W3C home > Mailing lists > Public > www-rdf-interest@w3.org > November 2002

Re: subclasses (RDF vocabulary definitions)

From: Frank Manola <fmanola@mitre.org>
Date: Fri, 22 Nov 2002 10:13:08 -0500
Message-ID: <3DDE4984.4010200@mitre.org>
To: "Richard H. McCullough" <rhm@cdepot.net>
CC: www-rdf-interest@w3.org, David Menendez <zednenem@psualum.com>, Brian McBride <bwm@hplb.hpl.hp.com>

Richard H. McCullough wrote:

> I don't think intension vs. extension is the issue here; the whole point 
> is that the rdfs:subClassOf property does not rule out the alternative 
> that the two Classes are identical, i.e., subsume the same group of 
> individuals.
>  
> In reality, intension and extension are inseparable.


They may be inseparable, but they're different.  And you've addressed 
the first sentence of my reply:


> 
>     My impression is that the basic problem here is trying to consider
>     subclass as specifying an intensional rather than an extensional
>     relationship.  


but not the rest:

>     In RDFS, a class is a resource that represents the
>     set of
>     things which have that class as the value of their rdf:type property.
>     Given that definition, it certainly could be true that at any given
>     point, the class Man (i.e., the set of things that have class Man as
>     the
>     value of their rdf:type property) could be the same as (have the same
>     members as) the class Animal (the set of things that have class Animal
>     as the value of their rdf:type property).  However, there is no
>     specification that the two classes are (or could be) intensionally
>     identical.  All the Semantics spec (entailment rdfs9) says is that
> 
>     Man rdfs:subClassOf Animal
>     aaa rdf:type Man
> 
>     entails
> 
>     aaa rdf:type Animal
> 
>     It does NOT say that
> 
>     Man rdfs:subClassOf Animal
>     aaa rdf:type Animal
> 
>     entails
> 
>     aaa rdf:type Man
> 
>     Could you cast what you see as the problem is these terms?
> 


To amplify on this a bit, it seems to me that when you say that the 
rdfs:subClassOf property does not rule out the alternative that the two 
Classes are identical, you're effectively saying that it does not rule 
out the entailment, in the above example, that:

      Man rdfs:subClassOf Animal
      aaa rdf:type Animal

      entails

      aaa rdf:type Man

But RDF does not license that entailment.

--Frank




-- 
Frank Manola                   The MITRE Corporation
202 Burlington Road, MS A345   Bedford, MA 01730-1420
mailto:fmanola@mitre.org       voice: 781-271-8147   FAX: 781-271-875
Received on Friday, 22 November 2002 09:56:14 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Monday, 7 December 2009 10:51:57 GMT