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by Martin Fowler.
Original Post: MDSDandDSL
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It's pretty common to see the term "DSL" crop up in the context
of MDSD. Indeed some MDSD people seem to think that DSLs only exist
within the MDSD world. I've been writing a lot on DSLs recently for
my book, but so far I haven't really touched on the MDSD angle much
Instead I've concentrated on DSLs role in more conventional
programming. DSLs exist in both the textual language and MDSD worlds
and play pretty much the same role for both.
In an MDSD context DSLs are again a language targeted at a
specific kind of problem as opposed to general purpose languages
such as the UML. As a result they can have the same kind of
relationship: build a system in the general purpose modeling
language and use DSLs for various specific aspects. Since MDSD
hasn't caught on that much, however, you also see a different
approach where modeling DSLs are used in the context of a
traditional language environment. Here you might use several
modeling DSLs that generate Java code to be combined in a Java
project. In this case there's no general purpose MDSD model around -
you use MDSD for each DSL relatively independently.
In order to use model-oriented DSLs you need a different,
RepositoryBasedCode,
approach to tooling. This introduces quite a few pragmatic issues as
the general support environment for such tools is less
established. In order to define your own DSLs you need more
specialized tooling - something I call a Language
Workbench.
DSLs seem to have a proportionately higher emphasis in the MDSD
world than they do in the mainstream programming world. Cynics think
this is a result of the MDSD community desperately searching for a
way to remain relevant, fans of MDSD regard it as a sign of MDSD's
superior sophistication. I think this is mainly due to the fact that
the MDSD community is smaller and has far less in the form of
established practice.
A particularly visible sub-community of MDSD is centered around
ModelDrivenArchitecture (MDA). I'm not much of a fan of MDA in
particular, but am particularly
skeptical of MDA DSLs.
There is much that model-oriented DSLs share with textual DSLs. I
put a lot of emphasis with textual DSLs in basing work around a
Semantic
Model. MDSD, as its name indicates, is very much about driving a
system from that kind of a model. A difference is that most MDSD
people assume that you'll want to generate code from that model
rather than executing the model directly.
As I write this, I'm not sure how much I'm going to cover
language workbenches in my book. Certainly I'll at least discuss the
overall concept behind them, but the coverage may not be that
deep. This will be partly due to the large amount of material I seem
to be generating on textual DSLs and partly due to the fact that
language workbenches are much newer and thus more volatile and less
mature.
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