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Re: subclasses (RDF vocabulary definitions)

From: Richard H. McCullough <rhm@cdepot.net>
Date: Fri, 22 Nov 2002 09:57:00 -0800
Message-ID: <002701c29250$8f0f9fc0$bd7ba8c0@rhm8200>
To: "Frank Manola" <fmanola@mitre.org>
Cc: <www-rdf-interest@w3.org>, "David Menendez" <zednenem@psualum.com>, "Brian McBride" <bwm@hplb.hpl.hp.com>
In enumerating the alternatives, I am NOT talking about

    aa rdf:type Animal  entails  aa rdf:type Man

I am talking about

    Man  rdfs:sameAs  Animal

My mention of extensions (sets) was only an attempt to concretize the discussion to make the argument easier to understand.  Apparently, my attempt produced more confusion.

One other point is confusing me here.  You seem to be saying that rdf:type is part (or all) of the intension.
I understand intension to be the properties of a Class, while type is essentially just the bookkeeping
that records the result of examining the properties of an Individual, and classifying it as a member of
a particular Class.  Is type sometimes/always considered to be part of the intension?
============ 
Dick McCullough 
knowledge := man do identify od existent done
knowledge haspart list of proposition

  ----- Original Message ----- 
  From: Frank Manola 
  To: Richard H. McCullough 
  Cc: www-rdf-interest@w3.org ; David Menendez ; Brian McBride 
  Sent: Friday, November 22, 2002 7:13 AM
  Subject: Re: subclasses (RDF vocabulary definitions)


  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 12:57:04 GMT

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