MOF14 — Restrictions needed for nested Packages and Classes

In recent MOF RTF telcon discussions, we tentatively concluded that we need
Constraints on the MOF Model to forbid 1) clustering of nested Packages,
2) inheritance of nested Packages and 3) clustering of Classes.

Additional Text:

There are three arguments for the proposed restrictions. The first
argument is that supporting inheritance / clustering in these cases adds
to the complexity of MOF implementations. Since practical metamodels
never seem to use these combinations of features, it is hard justify
supporting them.

The second argument is that clustering and inheritance of nested
Packages is problematical. The elements of a nested Package are
implicitly defined in the context of the nested Package's outer Package.
A Constraint or Operation defined on / within a nested Package may
reasonably refer to Associations or "all_of_*" collections in the
enclosing context. When a nested Package is inherited or clustered
outside of the context of its parent Package, the Constraint and
Operation semantics may cease to be meaningful.

The second argument does not apply to a nested Package that is
inherited by another nested Package with the same outermost Package.
However, we have not been able to identify a use case for this sort
of thing. Hence the first argument applies.

The third argument is that the MOF IDL mapping explicitly excludes all
of these cases; see "Section 5.5 - Preconditions for IDL Generation".