UML14 — role concept in UML remains rather vague

Summary: Roles play a dual role in UML. On one hand, a role is the name of an association end [UML, § 2.5.2] and thus nothing more than the name of place of a relation. On the other hand, UML has a notion of roles specified in the context of collaborations [UML, 2.10]. This notion conflicts with the first one since a single role of the collaboration may have different role names assigned by the different associations it participates in. In other words, the associations of a collaboration may assign different role names to their ends (and thus, to the classifiers at the ends) than assigned by the collaboration directly, potentially leading to a clash of role names.

Overall, the specification of the role concept in UML remains rather vague. It seems that classifier roles only indirectly specify the base classifiers whose instances can play the roles: "In fact, since an instance may originate from several classifiers (multiple classification), a classifier role may have several base classifiers." (but where are these specified?) and "However, since the only requirement on conforming instances is that they must have attribute values corresponding to the attributes specified by the classifier role, and must participate in links corresponding to the association roles connected to the classifier role, they may be instances of any classifier meeting this requirement." [UML, 2.10.4]. And finally "Note that the base classifiers of the specialized roles are not necessarily specializations of the base classifiers of the parent"s roles; it is enough that they contain all the required features." This is certainly a very unusual feature in a typed language such as UML.

So what are roles? It seems that in UML they are not types (or classifiers), but a positive definition (other than the equally vague glossary entry) would seem imperative!

resolved