Part11e2: Interfacing (USE/REF) meets SUBTYPE_CONSTRAINT

[Ed Barkmeyer]

Jochen,

> did you in your discussions on interfacing subtype_constraints agree 
> whether they can be USEd, REFERENCEd, or both?

Per clause 11, you can only USE named types (the concept
"instantiation" only applies to types).

The current clause 11 does not allow RULEs to be explicitly interfaced
via REFERENCE, so I don't see why it should allow SUBTYPE_CONSTRAINTs
to be interfaced; they are a kind of global rule.

In my mind, the only Clause 11 issues are: 
- Under what circumstances is a SUBTYPE_CONSTRAINT implicitly interfaced?  
- If a SUBTYPE_CONSTRAINT is interfaced but not all of the entity types 
involved in it are interfaced, what constraint is actually interfaced?

Note that for a RULE, the constraint would only be interfaced if
*all* of the entity types involved in it are interfaced.  But,
because a subtype-expression can include several *separable* constraints,
we have Annex C.  And because SUBTYPE_CONSTRAINT doesn't fix this, we
extend Annex C.

-Ed

-- 
Edward J. Barkmeyer                       Email: edbark at nist.gov
National Institute of Standards & Technology
Manufacturing Systems Integration Division
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