Merging subtype constraints (again)

[Phil Spiby]

Folks,

I was out on Friday and missed some of this argument, but based on what I
can see here...

If motorized_vehicle is in the same scope as the constraint you are trying
to write, then it was combined with the original constraint via ANDOR
anyway, and therefore vehicle&motorized_vehicle WAS in the evaluated set!

Remember that the evaluated set evaluation mechanism considers all members
in a subtype/supertype graph which are visible in the current schema context
when building the evaluated set, not just those with constraints written on
them!

So assuming we have a schema containing:
vehicle,
one_wheel,
two_wheel,
three_wheel,
four_wheel,
motorized_vehicle

The without constraints all the subtypes are ANDOR'd together. If a
constraint is specified, then this constraint is ANDOR'd with those subtypes
not defined in the constraint, i.e.,
ENTITY vehicle ABSTRACT SUPERTYPE OF
  (one_wheel ANDOR two_wheel ANDOR three_wheel ANDOR four_wheel); ...
END_ENTITY;

means
ENTITY vehicle ABSTRACT SUPERTYPE OF
  ((one_wheel ANDOR two_wheel ANDOR three_wheel ANDOR four_wheel) ANDOR
motorized_vehicle); ...
END_ENTITY;

So adding the constraint
 SUBTYPE_CONSTRAINT no_motorized_unicycles FOR vehicle;
  ONEOF (one_wheel, motorized_vehicle);
 END_SUBTYPE_CONSTRAINT;

it would be merged with the above to produce:
 ENTITY vehicle ABSTRACT SUPERTYPE OF
  (one_wheel ANDOR two_wheel ANDOR three_wheel ANDOR four_wheel ANDOR
   ONEOF (one_wheel, motorized_vehicle)); ...
 END_ENTITY;

Which is consistent.

Phil

> -----Original Message-----
> From: owner-wg11 at steptools.com [mailto:owner-wg11 at steptools.com]On
> Behalf Of Ed Barkmeyer
> Sent: Friday, May 10, 2002 8:04 PM
> To: Wilson, Peter R
> Cc: 'wg11'
> Subject: Re: Merging subtype constraints (again)
>
>
> "Wilson, Peter R" wrote:
> >     Ed, in a message to the exploder on 2002/05/08, made a convincing
> > argument that subtype constraint expressions from different
> > SUBTYPE_CONSTRAINTS for a common entity could be merged by ANDing the
> > expressions.
>
> NO!!!  Peter, you misunderstood.  (Probably I was not too clear.)
> I said the constraints can be combined by "LOGICAL AND", like RULEs,
> *NOT* "SUPERTYPE AND".  "SUPERTYPE AND" is *not* LOGICAL (Boolean) AND;
> it is much more like "SET EQUAL".
>
> >     The White Paper on generating long forms stated that in an
> Ed2 to Ed1
> > conversion the constraint expressions should be ANDORed together.
> >
> >     Following Ed's argument, the White Paper should be revised
> to specify
> > AND instead of ANDOR.
>
> The White Paper may need revision (I haven't read it since some early
> draft), but it was my impression that it was to be superseded by the
> forthcoming Annex to Part 11 Ed2, anyway.
>
> But AND is wrong in many cases.  I think ANDOR works correctly for
> joining AND and ONEOF (and ANDOR) subtype constraints into a
> supertype-expression in a SUPERTYPE OF clause.  I'm not sure that
> "joining subtype constraints" by ANDOR (or any other connector)
> is always correct in an ABSTRACT SUPERTYPE OF clause.  The ABSTRACT
> SUPERTYPE OF is declaring a TOTAL_OVER constraint, and if you add
> an ANDOR, you are adding things to the list of subtypes whose
> population union covers the population of the supertype.  In the
> best of cases, the addition doesn't change the TOTAL_OVER constraint,
> but it makes it less clear.  In the worst of cases, it *relaxes the
> constraint*.
>
> For example:
>  ENTITY vehicle ABSTRACT SUPERTYPE OF
>   (one_wheel ANDOR two_wheel ANDOR three_wheel ANDOR four_wheel); ...
>  END_ENTITY;
>
> If I add:
>  SUBTYPE_CONSTRAINT wheeledness FOR vehicle;
>   ONEOF (one_wheel, two_wheel, three_wheel, four_wheel);
>  END_SUBTYPE_CONSTRAINT;
>
> These can be merged by ANDOR:
>  ENTITY vehicle ABSTRACT SUPERTYPE OF
>   (one_wheel ANDOR two_wheel ANDOR three_wheel ANDOR four_wheel ANDOR
>    ONEOF (one_wheel, two_wheel, three_wheel, four_wheel)); ...
>  END_ENTITY;
>
> But if instead I add:
>  ENTITY motorized_vehicle SUBTYPE OF vehicle; ...
>  SUBTYPE_CONSTRAINT no_motorized_unicycles FOR vehicle;
>   ONEOF (one_wheel, motorized_vehicle);
>  END_SUBTYPE_CONSTRAINT;
>
> it would be merged with the above to produce:
>  ENTITY vehicle ABSTRACT SUPERTYPE OF
>   (one_wheel ANDOR two_wheel ANDOR three_wheel ANDOR four_wheel ANDOR
>    ONEOF (one_wheel, motorized_vehicle)); ...
>  END_ENTITY;
>
> And this weakens the original constraint.  The original did not accept
>  vehicle&motorized_vehicle
> as an evaluated set member.  And neither did the subtype constraint.
> Both would require an evaluated set member that contains vehicle to
> contain one of:
>  vehicle&one_wheel, vehicle&two_wheel, vehicle&three_wheel, or
>  vehicle&four_wheel
> But the proposed merge *does* accept
>  vehicle&motorized_vehicle
> as an evaluated set member!
>
> (But ANDing the additional constraint is totally wrong.
>  ENTITY vehicle ABSTRACT SUPERTYPE OF
>   (one_wheel ANDOR two_wheel ANDOR three_wheel ANDOR four_wheel
>    AND ONEOF (one_wheel, motorized_vehicle)); ...
>  END_ENTITY;
> disallows bicycles.  I.e.
>  vehicle&two_wheel
> is not a valid evaluated set member.  One of
>  vehicle&two_wheel&one_wheel, vehicle&two_wheel&motorized_vehicle
> is required.)
>
> -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
>
> "The opinions expressed above do not reflect consensus of NIST,
> and have not been reviewed by any Government authority."
>