Merging subtype constraints (again)

[Ed Barkmeyer]

All,

Phil is correct.  It just goes to show that you should always read all the
fine print carefully.  If I had correctly read Annex B in 1993, I would have
voted No on the DIS.  Annex B.3 rule (b) very clearly agrees with Phil, and
makes Peter's and my interpretation of ABSTRACT SUPERTYPE OF (...)
completely incorrect.  As a consequence, I fully agree that TOTAL_OVER does
something that could not formerly have been done in Express.

Unfortunately, Peter and I thought that what TOTAL_OVER does was possible
with ABSTRACT SUPERTYPE OF.  The problem is that 9.2.4.1 makes ABSTRACT
SUPERTYPE OF exactly equal to the ABSTRACT SUPERTYPE constraint combined
with some impossible to decipher SUPERTYPE OF (...) clause.
The subtypes that appear in the SUPERTYPE OF list have *no meaning* with
respect to the ABSTRACTness.  That is the subtlety that Peter and I missed.

So ignore everything I have said about SUBTYPE_CONSTRAINTS, TOTAL_OVER,
ABSTRACT, SUPERTYPE, etc.  It was mis-informed and entirely wrong.
I have no idea how SUBTYPE_CONSTRAINT interacts with SUPERTYPE OF,
and I don't care.

My operating rule still stands: Use RULEs!  
Never use SUPERTYPE clauses, and don't bother with SUBTYPE_CONSTRAINTS!  
They give you a way to write another 40% of what can be more easily, 
correctly and clearly written with RULEs!  And as Peter has demonstrated, 
they add yet another degree of confusion to the infamous SUPERTYPE clause.

Annex B will have to be modified to accommodate TOTAL_OVER; otherwise
there will be no consistent interpretation of any of this stuff.
My recommendation would be to replace Annex B with an interpretation
of all of the constructs in terms of RULEs, which are in turn based on
set theory, as exemplified in my previous emails and Peter's paper.

-Ed

-- 
Edward J. Barkmeyer                       Email: edbark at nist.gov
National Institute of Standards & Technology
Manufacturing Systems Integration Division
100 Bureau Drive, Mail Stop 8260          Tel: +1 301-975-3528
Gaithersburg, MD 20899-8260               FAX: +1 301-975-4482

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