XMI12 — DTD generation rules for composed Packages.

The DTD generation rules do not adequately cover Package importing,
clustering and inheritance.

1) There are no references to clustering anywhere in the DTD
generation rules.

2) There are allusions to the XMI.import element in Chapter 6 but no
proper explanation of how it is used. Other points need to be
clarified. For example, I can't work out how the DTDs allow you
to represent an instance of metamodel Class which has an Attribute
whose type is an imported Class.

3) Package inheritance seems to be covered in the EBNF for DTD
generation and the corresponding pseudo-code. However, the
terminology is loose; e.g. refering to "Packages from which
this Package is derived" without stating whether "derived"
refers to the MOF::Model::Generalizes association.