Introduction
Page 5
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The large number is divided by the modulo (number of groups) of the file. The remainder from the division is the group number.
The entire group is read from disk, and the record is found by searching through the group.
The combination of hashed files and storage of records as variable length strings make for a highly efficient storage and retrieval system. Part 2 of “Getting Started in OpenQM” covers the theory and practice of hashed files in greater depth.
Inbuilt programming language
Many databases (such as mySQL) do not provide a programming language to access or manipulate the data in the database. Rather, they provide an ‘Application Programmer
Interface’ (API) which allows an external programming language (such as Perl, Python, PHP, or Visual Basic) to access the database. This means that programmers can use a language with which they are familiar – if there is an API for that language, and that the database provider does not have to put resources into developing and maintaining a programming language.
Multi-value databases have a different approach. They tend to provide an entire database environment including a programming language and reporting facilities. This is particularly useful for exploiting the multi-dimensional nature of the database.
The actual language provided is a dialect of BASIC. This has been extended to be used with multi-value data in a multi-user environment. It is simple to learn, but contains powerful data and string handling capabilities.
Modern multi-value databases often also incorporate one or more API’s for use with external languages. Typical API’s are for C, Visual Basic, and/or ODBC.
Inbuilt reporting language
Multi-value databases incorporate a combined query and reporting language that allows you to:
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➢ report on data contained in one or more files select records to be reported on (multiple selections)
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➢ sort the data by multiple sort criteria break the data into groups create data columns derived from other data calculate totals, averages, and percentages
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➢ format the data to display in a specified format format the report with headings, footings and page breaks
➢ and more
This is all achieved through a sentence based query language. For example:
SORT INVOICES WITH DATE GE “01-04-2013” AND LE “31-04-2013” BY CUSTNO BREAK-ON CUSTNAME “’UV’”
ENUMERATE INVNO INVDATE TOTAL AMOUNT HEADING “’DGC’Invoices for April 2013’G’Page ‘PL’” FOOTING
“Monthly invoice report” ID.SUP NO.GRAND.TOTAL LPTR
© Rush Flat Consulting Getting Started in OpenQM - Part 1
