[mdt-uml2.dev] OCL and UML run-time alignment

[Ed Willink <ed@xxxxxxxxxxxxx>]

Hi All

OCL 2.0, 2.1, 2.3 has an outstanding issue to achieve UML alignment. 
There are significant difficulties in aligning OCL's M1/run-time type 
system in which everything conforms to OclAny, and the OCL/UML 
M2/meta-modelling type system in which everything has Element as a general.

OCL's need to mutate the user meta-model by insertion of OclAny at the 
top of the class hierarchy and to merge definition constraints makes it 
difficult to achieve the desired alignment without modification of UML 
specifications.

MDT/OCL has many outstanding bugs relating to inadequacies and 
inaccuracies of the OCL Standard Library that supports the run-time type 
system.

It appears that the attempt to align OCL run-time with UML is misguided; 
the conformance relationship is similar but not the same as the 
generalisation relationship. The OCL run-time model is much simpler than 
UML classes; no associations or references, but also more complicated, 
three variants (built-in, meta-modelled and constrained) of operations 
and properties.

Introducing a distinct run-time meta-model appears to solve all the 
problems. The OCL standard library can then be a true model, and 
alternative models can be provided for variant behaviours e.g. MDT/OCL 
1.3.0 rather than MDT/OCL 3.0.0 or QVTo 2.0 or ...

From the MDT/OCL side this is a major simplification and enhancement 
and eliminates the exposure of the Ecore/UML2 tooling distinction to OCL 
programmers. However, I have very limited familiarity with MDT/UML2 so 
cannot be sure whether this simplification has any impacts on MDT/UML2.

Does UML or MDT/UML2 have any significant run-time artifacts other than 
those provided by OCL?

A side question; can you confirm my interpretation of the UML 
specification that the semantics of operation overloading are a semantic 
variation point and that consequently the semantics of operation 
overloading in OCL are undefined?! If OCL has its own run-time 
meta-model, OCL can at least define this.

    Regards

        Ed Willink