Last year I posted UML class diagram that depicts core concepts of REA (resources, events, agents) data model. That’s it:

My colleague had looked at this diagram and said that it’s not canonical UML class diagram, because there is a generalization between associations.

I agree that it’s uncommon to show a generalization between associations in such diagrams. But it’s absolutely legal use of UML. Section 7.3.3 “Association (from Kernel)” of UML 2.0 spec describes semantics and notation of generalization between associations.

UML spec is huge (UML 2.0 superstructure specification has 710 pages), so it describes a plenty of definitions that are not in common use.