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Re: cycles in rdfs:subClassOf, cyc gels, extensionality of classes

From: Daniel Mahler <mahler@cyc.com>
Date: Wed, 27 Jun 2001 14:58:42 -0500
Message-ID: <15162.15090.175059.460880@mcallister.cyc.com>
To: Dan Connolly <connolly@w3.org>
Cc: Daniel Mahler <mahler@cyc.com>, Stephen Reed <reed@cyc.com>, www-rdf-logic@w3.org

Dan Connolly writes:
 
 > > This a genral point for clarification:
 > > do RDF(S) entities also exist in the DAML namespace.
 > 
 > I can't give a clear answer to that question as stated;
 > by analogy, it looks like:
 > 
 > 	are integers in decimal or hexadecimal?

What I was asking was simply if whenever you have
&rdfs;Tag you also automatically have a &daml;TAG
with an implicit equivalentTo assertion,
unless we choose to tweak the semantics,
in which case you have the &daml;TAG and no equivalentTo assertion.
This would make it easier to write DAML ontolgies
with the DAML NS as default and only worry about
keeping the the domain level NSs straight.

 > Integers can be denoted by either sort of number,
 > and the concept of subclass can be denoted by
 > any number of names.
 > 
 > You might ask if the names/terms/URIs used in the RDFS
 > spec are also used in the DAML spec; as I said
 > above, the Oct 2000 DAML spec had synonyms for RDFS terms,
 > but the Dec 2000 and Mar 2001 specs do not.

Ah, that answers my question.

 > More on the substantive issue separately...
 > 
 > >  > But more substantively... because cyc's genls is
 > >  > explicitly *not* extensional, and rdfs:subClassOf,
 > > 
 > >  >
 > > 
 > > As I understand it,
 > > in Cyc genls is extensional,
 > > 
 > > (genls A B) is just a macro for
 > > (forall ?x (isa ?x A) (isa ?X B)).
 > > 
 > > Collection/Class identity is not.
 > 
 > I'm baffled by that. I'll have to think about it.

It just means that (in a a Cyc/KIF creole)

(<=> (and (genls A B) (genls B A))
     (coExtensional A B))

but NOT:
   
(=> (and (genls A B) (genls B A))
     (equals A B))   

ie it is NOT the case that

(=> (and (isa A Collection)
         (isa B Collection)
         (forall ?x
                 (<=> (isa ?x A)
                      (isa ?x B))))
    (equals A B))

which is what is understand to be the usual definition
of extensionality.

D

 > -- 
 > Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Wednesday, 27 June 2001 15:58:45 GMT

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