On MDA and reverse engineering

This appeared somewhere in a discussion in the MDA forum on LinkedIn:

If legacy code exists, MDA can be used to capture the models from the existing code. Extracting models from legacy code is difficult, but it is much better than having someone go through the code and create a model in their head

I would pose reverse engineering has nothing to do with MDA. MDA is really about transformations in one way only: from more abstract to more specific models (while reverse engineering is the opposite).

I am not saying though that one cannot use models obtained with reverse engineering in a MDA context, but that is out of the scope of MDA. But I’d go as far saying that in the general case reverse engineering is not a good approach for producing platform independent models. Reasons:

  1. good models require care and intent in representing the business rules and constraints in the domain being addressed, and that is really rare to see in handwritten code (Exhibit A: the incipient popularity of Domain Driven Design). If something is not there to begin with, a tool cannot extract it.
  2. manual implementation results naturally in high variability in how the same the domain and technical concerns are addressed (independently and in coordination).

Those two things make it really hard (impossible, I’d say, other than in exceptional cases) for a reverse engineering tool (that is based in some sort of pattern matching) to identify code elements and map them back to platform independent models that are not only accurate and complete, but also well designed.

Reverse engineering can be useful in getting an initial approximation of the PIMs (say, covering structure only, but not dynamics or behavior), but that will require significant manual work to become properly designed models.

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