UML14 — MOF rules should disallow certain composition relationships

MOF rules should disallow composition relationships in instance metamodels
where the container is in one MOF Package and the contained item is in
another MOF Package and a dependency of the first package on the second is
not allowed by the physical version of the metamodel due to MOF-imposed IDL
generation rules.

Reason for the issue:

In the process of implementing an XMI-based interchange for UML 1.3, I have
encountered a serious problem.

This problem has to do with a divergence between the "Logical" and
"Physical" model for UML 1.3 caused by rules imposed by MOF.

In particular, in section 5.5 of the MOF 1.3 specification (27 Sep 99
version), "Preconditions for IDL Generation", requires that there be no
cyclical dependencies between ModelElements in a meta-model.

However, the UML 1.3 specification (June 1999) has a cyclical dependency
between the Core and the Extension Mechanisms packages in the metamodel (See
Figure 2-4). This cyclical dependency is explicitly disallowed by the
precondition cited above.

This circular dependency was removed from the "Physical Model" for UML 1.3
in order to allow CORBA IDL and XMI DTD declarations in conformance with the
precondition. As a result of the removal of this dependency, there are
tremendous difficulties expressing the composition relationship between the
UML ModelElement and the UML Tagged Value (see figure 2-10). In fact, the
TaggedValue XML elements cannot even be in the exported UML Package element
– they must be placed outside of it. This greatly complicates the export
and import of UML 1.3 model files.

No Data Available