Necessity of Part 25 change supporting ONEOF?

[David Price]

Part 25/EXPRESS/UML Folks,

At the Charleston ISO meeting I was given the following change to make to
Part  25:

"5 - Make EXPRESS ONEOF an explicit UML disjoint constraint between subclasses of a
common UML Class representing an EXPRESS entity that is a supertype when specified
in the EXPRESS supertype constraint."

After reviewing the UML 1.3 spec further I think this change is not
necessary. In fact, if we do anything we need to add "overlapping" in the
case where no SUPERTYPE constraint is specified.

Here's what UML 1.3 says about : Generalization

A generalization is a taxonomic relationship between a more general element
and a more specific element. The more specific element is fully consistent
with the more general element (it has all of its properties, members, and
relationships) and may contain additional information. In the metamodel, a
Generalization is a directed inheritance relationship, uniting a
GeneralizableElement with a more general GeneralizableElement in a
hierarchy. Generalization is a subtyping relationship (i.e., an Instance of
the more general GeneralizableElement may be substituted by an Instance of
the more specific  GeneralizableElement). See Inheritance for the
consequences of Generalization relationships.

Here are two of the Standard Constraints that can be applied. Note that
"disjoint" (i.e. ONEOF) is the default!

disjoint

Specifies a constraint applied to a set of generalizations, indicating that
instance of the parent may be an instance of no more than one of the
given children within the set of generalizations. This is the default
semantics of generalization.

overlapping

Specifies a constraint applied to a set of generalizations, indicating that
an instance of one child may be simultaneously an instance of another
child in the set (but there is no guarantee that such an instance will
actually exist).

Opinions on what do to? I think either 1) do nothing or 2) add overlapping if no supertype constraint at all, but let's not try and
figure out the complete set of permutations.

Thanks,
David

IBM Corporation
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