Perhaps the best such language for this task would be Smalltalk, since most objectoriented
programmers can learn it quickly, and it allows domain-speci?¬?c constructs to
feel like a natural part of the language.
Several patterns from Smalltalk were indeed used as the basis for OCL from the
OMG (2006). OCL includes Smalltalk-like collection operators for transforming and
?¬?ltering collections, plus a limited set of basic string, arithmetic and collection
operators. It also include some extensions useful for constraints, for example one():
collection->one(iterator | body_expressions)
which returns a Boolean stating whether the body_expressions evaluated to true
for exactly one element of the collection.
While OCL was intended primarily for use in models to specify constraints on
running systems, it can also be used one metalevel higher: in metamodels to specify
constraints on models. As might be expected when a language is used for a somewhat
372 TOOLS FOR DSM
different domain than intended, some tasks have to use a rather low-level approach,
and in other areas the language appears rather bulky. Some tools such as GME or
XMF-Mosaic have indeed found it necessary to invent their own ???versions??? of OCL to
address these problems, raising the question of whether such a language can claim to
be standard anymore.
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