OCL21 — allInstances

It is not entirely clear from the OCL 2.0 specification whether the allInstances operation returns instances of subclasses of the designated type. In other words, it isn't 100% clear whether t.allInstances( ) returns instances of subclasses of t.

Recommendation:

The best solution would be to have two operations, one which returns instances of subclasses and one which does not.

A second-best solution would be to make it clear that allInstances returns instances of subclasses. In this case, an OCL programmer could use the oclIsTypeOf( ) operation as a filter to write a derived operation that does not return instances of subclasses. If allInstances does not return instances of subclasses, it would not be nearly as straightforward to write a derived operation that does return instances of subclasses.

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