- From: Richard H. McCullough <rhm@cdepot.net>
- Date: Fri, 22 Nov 2002 09:57:00 -0800
- To: "Frank Manola" <fmanola@mitre.org>
- Cc: <www-rdf-interest@w3.org>, "David Menendez" <zednenem@psualum.com>, "Brian McBride" <bwm@hplb.hpl.hp.com>
- Message-ID: <002701c29250$8f0f9fc0$bd7ba8c0@rhm8200>
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 UTC