justification – a correctness proof for the
pattern identification, verification, and advice.
Example 1 (Pure-Multiplicity-Cycle Pattern)
1. Pattern name: Pure Multiplicity Cycle (PMC).
2. Problem: A cycle of associations with multiplicity constraints might introduce a finite
satisfiability problem.
3. Concrete Example: See Figure 5a.
4. Pattern Identification Structure: See Figure 5b.
(a)
(b)
Figure 5
5. Involved meta-model elements: The meta-classes Association and Class.
6. Pattern verification: The pattern identification structure characterizes a necessary but not
sufficient condition for existence of a finite satisfiability problem caused by the multiplicity
constraints in an association cycle. The verification condition below provides the sufficient
condition. Its specification requires an elaboration of the identification structure, as in
Figure 6.
The cycle causes a finite satisfiability problem if one of the following conditions holds:
n
n
i=1
n
i=1
n
i=1
i=1
• ∏ m0i < ∏ ni .
• ∏ mi < ∏ n0i .
Figure 6: Pattern verification
7. Repair advice: Consider relaxation of the multiplicity constraints: decrease a minimal
multiplicity value or increase a maximal multiplicity value.
8. Related patterns: The Multiplicity Hierarchy Cycle (MHC) pattern.
9. Pattern justification: Proof is omitted.
In order to emphasize the educational value of visual specification on the model level, we
demonstrate, in Listing 1, the textual specification of the PMC identification structure in QVT,
following [EBL10]1 . The specification finds all associations that participate in association cycles.
1
The specification is based on their Classifier Has Generalization Cycle anti-pattern.
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top r e l a t i o n AssociationCycle {
c h e c k o n l y domain s o u r c e a s s o c : A s s o c i a t i o n { a l l c o n n e c t e d a s s o i c a t i o n s −>
i n c l u d e s ( a s s o c ) {}};
e n f o r c e domain t a r g e t c : C a t e g o r y {name = ’ A n t i −P a t t e r n s ’ , p a t t e r n = p :
P a t t e r n {name = ’ A s s o c C y c l e ’ , r o o t B i n d i n g =
rb1 : RoleBinding { r o l e = ’
A s s o c i a t i o n ’ , element = a s s o c }}};}
Listing 1: A QVT based rule for detecting associations that participate in association cycles
5
Putting the catalog into practice
In order to examine the extent to which patterns help in identifying erroneous models, we conducted a series of experiments that check various factors that affect the usage of the correctness
patterns. Table 2 presents the experiment settings: The subjects’ background (Software Engineering and Information Systems Engineering students) and numbers, the education type (by
simple example or by formal and abstract demonstration of the patterns), the domain type (real
or synthetic domains), and the size of the domain and the number of errors.
Exp
1
2
3
4
Subjects
SE (49)
ISE (49)
SE (42)
SE (61)
Education Type
Examples
Examples
SE (42)
Patterns
Domain Type
Real
Synthetic
Synthetic
Synthetic
Additional Factors
Different domain
Different size
Checking Mode
Class Assignment
Class Assignment
Class Assignment
Exam
Table 2: Experiment settings
In the first experiment we divided the subjects into two groups. In the first session (before
introducing the patterns) each group got a different domain model (via a class diagram) of an
academic and a genome domain. In the second session (after introducing the patterns by examples by the paper authors), each group had the other domain model. In each session the subjects
were asked to identify places in which correctness problems occur. The results of the experiment
show that the differences among the subjects’ achievements before and after introducing the
patterns are not statistically significant (see Table 3). Examining the differences across the two
domains does not show any statistical significance as well. Our conjecture is that the students
focused on the domain semantics rather on the model semantics.
These results have led us to perform another experiment that was based on synthetic domains.
Here again, we divided the subjects into two groups, yet the two groups had domain models
with different sizes (with 6 and 2 problems, respectively). We had the same setting as in the first
experiment, in which the subjects had to identify existing problems before and after introducing
the patterns. The results show that in the case of a large domain model with several correctness
problems, there is a significant improvement in identifying the problems after introducing the
patterns (see Table 3).
The third experiment followed the same setting, but the pattern introduction was more thorough, and we provided the subjects with a comprehensive explanation of the notion of correctness
patterns, their formalism, abstraction and the pattern catalog. In this experiment we examined
the improvement in one group and indeed, we found that the achievements made by the subjects
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Exp
1
2
3
4
Before
After
42% (Academia); 49% (Genome);
39%(Genome); 48%(Academia)
28% (6 patterns) ; 52% (2 patterns)
51% (6 patterns); 50% (2 patterns
42%
70%
Precision = 85.57%, Recall = 66.39%
Table 3: Experiment results
were high (70 % identification of the existing problems) compared to previous experiments (see
Table 3).
In the forth examination, we checked the extent to which the patterns help in identifying only
existing problems. For that purpose we calculated the recall measure which is the ability of
the subjects to identify all relevant problems and the precision recall which is the ability of the
subjects to identify only the relevant problems. The results (as appear in Table 3) show that the
patterns indeed provide support for identifying only relevant problems. Yet, their support for
identifying all relevant problems is limited.
Summarizing the results we found out that the correctness patterns indeed provide guidelines
for identifying erroneous models and that their effectiveness increases in cases where the domain
models are complex (and thus have more problems) and when their introduction is presented in
a more formal and abstract form (instead of by examples).
Pattern instruction: Teaching catalogs of patterns or refactorings is hard [Pil10, Kop11]. This
is a well known problem, that results from the monotonic repetitive character of catalogs. Not
surprisingly, we have found through our experiments that we have been most successful when
we taught only one or two patterns out of each category. The problem oriented organization of
the catalog encourages a focused usage, such as when a new kind of constraint is introduced.
6
Conclusion
This paper presented a catalog of correctness and quality patterns for class diagram design, and
discussed its role as an educational instrument. We argued that for educational purposes patterns should be visually formulated, using model-level concepts, and provided an appropriate
enhancement to UML class diagram.
The correctness catalog is still under development. About 30 additional patterns are planned.
In the future, we plan to include the catalog as a routine class material in our object modeling
courses.
Bibliography
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Patterns Against UML Models. Electronic Notes in Theoretical Computer Science
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[BCG05] D. Berardi, D. Calvanese, D. Giacomo. Reasoning on UML class diagrams. Artificial
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D. Kim, C. El Khawand. An approach to precisely specifying the problem domain of
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[Kop11] C. Koppe. A Pattern Language for Teaching Design Patterns. In European conference
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M. Llano, R. Pooley. UML Specification and Correction of Object-Oriented Antipatterns. In ICSEA ’09. Pp. 39 –44. 2009.
[MMB08] A. Maraee, V. Makarenkov, B. Balaban. Efficient Recognition and Detection of Finite
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N. Pillay. Teaching Design Patterns. In Southern African Computer Lecturers Association Conference, SACLA 2011. 2010.
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Threshold Concepts in Object-Oriented Modelling
Ven Yu Sien1, David Weng Kwai Chong2
HELP University College1, Monash University Sunway Campus2, Malaysia
Abstract: Proponents of the object-oriented (OO) paradigm frequently claim that the OO
paradigm is ‘more natural’ than the procedural paradigm because the world is filled with
objects that have both attributes and behaviors. However students in higher education
generally experience considerable difficulty in understanding OO concepts and acquiring the
necessary skills in object-oriented analysis and design. This paper proposes OO modelling to
be a set of threshold concepts and describes a study that sought to improve undergraduate
students’ learning of OO modelling by adopting concept maps as ‘stepping stones’ to facilitate
the development of analysis class and sequence diagrams.
Keywords: Threshold concept, OO modelling, Concept maps, Class diagram, Sequence
diagram
1 Introduction
Object-oriented analysis and design (OOAD) is not easy to learn, and a particular challenge for
students is developing the ability to abstract real-world problems [EMM+06a]. Despite claims
made by advocates of the OO approach [ADS+00], [SBG06] novices in OO techniques in
general have difficulties understanding OO concepts. Colbert [Col94] has found in his
teaching and consulting experience that software developers have problems coping with the
OO paradigm, especially with the concept of abstraction. When trying to conceptualise realworld problems as abstractions within the context of OO analysis and design (OOAD), he
found that software developers experience particular difficulties in trying to classify real-world
objects in generalisation-specialisation hierarchies or whole-part associations.
In this paper we introduce the notion of threshold concepts in OO modelling. A threshold
concept or skill is one which when grasped, changes the way in which the learner views the
discipline or approaches a task; i.e. it is transformative, and is thus likely to be irreversible or
difficult to unlearn. This is certainly true of OO modelling. The journey across a conceptual
threshold is likely to be difficult or troublesome, and may involve traversing the conceptual
space (recursiveness) until ‘the penny drops’. Difficulty may also arise from a concept being
counter-intuitive or contrary to common sense. Threshold concepts are integrative, bringing
together different aspects of a subject that previously appeared unrelated. Finally, a threshold
concept delineates a particular conceptual space, i.e. it has boundaries, and to move beyond
these boundaries the learner needs to grasp other threshold concepts.
The paper is organized as follows: Section 2 describes studies that investigated the problems
novices have in understanding and developing OO models; and research on threshold concepts
within computing education. In Section 3, we present our proposal on OO modelling to be a
set of threshold concepts. Section 4 illustrates some of the difficulties experienced by students
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in OO modelling and Section 5 provides a strategy on helping students overcome the
thresholds. We conclude in Section 6 with a summary of the findings.
2 Background Review
2.1 OO Modelling
During the OOAD phases, models are produced to show the type of information processing
that is required of the new system. A model of an OO system is an abstract representation of
the system. It represents the problem domain and emphasises some characteristics of the realworld. Modelling a system, however, requires the representation of different perspectives or
views of the system and therefore there are different types of diagrams for modelling each of
these views. Models used for OO development can take the form of graphics, narratives, or
formulae.
Proponents of the OO paradigm frequently claim that it is ‘more natural’ than the procedural
paradigm because the world is filled with objects that have both attributes and behaviors.
Neubauer and Strong [NS02] assume that ‘more natural’ implies more intuitive, that is, more
easily understood and more consistent with existing patterns of thought. Martin [Mar93]
similarly notes that we ‘have a natural way of organising our knowledge about the world’ –
hence, we will not find it difficult to ‘analyse the world in a way that seems natural to human
thinking’.
However, although OO is representative of real-world problems, it does not always reflect the
way in which people think [ADS+00], [NS02]. Rosson and Alpert [RA90] reported end-users’
conceptual confusion about objects: OO analysts refer to objects which may not be considered
‘natural objects’ to users. For example, a ‘customer’ may be intuitively seen as a natural object
as ‘it’ can perform some action. But seeing an ‘order’ an entity with responsibilities and ability
to perform operations is likely to be counter-intuitive, possibly requiring crossing a conceptual
threshold. Wirfs-Brock [Wir06] argues that it is a myth that objects in a computer system are
representations of real-world entities – the domain concepts identified in the system are at
‘best loosely connected to their real-world counterparts’.
Bolloju and Leung’s [BL06] study of errors produced by novices in class and diagrams
reported errors to be –
 incorrect multiplicities;
 misassigned attributes;
 incorrect usage of generalisation-specialisation hierarchies;
 missing messages;
 missing objects; and
 incorrect delegation of responsibilities.
An OO system consists of interacting objects to fulfill certain responsibilities. This therefore
implies that objects are ‘animated’ in some way. However, Neubauer and Strong [NS02] argue
that we do not usually view our world as a collection of animated objects interacting with one
another to create processes. Instead, we view our world as containing many inanimate objects
that we control and manipulate. Similarly, Détienne [Det97] conducted a review of empirical
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research on OO design (OOD) and discovered that the results of her research do not support
the claims made for the naturalness and ease of OOD. Some of her findings are:
 The identification of objects from the problem domain is not easy. The entities that are
identified may not necessarily be useful in the design solution.
 The mapping between the problem and programming domains is not easy. The analysis of
the problem domain is not sufficient to structure the solution in terms of objects.
2.2 Threshold Concepts
The notion of threshold concepts was first presented in 2002 at the Tenth Improving Student
Learning Conference in Brussels, and its conceptual framework emerged from the United
Kingdom Economic and Social Research Council funded project ‘Enhancing Teaching and
Learning Environments in Undergraduate Courses’ [DE05]. Seminal work within economics
posited that certain concepts e.g., cost and elasticity held by economists to be central to the
mastery of their discipline could be described as threshold concepts. Subsequent work has
largely focussed on development of the conceptual framework and the identification of
threshold concepts in various disciplines e.g.,
 complex numbers and limits in mathematics [ML03];
 confidence intervals in statistics [CB06]; and
 evolution in biology [TC07].
The following candidate threshold concepts within computing education research have been
proposed:
 OO programming (OOP). This topic has been known to be both difficult to teach and to
learn. Boustedt et al. [BEM+07] identified this to be a broad area within which thresholds
exist. First-year students [ET05] who were interviewed after their first OOP course,
reported that they found OOP to be troublesome to learn (it took a long time to ‘click’),
the knowledge gained is irreversible (once understood the OO paradigm cannot be
forgotten) and transformative (knowledge gained can be transferred to another
programming language).
 Pointers. Boustedt et al. [BEM+07] identified this to be another threshold concept. Firstyear students reported in [ET05] they found pointers to be troublesome to learn (difficult
to understand), the knowledge gained is irreversible (unforgettable); and integrative and
transformative (knowledge gained can be used in other subjects).
 Abstraction. Eckerdal et al. [EMM+06b] identified this to be a candidate threshold
concept as the ability to abstract and to be able to move from one level of abstraction to
another is a key skill in computer science. In a later paper, Mostrom et al. [MBE+08]
suggested that abstraction per se may not be a threshold concept – however, specific
forms of abstraction e.g., modularity, data abstraction, object-orientation, etc. can be
considered as threshold concepts.
 OO at its most basic – including classes, objects and encapsulation [EMM+06b]. Firstyear students [BEM+07] found basic OO troublesome to learn. Learning OO is
transformative (it requires a change in mind-set when viewing OO as representative of
real-world problems) and integrative.
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
Recursion. Rountree and Rountree [RR09] proposed recursion to be a candidate threshold
concept. Many novice programmers have found recursion to be an example of
troublesome knowledge (they have difficulty with the concept of `self reference').
However, once the students have grasped this concept, the understanding is irreversible
(new understanding cannot be unlearnt); and transformative and integrative (the student is
able to identify relationships with other materials e.g. all loops can be expressed as
recursion). Recursion is a boundary marker for both Software Engineering and
Theoretical Computer Science (it is useful in programming, and also defines what is
computable).
3 OO Modelling: Thresholds in OOAD
Undergraduate IT students have in general found difficulty in grasping OO concepts and the
role that UML diagrams play in the analysis and design phases of a software development
lifecycle. It has been observed that students frequently produce class and sequence diagrams
that are incomplete, with many concepts at inconsistent abstraction levels [BL06], [SBG06].
Some of these problems were discussed in Section 2. Most of the students are unable to
effectively build class diagrams from the problem domain because they essentially do not
know ‘what’ to model.
The class diagram is fundamental to the object modelling process, representing the key
concepts and relationships (e.g., generalisation-specialisation hierarchy, aggregation,
composition and association) in the problem domain of the system. The class diagrams
produced during the OO analysis are a logical model and shows classes of objects that are
required to represent the problem domain. The sequence diagram is a kind of interaction
diagram produced during the OO design phase and describes the flow of messages between
objects. It is useful in describing the dynamic design, the invocation of methods, and the order
of invocations.
Several aspects of OO modelling are consistent with the defining criteria for threshold
concepts. The conceptual grasp of OO modelling is difficult to unlearn, it is a solid basis for
effective application, and clearly distinguishes between practitioner and learner.
Simultaneously, OO modelling is difficult both to teach and learn: it represents troublesome
knowledge, not least because of the requirement for abstraction. Modelling is an important
activity in system development: Models represent the system at different levels of abstraction.
OO modelling transforms and integrates understanding of analysis and design of information
systems. This transformative learning produces advanced learners who understand the
complex notions underlying the development of information systems. Topics such as systems
analysis and design, software engineering and advanced topics in OO programming languages
are likely to have little meaning to students who do not grasp OO modelling.
It was previously discussed in Section 2.2, that OOP, abstraction and OO are broad areas
within which thresholds exist. Based on data analysed from student interviews, Boustedt et al.
[BEM+07] argued that more specific threshold concepts in OOP ‘might include the way in
which objects work together (i.e. concurrency), or the ability to see large problems as
composed of a set of small sub-problems’. Eckerdal et al. [EMM+06b] noted in their
experiment that both lecturers and students considered OO as a threshold concept, but the
authors argued that OO is too broad an area and some of the more specific threshold concepts
could be polymorphism or object interactions.
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OO modelling is also clearly a key concept within OOAD, but OO modelling may represent a
family or group of associated thresholds including:
 classes;
 generalisation-specialisation hierarchies; and
 object interactions.
4 Difficulties in OO Modelling
This section presents some examples of the types of problems that novices face when
producing UML class and sequence diagrams:
 identifying classes from functional requirements;
 assigning attributes to a class;
 selecting appropriate generalisation-specialisation hierarchies for classes; and
 assigning responsibilities to objects to realise a use case.
Participants in our study were fifty-one Year 2 IT undergraduate students enrolled in a BSc
(Hons) programme in Computing at two universities in Kuala Lumpur, Malaysia. They worked
on a Vehicle Rental case study containing four expanded use cases (detailed descriptions of
processes) that describe the functional requirements of the system. The participants were asked
to individually produce an analysis class diagram based on all the expanded use cases. Rubrics
were used to describe assessment criteria for evaluating the appropriateness of diagrams,
which were assessed for appropriate classes, attributes, associations and multiplicities.
4.1 Analysis of Class and Sequence Diagrams
The class diagram is the key artefact in the analysis phase as its appropriateness can have a
significant impact on the design of the overall system.
4.1.1 Classes
Liu et al. (2003) observed that the identification of classes is difficult even for experienced
analysts and OO developers, citing three contributory factors complexity, vagueness and ambiguity of natural language;
 lack of the domain knowledge and OO experience; and
 the absence of effective OO methods and well-developed guidelines.
Expected Classes. Table 1 shows the number of expected classes that participants were able to
identify in their class diagrams. Only 8% identified all eight expected candidate classes, 35%
identified seven classes and 2% identify only one appropriate class.
Table 1. Analysis of class diagrams with expected classes
1
2%
1
2
2%
3
8%
Classes1
4
5
14%
10%
6
22%
7
35%
8
8%
Total is not 100% because of rounding errors.
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4.1.3 Generalisation-Specialisation Hierarchies
The role of the generalisation-specialisation hierarchy is usually explained by showing
examples of its use in models that feature common classification hierarchies e.g. Employee,
PartTimeEmployee and FullTimeEmployee. While this approach seems simple, novices
usually find defining hierarchies difficult. Detienne [Det97] finds that novices try to use
inheritance as often as they can, but frequently use it incorrectly, especially when identifying
the static characteristics (attributes) of the superclass and subclasses. She also finds that
novices tend to use the generalisation-specialisation hierarchy to express a whole-part
association. In our study we expected participant to identify a generalisation-specialisation
hierarchy as exemplified in Fig. 1.
.
Figure 1. Appropriate generalisation-specialisation hierarchy
We found that participants’ class diagrams did not include many generalisation-specialisation
hierarchies (Table 2). Only 45% of participants defined appropriate inheritance hierarchies in
their class diagrams; and 6% had a mixture of appropriate and inappropriate hierarchies.
Table 2. Analysis of class diagrams with generalisation-specialisation hierarchies
Inappropriate Use of
Inheritance Hierarchy
12%
Appropriate Use of
Inheritance Hierarchy
45%
Inheritance Hierarchies
not Defined
49%
4.1.4 Object Interactions
Students generally have difficulty identifying messages to be sent in UML sequence diagrams.
They do not know how to fulfil the responsibilities of the use case by getting objects to pass
messages to each other. Students also have difficulty understanding that the interaction
diagrams are dependent on the analysis class diagram in terms of its classes, associations and
multiplicities.
A sequence diagram focuses on the time ordering in which messages are sent. It is useful for
describing the order of invocation of methods. Only 40% of sequence diagrams displayed
some evidence of responsibilities delegated to the appropriate objects. None of the student
diagrams fulfilled all the responsibilities of the use case. 52% of sequence diagrams did not
include any parameters in the messages – we do not however consider this a serious design
fault as parameters can be optionally defined in UML.
4.2 Discussion
‘Completeness of a design is concerned with the fact that the presence of information in some
diagram requires the presence of other information in another part of the design. For instance,
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if there is a use-case that describes some system functionality, then there should also be a
collection of classes that provides this functionality. If some information that we can deduce
from available diagrams is not present in a design, then there is an incompleteness in the
design’ [LCM+03]. By description models produced by our study participants are incomplete
because there are missing elements in the class and sequence diagrams that have not been
defined to represent the requirements of the system.
5 Evaluation: Changes in Levels of Understanding
5.1 Concept Mapping
Concept mapping, a tool for facilitating learning, was developed by Joseph Novak [NC06] at
Cornell University in 1972, and is commonly used for visualising relationships between
concepts. Within the context of OOAD we use concept maps to graphically present
fundamental concepts and their inter-relationships within a problem domain.
Our study (Section 4) initially investigated the difficulties undergraduate students have when
producing UML class and sequence diagrams. The results indicate the fundamental problems
that learners have with OO modelling, and suggest that learners have difficulty with certain
concepts which may represent thresholds in understanding. In order to address these threshold
concepts, a concept-driven approach is developed to help novices produce more appropriate
UML class and sequence diagrams. The effectiveness of this approach is evaluated by three
different experiments.
A static concept map diagrammatically describes the structure of a system by illustrating its
component concepts and their inter-relationships: The concepts thus defined model classes and
attributes in an analysis class diagram. A static concept map is constructed by identifying
concepts and their relationships from expanded use cases, and is built incrementally from the
use cases. Rules for producing a static concept map and transforming it to a class diagram are
defined in [SC07].
A dynamic concept map provides a dynamic view of the system behaviour by showing the key
responsibilities that need to be fulfilled by specific concepts in order to fulfil a particular
scenario of a use case. The concepts defined in the dynamic concept map model objects in the
sequence diagram. For each use case, its key responsibilities are identified and added to the
static concept map so as to produce a dynamic concept map. Rules for producing a static
concept map and transforming it to a class diagram are defined in [SC08].
5.2 Helping Students Through Thresholds
Two studies [Sie10] have reported the effects of using concept mapping to assist learners in
OOAD produce class and sequence diagrams. Some findings of the first study (‘Study 1’),
including common faults found in UML diagrams, are described in Section 4; participants in
this study were not taught any concept mapping techniques. In Study 2 [Sie10] twenty-one
Year 2 IT undergraduate students were taught the concept mapping techniques and this study
found a statistically significant reduction in the number of faults produced in UML class and
sequence diagrams, particularly in terms of:
 identification of expected classes representing the key concepts in the problem domain;
 assignment of attributes to appropriate classes;
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 identification of appropriate generalisation-specialisation hierarchies; and
 assignment of responsibilities to fulfil a particular scenario of a use case.
However the results achieved by Study 2 participants may not be attributed solely to the effect
of concept mapping – other contributory factors to quality improvement include:
 As the students in Study 2 were currently enrolled in an OOAD course, their knowledge of
OOAD concepts and experience in OO modelling was likely to be fresh in their minds.
 The students in Study 2 may have been given a better foundation on OOAD concepts.
 Students in Study 2 were given more time to produce the concept maps and UML models.
Participants responded positively to the use of concept maps: This is consistent with research
[Roy08] reporting the successful use of concept maps in teaching. The results presented in
[Sie10] lead us to conclude that concept mapping has a positive impact on class and sequence
diagram, and suggest that concept mapping effectively helps learners understand OO
modelling. In particular the use of specifically defined labelled links (in the static concept
maps) helps learners distinguish between classes and attributes, and more easily identifies
relationship types. Other particular benefits are that
 mapping is relatively easy to teach; the two types of notations solely used are nodes and
links [NC06];
 maps help clarify the meaning of concepts using propositions [NC06];
 substantial guidelines for producing concept maps have been developed. These are defined
in [SC07], [SC08].
6 Conclusion
In this paper we have proposed the following topics to be considered threshold concepts in OO
modelling:
 Classes. In general, students find this topic to be troublesome (the students experience
difficulties in identify appropriate classes from the problem domain; and assigning
appropriate attributes to classes). The knowledge gained is irreversible (once understood,
it cannot be easily forgotten) and transformative and integrative (knowledge gained can
assist in developing the logical design of databases).
 Generalisation-specialisation hierarchies. Novices usually find defining hierarchies
troublesome (they have problems grouping real-world objects in terms of classification
because they are not used to grouping objects in hierarchies). This is not intuitive enough
to be mastered without training [RA96]. The knowledge gained is irreversible (once the
concept is understood, students will invariably find it easier to identify generalisationhierarchies). This is transformative and integrative as this hierarchy can be used in use
case diagrams and data base models.
 Object interactions. Svetinovic et al. [SBG06] found some common errors committed by
students when producing interaction diagrams:
 assignment of a large business activity to a single object whilst it should be fulfilled
through the collaboration with other objects;
 missing responsibilities that should be assigned to objects; and
 missing objects that should participate in the overall responsibilities.
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This topic has been known to be both difficult to teach and to learn. Students in general
have found this topic to be troublesome to learn (difficult to understand), the knowledge
gained is irreversible (unforgettable); and integrative and transformative (knowledge
gained can be used in OOP).
Meyer and Land [ML03] suggest that once a student has been introduced to a threshold
concept, he/she enters a state of ‘liminality’– a state associated with being ‘stuck’ and not
possessing a mastery of the concept – until the necessary transformation of understanding has
taken place and the ‘threshold’ is crossed. Students who have problems producing analysis
class diagrams will first need to cross the threshold in identifying appropriate classes
(representing real-world objects) before they can assign attributes and relationships (e.g.
associations, generalisation-specialisation hierarchies and whole-part hierarchies) to the
classes. These thresholds have to be crossed before the students can successfully produce
appropriate sequence diagrams.
Studies have been presented to support the adoption of concept maps as aids to novices for
developing class diagrams. Participants in experiments conducted by the first author showed
significant improvement in class diagram construction (after the participants have been taught
the concept mapping techniques), in terms of identification of appropriate classes,
generalisation-specialisation hierarchies, and the appropriate assignment of responsibilities to
objects. When learners have made some progress in OO modelling they are likely to find
drawing concept maps tedious and time-consuming. These techniques are likely therefore to be
important in facilitating conceptual understanding – crossing the threshold of OO modelling.
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R Agarwal, P De, AP Sinha, M Tanniru. 'On the Usability of OO Representations.
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J Boustedt, A Eckerdal, R McCartney, JE Mostrom, M Ratcliffe, K Sanders, C Zander.
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Teaching Modeling—An Initial Classification of Related Issues
Ludwik Kuzniarz, Jürgen Börstler
{ludwik.kuzniarz,jurgen.borstler}@bth.se
School of Computing
Blekinge Institute of Technology, Karlskrona, Sweden
Abstract: Modeling is an important skill needed in both science and engineering
domains. In software engineering, in particular, models are ubiquitous artefacts.
The development, manipulation and understanding of models is therefore an important learning objective. The paper presents the initial results of an attempt that has
been carried out in order to classify issues related to the teaching and learning of
modeling.
Keywords: Modeling, Teaching, Classification
1
Introduction
Constructing and using models is an essential element of any constructive human activity. Models are used for understanding the world around us, as well as for creating new things.
Modeling is therefore an important skill needed in all science and engineering domains. Solving complex problems requires knowledge and skills in modeling, to be able to focus on the
properties that are most relevant in a specific context without being distracted by details that are
irrelevant at a certain level.
In software engineering, in particular, models are ubiquitous artefacts. The development,
manipulation and understanding of models is therefore an important learning objective. However, graduating students have problems with designing even small software systems [EMM+ 06,
LTZ11] and “underestimate the importance of representing structural groupings and interactions
between design parts” [TFB+ 05].
Education related to software engineering, and teaching modeling in particular, is getting increasing attention and understanding in the academic community. The related problems are
highlighted and discussed on fora such as software engineering education related symposia and
workshops. We attempt to provide a classification of issues, problems, and challenges related to
teaching and learning modeling. We claim that the classification will help to better understand
the problems related to teaching modeling, as well as to identify and position existing research
in the area and in consequence to contribute in improving the state-of-the-art of modeling education.
The present paper reports on the first phase of developing such a classification – the elicitation
process and its results, and presents the plans for further research towards a mature and approved
classification framework.
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2
Related Work
There is a large body of work related to a number of aspects relevant for the teaching of modeling. Virtually no work, though, is concerned with categorizations or taxonomies of teaching
issues. Various issues regarding the teaching of modeling were discussed and summarized in
earlier MoDELS panels (see for example [BFG+ 10]), but the results were not categorized in a
systematic way.
Diethelm et alȧnd Schulte and Niere show that UML-like modeling can be successfully introduced in secondary school and helps students grasp basic object-oriented concepts [DGZ05,
SN02]. They especially observe that the models the students created helped them to discuss each
other’s modeling problems.
A general problem of teaching models and modeling is the lack of a commonly accepted
definition of model quality. Nelson et alṗropose a conceptual modeling quality framework where
they integrate product and process views from earlier frameworks [NPGP11].
Empirical research shows that there are various aspects of models that contribute to their understanding, like decomposition quality [BJ08], diagram layout [SW05], naming [BLMM09],
and actual modeling language used [GPS05]. It is therefore important to be aware that there is
no “one-size-fits-all” solution to improve model comprehensibility.
Kuzniarz and Staron propose a number of best practices for teaching modeling/UML and
particularly emphasize the role of consistency between models and iterative teaching [KS06].
The role of model consistency is also highlighted in StudentUML, a teaching tool for UML
diagrams that ensures consistency between class and sequence diagrams [RD07]. Brandscheidl
et alḋiscuss a large scale modeling course with specific emphasis on assessment and propose
different types of exercises for assessing theoretical and practical knowledge and skill in UML
modeling [BSK09].
A good source for teaching or learning issues are typical problems or errors appearing in students’ models or designs. Thomasson et alḟound that many students failed to integrate some
classes into their solutions, i.e. had problems of connecting the elements of a model to a meaningful “big picture” [TRT06]. Another common problem was attribute location or representation,
leading to classes with low cohesion. In another empirical study, Siau and Loo showed that the
problems in learning UML mainly can be grouped into two main categories: (1) problems inherent in UML, like its complexity and semantic issues, and (2) “peripheral” issues, like the
learners’ lacking prerequisites or problems with teaching materials [SL06].
There are also numerous modeling/UML tools1 , but few of them are specifically designed
for teaching. Those tools rarely support easy mechanisms for consistency checking and most
of them have a very steep learning curve. Modern learning environments support features for
collaboratively discussing modeling exercises and solution [BBB+ 10]. Besides reaching more
learners, these tools help students understand that there is no single correct solution to a modeling
problem.
1 The list at http://www.jeckle.de/umltools.htm contains more than 100 UML tools and doesnt’t even include educational tools like StudentUML [RD07] or Violet (http://violet.sourceforge.net).
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3
Initial Classification
A general observation regarding challenges and issues related to the teaching of modeling, is
that some of them share a common denominator, a specific aspect of or a point of view on the
teaching of modeling. We therefore propose a two level classification structure with the points
of view, or perspectives on the top level, and the specific issues on the bottom level (following
the vocabulary used for a similar purpose in [KA11]).
We observed that the perspectives could be characterized by question words and the specific
issues could be elicited by formulating questions around those words in the following way:
why to teach – concerning the reasons for introducing the modeling into the teaching curricula,
Table 1: Initial classification scheme.
Perspectives
W HY:
Why should
modeling be
included in
a curriculum?
W HAT:
What should
be included in
a modeling
curriculum?
H OW:
How should
modeling be
taught?
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Issues
Way of thinking
Problem solving
Successful research
Successful development
Being up-to-date
Being competitive
Creating models
Using models
Informal models
Formal models
Integration of models
Transformation
Code generation
Languages
Tools
Best practices
Basic principles
Consistency
Examples
Exercises
Projects
Industrial practices
Industry lectures
Communication
Presentations
Discussions
Teaching methods
to encourage and stimulate thinking at high abstraction levels
to enable solving problems at higher abstraction level
to enable doing successful research
to enable and ensure successful development of software
to be up to date with recent trends and developments in SE
to be competitive in the labour market
knowledge and skills needed for the creation of models
where and how models can be used
using sketchy drawings to convey basic characteristics or ideas
building models that conform to rigorous formal rules
mixing and merging different models within a project
model transformations
code generation from models
modeling languages and their proper usage
modeling tools and environments that support modeling
proved approaches used in modeling
commonly accepted modeling principles
relationships between different (views of) models
using good examples
actual problem solving
carrying out projects of different size
reflecting practices used in industry
guest lectures from industry
communicating with models
encouraging student presentations
encouraging discussions between students
using specific, dedicated teaching methods and processes
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what to teach – concerning the contents of the teaching,
how to teach – concerning the ways and means used for teaching.
The why, what and how perspectives were the starting point for an initial elicitation of issues
and challenges based on (a) a structured panel discussion on the 8th Nordic Workshop on Model
Driven Software Engineering and (b) interviews with some domain experts. The panelists and
the approached experts were members of academia, who were involved in teaching different
subjects related to software engineering that included elements of modeling. Both groups were
asked the same questions, aimed at finding specific issues in the identified perspectives. The
actual questions were the following:
1. Why do you think we should teach modeling?
2. What should be taught?
3. How we should teach modeling?
The questions represented the identified perspectives. Based on the answers specific issues in
the perspectives were derived, named and described. The resulting initial classification is shown
in Table 1.
In addition to our three initial perspectives, the initial elicitation revealed two additional perspectives that need to be further investigated:
where to teach – concerning the place where the education takes place (e.g., university, on-thejob training etc.), and
when to teach – concerning the time and place in a curriculum (in relation to other subjects).
4
Summary and Future Work
We described the first step of a project aimed at providing a justified and empirically evaluated
classification of the issues and challenges related to the teaching and learning of modeling in the
context of software development, together with the obtained results from that step.
After analysis of the data from the survey, we found that several details of the classification,
concerning both perspectives and issues, need to be further investigated and improved.
In the next step, our goal is to develop an empirically justified classification scheme by targeting a wider population of experts involved in the teaching of modeling. The updated classification will then be extended with empirical data on relative prioritizations of the classified
issues and challenges, using a similar approach as in our classification of consistency problems
in model driven software development [KA11].
Bibliography
[BBB+ 10] J. Börstler, O. F. Bay, M. Baturay, S. Trapp, M. Heintz, S. Weber. embed4Auto:
a PLE for software modelling. In Proceedings of the 15th annual conference on
Innovation and technology in computer science education. P. 322. 2010.
[BFG+ 10] J. Bezivin, R. France, M. Gogolla, O. Haugen, G. Taentzer, D. Varro. Teaching
Modeling: Why, When, What? In MODELS 2009 Workshops. Pp. 55–62. Springer,
2010.
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[BLMM09] D. Binkley, D. Lawrie, S. Maex, C. Morrell. Identifier length and limited programmer memory. Science of Computer Programming 74(7):430–445, 2009.
[BSK09]
M. Brandsteidl, M. Seidl, G. Kappel. Teaching Models @ BIG: On Efficiently Assessing Modeling Concepts. In Proceedings of the MoDELS 2009 Educators’ Symposium. 2009.
[BJ08]
A. Burton-Jones. The Effects of Decomposition Quality and Multiple Forms of Information on Novices’ Understanding of a Domain from a Conceptual Model. Journal of the Association for Information Systems 9(12):748–802, 2008.
[DGZ05]
I. Diethelm, L. Geiger, A. Zündorf. Teaching Modeling with Objects First. In Proceedings of the 8th World Conference on Computers in Education. 2005.
[EMM+ 06] A. Eckerdal, R. McCartney, J. E. Moström, M. Ratcliffe, C. Zander. Can graduating
students design software systems? In Proceedings of the 37th SIGCSE technical
symposium on Computer science education. Pp. 403–407. 2006.
[GPS05]
G. Guizzardi, F. Pires, M. van Sinderen. An ontology-based approach for evaluating
the domain appropriateness and comprehensibility appropriateness of modeling languages. In Proceedings MoDELS 2005. Lecture Notes in Computer Science 3713,
pp. 691–705. Springer, 2005.
[KA11]
L. Kuzniarz, L. Angelis. Empirical extension of a classification framework for addressing consistency in model based development. Information and Software Technology 53(3):214–229, 2011.
[KS06]
L. Kuzniarz, M. Staron. Best Practices for Teaching UML-based Software Development. In Satellite Events at the MoDELS 2005 Conference. Pp. 320–332. 2006.
[LTZ11]
C. Loftus, L. Thomas, C. Zander. Can graduating students design: revisited. In
Proceedings of the 42nd ACM technical symposium on Computer science education.
Pp. 105–110. 2011.
[NPGP11] H. J. Nelson, G. Poels, M. Genero, M. Piattini. A Conceptual Modeling Quality
Framework. Software Quality Journal, pp. 1–28–28, Apr. 2011.
[RD07]
E. Ramollari, D. Dranidis. StudentUML: An Educational Tool Supporting ObjectOriented Analysis and Design. In Proceedings of the 11th Panhellenic Conf. on
Informatics (PCI 2007). 2007.
[SL06]
K. Siau, P. Loo. Identifying Difficulties in Learning UML. Information Systems
Management 23(3):43–51, 2006.
[SN02]
C. Schulte, J. Niere. Thinking in Object Structures: Teaching Modelling in Secondary Schools. In ECOOP Workshop on Pedagogies and Tools for the Learning of
Object-Oriented Concepts. 2002.
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[SW05]
D. Sun, K. Wong. On Evaluating the Layout of UML Class Diagrams for Program
Comprehension. In Proceedings of the 13th International Workshop on Program
Comprehension. Pp. 317–326. 2005.
[TFB+ 05]
J. Tenenberg, S. Fincher, K. Blaha, D. Bouvier, T. Chen, D. Chinn, S. Cooper,
A. Eckerdal, H. Johnson, R. McCartney et al. Students Designing Software: A
Multi-national, Multi-institutional Study. Informatics in Education 4(1):143–162,
2005.
[TRT06]
B. Thomasson, M. Ratcliffe, L. Thomas. Identifying novice difficulties in object oriented design. In Proceedings of the 11th annual SIGCSE conference on Innovation
and technology in computer science education. Pp. 28–32. 2006.
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Position Paper: Software Modelling Education
Martina Seidl12∗ , Peter Clarke3
1 Institute
for Formal Models and Verification, Johannes Kepler University, Austria,
Informatics Group, Vienna Technical University, Austria,
3 Florida State Univiersity, USA
2 Business
Abstract: Model-driven engineering (MDE) is a promising paradigm to deal with
the ever increasing complexity of modern software systems. Its powerful abstraction mechanisms allow developers to focus on the essential challenges hiding away
irrelevant aspects of the system under development. Within the last few years, noticable progress has been made in putting the vision of MDE into practice, where the
activity of textual coding is substituted by modeling. With matured concepts and
stable tools available, MDE becomes more and more ready to be applied in software
engineering projects.
Nevertheless, the best available technology is worthless, if it is not accepted and
used by the developers. Also in MDE profound training is needed to fully exploit
its power. In this paper, we discuss the efforts taken in educational environments to
promote the application of modeling and MDE technologies for the software development process and discuss several challenges which still have to be faced.
Keywords: Software Modeling Education, Computer Science Education Research
1
Introduction
The way how large software systems are systematically developed has been steadily improving over the last decades in order to deal with the increasing size and complexity of such systems [Boe06]. One important driving force for the progressive advancements achieved in the
discipline of software engineering is the concept of abstraction [Jac06] as it can be observed in
the move from machine language to assembly, from assembly to structural high level languages
which finally paved the way to modern object-oriented languages [GJ08]. The object-oriented
paradigm aims at representing domain knowledge about the real world in a manner which is
both natural for the human and easy to process for the computer. Hand in hand with the successful application of object-oriented programming languages is the introduction of object-oriented
analysis and design methods relying on the notion of software models expressed in languages
like the Unified Modeling Language (UML) [BM99]. However, the gap between the design of
a software system and the actual realization introduces the problem of co-evolution. When both
tasks—modeling and coding—are performed, an additional source for errors is introduced, because both sets of artifacts have to be kept in a synchronous state during the complete software
life cycle. As a consequence, the solution is to merge modeling and programing and to provide
∗
Parts of this work have been funded by the Vienna Science and Technology Fund (WWTF) under grant ICT10-018.
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the means to generate executable code automatically from models as proposed by model-driven
engineering [Sch06].
Based on this idea, modeling has experienced an enormous boost not only in academia but also
in industry. With the concretization of the vision of model-driven engineering (MDE), models
are lifted from mere documentation artifacts to full first class citizens in the software development process offering a tool which is expected to drastically change the way how software is
developed. Still, it is a far way to go before the complete software development engineering process can be transformed using MDE techniques. In fact, it is not expected that traditional coding
is eliminated over night, but slowly the new model-driven methods are incorporated to support
programmers doing their work. Since developing software according to the MDE paradigm is
different than traditional software engineering, programming knowledge and experience cannot
directly be transfered to modeling [Fra09] and novel training methods are indispensable.
With this fast evolution of the development methodology, academia is confronted with a severe
problem. On the one hand, students shall be offered profound knowledge on well-established
MDE technologies and approaches, but on the other hand they shall have a competitive knowledge on the state-of-the-art when they leave university. So the question educators are confronted
with is how to judge which approaches have a longer perspective of practical application, and
which ones are only interesting in a short term perspective and will be forgotten when the first
hype is over. This challenge is certainly not new for people who are responsible for the development of computer science curricula. Still there are several areas like theoretical computer science
which are relatively stable, and other ones which are still experiencing an extreme progress such
as the area of software development. Novel technologies can only be applied if people are available who are knowledgable in such technologies, i.e., how to use them properly, otherwise the
benefits are quickly lost and additional complexity is introduced.
In this paper, we give an overview of the activities necessary to train developers effectively in
modeling. Therefore, we first consider the different of areas which cover the wide spectrum of
modeling. Then we review the actions taken in the EduSymp, the premier forum for educators
working in the field of modeling. Finally, we derive a set of urgent open issues.
2
Software Modeling Education
Software modeling education is a very broad topic since modeling can be applied during several
phases of the software development process. In addition, identifying pedagogical techniques
required to train students how to think abstractly while creating models is also a major challenge.
The lack of proper approaches to educating students in software modeling may result in students
creating models that are either not applied in the correct manner, or not being used at all. As
a result, the cost of educating students would not result in any tangible benefits and developers
trained in traditional programming may consider modeling as an additional or even useless task.
In the following, we shall discuss topics which shall be covered by a curriculum in order to
assure that models are applied in the complete software development process.
Introduction to Modeling Languages. Before students are able to apply modeling techniques
in the context of practical software engineering projects, they need to understand the concepts
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of modeling languages, i.e., they have to gain profound knowledge on the syntax and semantics
of modeling languages. For this first step, several different approaches can be taken [EHLS06].
In fact, this shows some similarities with programming education, where a big point of discussion is the language (or even the language paradigm) with which beginners are confronted with.
Modeling may be applied for different purposes like for the description of software systems, for
the description of business processes, database design, etc. One language which covers a very
wide spectrum is the Unified Modeling Language (UML), a general purpose language which was
developed with the goal for supporting as many users’ needs as possible. Therefore, UML is extremely flexible with respect to not only the provided syntactical concepts but also its semantics
being defined over numerous variation points to adapt UML to specific purposes. This plethora
of of concepts and the imprecisseness of the standard usually is a great challenge for beginners
who have to deal not only with a new material, but also with context sensitive concepts. A solution to this dilemma would either be the education of UML using a set of well-defined core
concepts, as proposed in [SHMA08], or to start with a Domain Specific Language (DSL), where
the students get a more focused introduction. Furthermore, the way how a modeling language is
used strongly depends on the application context. Therefore, students have to understand that in
some situations informal descriptions are sufficient whereas in other situations the models have
to provide concise formal specifications.
Dealing with Abstractions. One major issue about modeling is to comprehend how to develop
models at an appropriate level of abstraction. Using the appropriate modeling techniques it is
possible to focus on aspects of the systems those aspects that are not relevant at that time. Using
this approach, the complexity of huge systems can be grasped in a more direct way, because
otherwise it would quickly overwhelm the human intellect. In fact, many programming activities
demand the ability to create abstractions, however, this type of abstraction is different when it
comes to modeling. In programming, abstractions are necessary in order to describe a problem
in such a way that it can be represented by the specific programming language and processed by
a computer. Modeling languages, in contrast, provide the means to describe the world as it is
seen by humans, the step to executable code comes much later. Novices are easily tempted to
put everything into a model or mix the levels of abstractions, making the model harder to read,
harder to use and harder to maintain. Therefore modelers have to be trained to choose the applied
level of abstraction with care [Rob09].
Practical Application. Software modeling is usually done with the intention of building systems that have some practical application. From an educational perspective, building such systems requires that it is not sufficient to learn how to create models on paper, but be able to apply
such modeling skills in practice on real world projects using the appropriate modeling tools.
Using such an approach prepares students to work in industry and to realize software projects
using modeling as a basis. Therefore, a tight integration of modeling into software engineering
curricula is required [CS208]. Models can be applied in many different parts of the software
development life cycle, it is therefore important that students are allowed to learn modeling
techniques by building models for the various phases of the development process. This can be
accomplished in two phases. Phase one involves creating special projects for students tailored
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for didactical purposes and under the guidance of an instructor. Phase two involves applying
the modeling techniques learned to a real world project under the supervision of an experienced
industry trainer. Phase two requires the collaboration with various industry partners. Only with
this background, students become aware of the impact of their modeling activities and how the
quality of a model influences the end product in terms of performance, maintainability, etc.
Model-Driven Engineering. Models can not only be used as design artifacts, but also as substitution of traditional textual code. Then coding activities are replaced by modeling activities.
The executable system is then (semi-)automatically derived from the models. This way of building software requires a new way of thinking from the developers, because again the level of
abstraction is shifted. Now only limited knowledge about computer architecture is necessary,
because such optimizations are performed by the code generators. In order to generate functional
code, a good understanding of the MDE tools is necessary, and in some cases customizations of
the generated code may become necessary for realizing the required functionalities. If the code
is also modified by hand, techniques supporting the co-evolution of code and models have to be
applied, otherwise modifications get lost when the system is rebuilt. Furthermore, since MDE
techniques are at a relative early stage, a profound understanding is necessary for deciding when
the application of which software development paradigm is more appropriate.
Model Engineering. For applying MDE techniques special environments are required. With
the Eclipse modeling framework, a lot of tools are available out of the box. For customization purposes, it may be beneficial to develop dedicated code generators or to implement model
transformation engines which support the conversion between different modeling languages or
rewrite certain modeling concepts. Therefore, it is important to include model engineering in
any software engineering education program. With a deep understanding, how the applied tools
work—which is certainly more easily gained when students develop small MDE environments
on their own (as proposed in [BKSW09]) —it is also easier to apply available tools in the correct manner. Also concepts such as metamodeling and metametamodeling become more natural
when a one has designed and implemented a modeling language and the behavior of code generators is easier to understand when they have been used.
Ideally, industry and academia collaborate for training and education. Whereas industry could
provide practical application scenarios to the university students giving them both a good motivation as well as valuable experiences, the theoretical background could be directly promoted from
research institutions to people working at companies offering the state-of-the-art knowledge.
3
The Educators’ Symposium
The Educators’ Symposium (EduSymp) is an annual event collocated with the International
Conference on Model-Driven Engineering Languages and Systems (MODELS)1 . The goal is
to provide a platform where modeling educators meet, exchange experiences, and develop new
approaches for promoting the MDE paradigm in education. In this section, we first outline the
1
http://www.modelsconference.org
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typical organization of this symposium by analyzing the former six editions as far as the data is
available. Each EduSymp has the focus set on a special issue and some peculiar organizational
highlight. We exemplarily review the last edition of the EduSymp 2010, held in Oslo, Norway.
This analysis of the EduSymp allows us to identify issues which have not been handled so far
and to derive challenges which should be considered in future editions.
3.1
Organization
The EduSymp is always held as a satellite event of the MODELS conference, so it is usually
in parallel either with tutorials and with workshops and may use the infrastructure of the conference. The EduSymp has no budget on its own, so no funding for speakers is available. In
order to successfully hold the symposium, a couple of people are necessary for the organization
as discussed in the following.
Organizers. The EduSymp is organized by one or two researchers/educators working in the
modeling area. The organizers of the next edition are usually announced at the closing session of
the MODELS conference, so the designation usually takes place during the EduSymp. Usually
very active participants are invited to do the organization for the next year. The tasks include
the formulation of the call for papers, the advertisement of the call for papers, the selection of
the program committee members, the guidance of the reviewing process, the notifications of the
authors, etc. In short, the organizers have the typical responsibilities similar to the chairs of a
research event. In the past six editions of the EduSymp, the organization has been done by one
or two professors or associate professors. Additionally, assistants have been involved in some
years. So far, no two editions of the symposium have been organized from the same person
indicating that there is high interest in the community for such an event.
Program Committee. The diagram on the left in Figure 1 shows the ratio between people
from industry and from academia. The majority of the people are working at universities which
is on the one hand no surprise, because reviewing activities are the daily business of academic
researchers. On the other hand, many calls of the EduSymp foster investigations on the synergy
between industry and academia in education and therefore, opinions from people of a practical
background would be extremely valuable. The diagram on the right of Figure 1 indicates the
distribution of the program committee members. In general, people from Europe are dominating. Here it has to be mentioned, that it rarely happens that more than two people from the same
university are involved. The PC members from America are not only from the US, but also from
Canada and countries of South America like Argentina and Brazil. Since modeling research is
done all over the world, as is reflected in the participants of the main conference, and software
engineering is part of almost all computer science curricula, a higher distribution and heterogeneity of papers presented at EduSymp should be possible. Such a mix of papers is preferable
because then different viewpoints could be collected, analyzed, discussed and published.
Participants. Currently no statistics is available on the participants attending EduSymp. From
our experience we can conclude that the EduSymp is mainly visited by the people who actively
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Figure 1: Statistics on the program committee.
contribute to the event, i.e., who present papers (cf. next subsection). Furthermore, there is a
small core of professors who regularly attend the event. For those parts of the symposium where
well known speakers are invited or renowned researchers or educators lead a panel discussion,
the number of participants increases drastically.
Agenda. The EduSymp is a full day event usually consisting of four sessions. In the past, the
symposium usually started with an invited talk, followed by the presentations of the accepted papers, both of short and long papers. Short discussions with the authors are possible. Highlighting
the high interactivity of the symposium, either panels or working group or both are organized
offering room for discussing pedagogical related issues with experts.
3.2
Contributions
The presentations of the peer-reviewed papers constitute an important part of the EduSymp. In
the following, we review the topics for which contributions are invited, the topics of the actual
contributions, and finally we analyze who submits the papers to the EduSymp in order to get an
impression on the audience.
Call for Papers. In general, the EduSymp is intended to provide a forum for educators and
trainers to exchange approaches and experiences on pedagogy for modeling education, experiences with various technologies and tools.
The accepted papers are published in terms of technical reports. In order to increase the visibility, the electronic journal of the EASST2 , an indexed, open access journal, offers a publication
channel since the last EduSymp. The two best papers as well as a short summary are included in
the postproceedings of the MODELS.
Topics of Papers. Table 1 summarizes the types of contributions presented at the various editions of the EduSymp. Please note that for the year 2006 no list of accepted papers was available.
The the first three categories (A, B, C) contain the papers on descriptions and experiences on
2
http://journal.ub.tu-berlin.de/eceasst
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A: Object-Oriented Modeling and UML
B: Modeling and Software Engineering
C: Model Engineering Techniques
D: Abstraction, Design Patterns, Formal Methods
E: Research on Modeling Education
F: Collaboration between Industry and Academia
2005
3
3
0
2
1
0
2007
1
1
0
1
1
0
2008
4
1
1
0
2
1
2009
2
1
1
1
0
0
2010
3
1
2
0
0
1
Table 1: Types of contributions.
courses and curricula, whereas the later three categories (D, E, F) cover the papers on general
methodologies and research on modeling education. Experience reports pose the majority of the
presented contributions, where lecturers report on how they do the teaching. Only two papers
discuss collaboration between industry and academia in modeling education. Topics like tool
support are treated very sparsely. Interestingly, in first years of the EduSymp almost all papers
were about UML related issues which changed over the years. This might be seen as an indicator
how trends in research also influence education.
Authors. The geographical distribution of the authors is shown in Table 2. The majority of the
authors are from Europe, even if the symposium is hosted by a non-European country. Since the
organizers and the PC members are mainly from Europe, maybe the promotion is better in Europe
then in other parts of the world. If between 10 and 15 papers are submitted to the EduSymp, then
it might be considered as a success which might be easily beaten by good workshops. The
problem is that the educators do not have a specific subcommunity in the modeling community
as it is the case for example for model evolution, model verification, etc. Somehow everyone is
involved in teaching, but only very few feel obligated to push education research. It also happens
although not very often that the same author submits more than once to EduSymp.
3.3
Case Study: EduSymp 2010
The first highlight of the EduSymp 2010 was the room filling keynote “Formality in Education—
Bitter Medicine or Bitter Administration” presented by Thomas Kühne where it was illustrated
very vividly how an inadequate presentation of formal methods frightens off students. In the
following sessions seven papers were presented covering innovative education approaches. One
paper of note, which also won the best paper award, was by Brandsteidl et al.[BWH11] where the
usage of novel media like document cameras in modeling education was shown in a live demo.
An online survey conducted prior to EduSymp served as the input for the interactive afternoon
sessions consisting of working groups and a panel. The survey consisting of 18 questions was
launched two weeks before the symposium and promoted via relevant mailing lists. More then
60 persons participated stating how and when they teach modeling. We used the answers for
the categorization discussed in Section 2. Most of the participants use UML or Ecore in their
courses, but also EER, BPMN and a diverse set of DSLs were named. The dominating tool in
modeling education is the Eclipse platform. It showed that educators are in general happy with
the tool support but there are several points of improvements like poor usability, poor support
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Europe
America
Asia
Australia
2005
3
5
0
1
2007
4
0
0
0
2008
8
0
1
0
2009
4
1
0
0
2010
5
0
2
0
Table 2: Geographical distribution of paper authors.
of standards, poor interchange facilities, etc. These issues gave a good starting point for the
discussions led during the EduSymp. Details can be found in the summary [SC11]. Finally, a
steering committee was established to watch and influence the development of the EduSymp.
4
Challenges
We conclude this paper with a set of challenges which are derived from the previous sections of
this paper. These challenges will have to be handled in order to promote modeling education.
Promotion. Unfortunately, teaching has not the same impact as research. Concerning the career in academics, papers on new research results are highly renowned and are important milestones for the CV of an individual researcher. While teaching, on the other hand, it is sufficient
to have a list of courses where some involvement has been taken, so no formal evaluation criteria are available for this thing. This is also the reason why teaching sometime comes up very
short and is often passed to junior researchers. In consequence, courses are often repeated and
innovations are kept at a minimum in order to reduce effort necessary to spend on teaching. This
fact results in a major challenge for EduSymp, i.e., getting more educators involved in research
and publishing in software modeling education. Although the majority of the MODELS’ attendees are involved in teaching, only very few people participate in the EduSymp. Discussions on
teaching are kept very private and so no community collected knowledge is possible.
Repository of Teaching Artifacts. One of the most time consuming tasks in course preparation, is the design of exercises and questions for the tests. The time for this task can be drastically
reduced if good samples are available which have to be adapted to the current context only. Over
the years individual teachers obtain huge local repositories with their exercises, for example if
an exam has to be offered six times per year. An example is the ReMoD-Repository.3
Archival Collection of Knowledge. One of the highlights of the EduSymp are the interactive
sessions with working groups, panels, and open discussions. There, the participants discuss
teaching related topics and develop novel strategies. Unfortunately, the ideas and thoughts are
hardly collected, usually only a short summary is provided by the organizers published on the
three pages included in the collection of the postproceedings of the MODELS satellite events. In
this way, the results of the EduSymp get lost and interesting ideas are never put into practice. To
3
www.cs.colostate.edu/remodd/publications files/ReMoDD-MiSE09.ppt
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alleviate this problem, it would require the organizers to define precise protocols to capture and
store this knowledge in a central repository that is accessible to all modeling educators.
Dedicated Tool Support. One of the greatest challenges educators and students are confronted
with is the handling of the tools. In software engineering hands-on-experience is of particular
importance in order to understand the techniques applied to build software of high quality. Since
modeling is a quite young research area, tools work often well enough to use them in research
projects, but the user has to know how to treat them. So the tools introduce additional complexity
which shift the attention away from the actual problems to be solved. Furthermore, the tools
usually offer too many features distracting the attention from the essential problems to be solved
and the documentation is often insufficient. Teachers, who usually have little or no classroom
support, this problem is a difficult one to solve. Therefore, it would be nice to have dedicated
tool support for education where the environment is tailored and configured to the specific needs
for the specific course. This can be partly be achieved by providing complete Eclipse bundles.
Evaluation Criteria. The output of teaching activities are very hard to evaluate and to compare. In the papers describing courses, typical measures are: the grades of the students, results
of questionnaires where the students had to provide some feedback, which are very often the
subjective impression of the teacher. In order to obtain meaningful results, time has to be spend
on the elaboration of quality measures for models applicable on students’ work.
Industrial Commitment. Education performed at universities is not only done to produce
researchers but also to prepare software engineers and developers for industry. Without close
cooperation with industry, the danger is inherent to produce academics who are able to use the
most recent concepts theoretically, but who have no experience for practical tasks.
Student Involvement. The EduSymp is only attended by educators and trainers, giving students no chance to present their experiences and ideas when they have been recently trained on
modeling. In fact, after a course they should have a profound understanding on the techniques
and tools and they could give good feedback on the pros and cons of the taught content, especially when they did some advanced work in the context of practicals or theses. One reason, why
a student discussion group is not so easy to organize is for traveling the budget is often very low
and that only in very rare cases funding for sending students to conferences is available.
5
Conclusion
The EduSymp is small, well-established event for the promotion of various kinds of modeling
techniques in computer science education. In this paper, we gave a short overview of the past
editions of this symposium which allowed us to derive challenges which will have to be faced in
the future in order to establish modeling as a basic discipline in computer science curricula. We
conjecture that in future only with an adequate understanding of the abstraction power of models,
complex computer systems can be handled appropriately. Therefore, the research community
together with the practitioners from industry must decline the competencies required for the
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efficient application of modeling in the software engineering process. Then it is possible to set
up curricula which cover the wide spectrum of modeling.
Acknowledgements: The authors would like to thank Andreas Winter and Marion Brandsteidl
for their valuable comments.
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