Unified Process and UML confusion

Question

Hi

Im a bit uncertain about the relation between the Unified Modeling Language (UML) and the different modelling perspectives (conceptual, specification and impelementation) endorsed by (R)UP among other OOA/D methodologies.

From what I understand the same type of diagram using the same notation can have different meaning depending on the perspective* being used. For instance the class diagram can represent an abstraction of real world systems / phenomena in the conceptual perspective and when perspective is later changed to specification/implementation the class diagram is used to abstract constructs of a computer program.

Questions:

1) It is my understanding that certain rules exist for a UML class diagram in general. For instance that a class can extend another class but that it can't extend an association. Where are the entities of the class diagram and the rules about how they can relate defined? Does it all take place at the M2 layer in the UML metamodeling architecture (see wikipedias illustratio of metamodel architecture)?

2) A related question. The way I see it, the general rules for a specific diagram span the modelling perspectives (again, it is absurd for a class to extend an association), but the different modelling perspectives will superimpose certain meaning to a particular type of diagram. For instance an association in the class diagram of the domain model (conceptual perspective) will inherently be bidirectional whereas it can be either bi- or unidirectional in the class diagram of the design model (specification / implementation perspective).

In the scenario just described the rule superimposed limits the properties of an association. Is it a correct assumption that rules superimposed by perspectives will always be a subset/limitation of the rules defined by the uml metamodel and never a superset?

Are these rules/limitations defined by the perspectives formalized (in a way similar to the metamodel) or are they mere conventions described in the OOA/D litterature?

* Perspectives are explained in paragraph 10.8: http://books.google.co.uk/books?id=r8i-4En_aa4C&printsec=frontcover&hl=da&source=gbs_v2_summary_r&cad=0

Answer 1

1) Your first question is quite clear. The rules that you are looking for are called a "metamodel". And yes, they are documented as what the OMG (the creators of UML, basically) call "MOF" or "meta-object facility". It is an OMG standard.

2) Your second question is a bit more confusing. I'll try to answer here. Diagrams are just views on an underlying model. The model is overarching and all-encompassing, if you wish. But diagrams are not. The perspectives that you mention are related to diagrams. But the model that underlies is multi-perspective, in the sense that all the elements form a connected mesh, without isolated "islands". Does this make sense? :-)