I'm working on a model-to-model transformation with UML activity diagram model as a target model. For this reason I'm looking for a activity diagram metamodel. However, my search wasn't really successful. I read a lot of OMG specifications and I'm still confused about the model hierarchy.
I get that the MOF is the metametamodel, but what exactly is the metamodel? Does every UML diagram has the same metamodel?
It's like your grammar book from school: it describes the language you use in the language you use. Kind of a recursive definition. So in order to describe what class, sequence, activity, etc. diagrams (and the concepts behind) mean, it uses exactly those concepts - plus quite some natural text which makes it a bit easier for humans to understand it. In fact, the model itself would (should?) suffice as declarative. But since we are humans and not computers the authors of UML have put lots and lots of plain English text around it.
