XMI12 — Representing object references in an XMI document

Suppose that a meta-model is declared as follows:

package Foo {
class Bar

;
};

According to the XMI document production rules, the value of the "baz"
attribute should be encoded using the ObjectReference production (9.4.5.2).
This says that if the object is part of the model (e.g. an instance of
some Class defined by the meta-model), the value is encoded as:

XMI.reference xmi.idref="some_id" /

Otherwise it is encoded as

XMI.reference href="some_URL" /

Unfortunately, the latter does not work because there is no legal URL
representation for a CORBA Object reference, and you can't represent
a CORBA Object reference in some other XMI document.

I think the fix is to provide a third alternative:

XMI.reference stringified-CORBA-IOR /XMI.reference

Close with no action because of updates to MOF 1.4 datatypes