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Reusing language concepts, modular languages

April 05, 2013 10:06:12 +0300 (EEST)

The optional task of Language Workbench Challenge 2013 opens the space for more advanced language designs: It emphasizes modularity of languages and possibility to reuse parts of the DSM solution with a very typical scenario: one language for specifying logic and another for specifying layout.

Having now in my hands the submission of LWC 2013 implementation in MetaEdit+, I played with the combined languages of QL and QLS. QL stands for Questionnaire Language (see earlier blog entry) for defining questions and their sequential order and QLS stands for Question Layout and Style for defining the visual layout of the questions. In the metamodel, implemented by my colleague, these languages (and generators) are tightly integrated.

The combination of the languages allows creating different layout options for the same guestions and their logic. Consider the examples below: questions and question logic can be the same but for layout there are differences - not only for visualization but also for example how the questionnaire is splitted into different pages/steps. Naturally also logic can be different as support for variability space is built directly into the languages.

Two different layouts for the same questionnaire

This kind of integration works usually better than keeping the logic and layout disconnected at design time or using model to model transformations. With this language implementation developers using MetaEdit+ can work in parallel: some focusing on question logic and others on layout - and work seamlessly using the same questionnaire design information on both logic and layoyt. At any point of time either group can also generate and run the questionnaires to try them out. Integrated languages also enable better reasoning, checking and trace among the design elements.

Visit LanguageWorkbenches.net to see the submissions to the third challenge. The website shows also earlier years' submissions allowing you to compare how tools perform and implement the tasks given. I personally have not been involved in organizing these events (just implemented one solution), but what would make me happy in hopefully coming next challenges would be language design tasks dealing with:

  1. Language evolution (so far at LWC languages have been created from the scratch)
  2. Model evolution when DSL/DSM is refined/maintained (so far there has not been interest to maintain models done with earlier version of the languages while this is what happens in practice)
  3. Multiple language engineers (there are often multiple language engineers defining the same language)
  4. Scalability: large models and multiple persons use the language, multiple persons modify the language
  5. Different representations, not only graphical or text, but also matrixes, tables, and their mixtures

While this year looked more like framework and runtime development challenge than language development challenge (my colleague estimated only 20% to language development part in MetaEdit+), perhaps even bigger differences among the language workbenches would be visible when implementing larger languages - integrated and obviously modular. Join LWC 2013 next week to see how all the solutions work.