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Re: subclasses (RDF vocabulary definitions)

From: Richard H. McCullough <rhm@cdepot.net>
Date: Fri, 22 Nov 2002 12:17:35 -0800
Message-ID: <000c01c29264$327d42d0$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>
I like to talk about reality.
Man subsumes all men, past, present and future.
Ditto for Animal.
if  Animal  rdfs:sameAs  Man
it means that Animal and Man are identical,
that Man is an alias of Animal and vice versa.

Now if you're going to tell me that RDFS can't describe reality,
then I'm not interested in RDFS.
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 11:56 AM
  Subject: Re: subclasses (RDF vocabulary definitions)

  Richard H. McCullough wrote:

  > 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

  I'll try again:

  I know that's what you're explicitly talking about;  but "sameAs" is 
  just a piece of syntax unless we can also talk about what "sameAs" 
  *means*.  And it seems to me we have to talk what "sameAs" means by 
  looking at the logical consequences of stating it.  I'm saying that if 
  you say

  Man "sameAs" Animal, you are saying

  if aa is a Man, then aa is an Animal



  if aa is an Animal, then aa is a Man.

  Putting that in RDF entailment rule form (which is what I did earlier in 
  this thread for the entailments allowed by rdfs:subClassOf), Man 
  "sameAs" Animal would mean

  Man sameAs Animal
  aaa rdf:type Man


  aaa rdf:type Animal


  Man sameAs Animal
  aaa rdf:type Animal


  aaa rdf:type Man

  On the one hand, I take it you will agree that, at any point in time, it 
  might very well be the case that the set of resources (the set of things 
  with URIs) that are also described as being of class Animal (having 
  rdf:type properties with class Animal as the value) might very well be 
  the same as the set of resources described as being of class Man (having 
  rdf:type properties with class Man as the value), even if you've stated 
  that Man is a proper subset of Animal?  The two sets being the same is 
  an "accident" of sorts:  I've just not described any wolves or tigers 
  yet.  But this situation surely must be allowed to exist.  On the other 
  hand, if I have the "sameAs" *definition*, this is the statement of a 
  *rule* I should be able to make inferences from:  I should be able to 
  infer from the fact that something is an Animal that it necessarily must 
  be a Man, and vice-versa.

  Now, Man rdfs:subClassOf Animal certainly allows for the situation above 
  to exist where the sets of resources you've so-far identified as Man and 
  Animal happen to be the same.  However, my point is that, if 
  rdfs:subClassOf, *as a definition*, did not rule out the possibility 
  that the two class had to be the same, it would allow both the "sameAs" 

  Man rdfs:subClassOf Animal
  aaa rdf:type Man


  aaa rdf:type Animal


  Man rdfs:subClassOf Animal
  aaa rdf:type Animal


  aaa rdf:type Man

  And my point was that RDF does not license this second entailment.


  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 15:17:37 UTC

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