UMLR — Too much navigability from Generalizations

his is a significant issue with the Superstructure, Classes chapter, PowerTypes package, impacting implementability and consistency between products at different levels of conformance to UML 2.

I propose to simplify the abstract syntax to specify a one way arrow navigating a one-many metassociation from GeneralizationSet to Generalizations that belong to that set. The problem here is very much the same as the problem with dependency, but in a different part of the metamodel.

Figure 18, The contents of PowerTypes package shows a many-many navigable association between GeneralizationSet.generalization and Generalization.generalizationSet.

Problems with this:

1. only 1-way navigation is desired. As toolvendor I don't want to update the Generalization to have any info wrt what if any GeneralizationSets it belongs to. As a user, I do not want the generalization relationship itself, which is very simple in a UML Level 1 product, to be muddied with extra info in a UML product that goes beyond Level 1 by adding support for PowerSets.

2. only 1-many cardinality is desired. Although not navigable, a mapping from generalization to the generalization set is still provided in the metamodel, in a conceptual sense.

Point 2 is consistent with thinking of the specialization classifier in the generalization as being an instance of more than one powertype, because this classifier is just a participant in the generalization, it is the generalization that we want to have a mapping to at most one powertype. The scope of the required change is limited to the text and diagram specifying this metasssociation of GeneralizationSet.