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Re: ISSUE: owl:Class name misleading; try owl:Set?

From: Dan Connolly <connolly@w3.org>
Date: 03 Jan 2003 09:12:14 -0600
To: "Peter F. "Patel-Schneider <pfps@research.bell-labs.com>
Cc: Jim Hendler <hendler@cs.umd.edu>, ziv@unicorn.com, Jeff Heflin <heflin@cse.lehigh.edu>, www-webont-wg@w3.org
Message-Id: <1041606733.22230.20.camel@dirk.dm93.org>

On Fri, 2003-01-03 at 05:49, Peter F. Patel-Schneider wrote:

> > In fact, I asked that it be added to the owl schema:
> > 	owl:Thing owl:disjointFrom owl:Class.
> > 	owl:Thing owl:disjointFrom rdfs:Literal.
> > 	owl:Class owl:disjointFrom rdfs:Literal.
> > and I thought Mike or Pat said they'd do it... or at
> > least think about it.
> 
> This prevents classes from being instances in OWL/Full.

It prevents owl:Classes from being owl:Things;
It doesn't prevent owl:Classes from being rdf:Resources
nor does it prevent rdfs:Classes from being rdf:Resources.

This is by design, no? Perhaps that's not the way other
folks understood the design, but that's what I had in mind when we
closed the layering issue.

In any case, that's what I'm proposing now.


> > Hmm... I don't actually see the constraint that
> > if two classes have the same extension then they're
> > identical, 
> 
> FINALLY!  Then why have you been arguing that it exists?

Because I read the DAML+OIL model theory that way
and I hadn't seen any notice of a change. Sorry,
my mistake.


> > but I also don't see anything that
> > conflicts with adding it.
> 
> Of course you don't.  There is nothing (that I can think of) that would
> cause a semantic extension of OWL to be trivial if (a version of) this
> semantic constraint was added.  This doesn't mean that it is a reasonable
> thing to do for OWL, however.

That it's a reasonable thing to do doesn't follow as a logical
necessity from the fact that it's technically possible, no.

But I think it is a reasonable and useful thing to do, for
other reasons. OWL introduces terminology such as
intersectionOf and unionOf. As was pointed out when
I presented some early model theory proposals, the
traditional usage of "intersection" has exactly
*one* intersection of any classes C1, C2, C3, ... CN.

i.e.
	?I1 owl:intersectionOf (:C1 :C2 :C3).
	?I2 owl:intersectionOf (:C1 :C2 :C3).
	==>
	?I1 owl:sameAs ?I2.

Provided we specify that the domain of intersectionOf is owl:Class,
this is a theorem if we add the extensionality axiom as I'm
proposing.

And indeed we do have such a domain constraint.

<rdf:Property rdf:ID="intersectionOf">
[...]
  <rdfs:domain rdf:resource="#Class"/>

 -- http://www.w3.org/2002/07/owl


>   There are lots of semantic constraints that
> could be added to the OWL model theory that don't cause problems but that
> nevertheless are not in the model theory.
> 
> > Dan Connolly, W3C http://www.w3.org/People/Connolly/
> 
> peter
-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Friday, 3 January 2003 10:12:17 GMT

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