Data Modelling Tutor

The SQL tutor is now in use and seems to be finding favour with students and other tutors. There is a long list of things to add, like the ability to discuss an exercise but the course moves on and now I want to apply the same ideas to the teaching of data modelling. Students often find this rather difficult.

For the past few years we have used an excellent case tool called QSEE, developed by Mark Dixon at Leeds Metropolitan University. We have mainly used this multi-diagram tool for the ER diagrams. QSEE supports conceptual ER models and handles foreign keys, link tables and week entities when generating the SQL DDL. I have a running battle with some other tutors over the use of conceptual ER diagrams versus Relational ER Diagrams, complete with foreign keys and link tables. In my multi-paradigm teaching, conceptual models which treat the later as artefacts of a relational data model makes more sense. Of course I'd like to see a few improvements but sadly development of this tool seems to have ceased. Pity that it hasn't been open sourced.

My teaching emphases the difference between a model and its various representations as diagrams, as text and as code. Since we have already studied XML, it is natural to think of representing the conceptual data model as an XML document and writing the transformations in XSLT or XQuery. Having used Graphviz for a number of years the XML can be transformed to the dot notation to create diagrams in different diagraming conventions. Moreover the goal of providing an interactive data modeling tutor seems more easily realised by processing textual descriptions.

So this weekend, snowed in from work on the boat, I've been working on this tutor and data modelling tool. The really hard part has been to write the model comparator so that differences between a student model and the 'master' model can be detected and explained. This has to take account of variations in the names the student may use as well as differences in order of definition, so a straight XML diff isn't enough. What I have now is not quite right but it will have to be good enough if I want to get this tutor out to students this week.

So here is the link to the index of worksheets so far written:

http://www.cems.uwe.ac.uk/xmlwiki/ER/index.xq?tag=ER

The transformations currently supported include Chen diagrams, ER diagrams with or without attributes, SQL DDL, SQL DDL with foreign keys and many-many resolution, and a rather clunky English text representation.

One feature which was unplanned and just emerged as an obvious addition, was the ability to provide a default model template so the student could solve initial problems by filling in the blanks rather than starting with a blank page.

There is still a lot to do, but I'm pleased to have got the prototype of the ground - a long-held idea finally coming to fruition - made possible by the power of XQuery and the eXist XML database, for which I give thanks to Wolfgang and and the guys every day.