RE: rdfs:class and rdfs:resource

This brings up an important issue. I don't believe there is any mechanism in
RDF/RDFS for expressing notions of "time-varying properties" That's not too
say that it cannot be expressed with the current specs, rather I should say
it is not a specified property. At the risk of adding one more thing to the
list of "things which need to be ruled upon" (like "who owns URIs" and
"social meaning"), does this need to be part of the next spec? I'm sure
everyone has their own favorite examples, but just as a starting point (sans
RDF):
	"John Doe is in Paris."

Is this true? To make it unambiguous, do I need to specify a time range? If
I don't know the time range, can I use a relative term such as "during the
time I was in Paris" ?

This is certainly not a new question to logic, but what level of
expressiveness is needed for the SW?

James
	

-----Original Message-----
From: Richard H. McCullough [mailto:rhm@cdepot.net]
Sent: Friday, May 09, 2003 4:12 PM
To: www-rdf-interest@w3.org; Dieter Köhler
Subject: Re: rdfs:class and rdfs:resource



Dieter
I agree with your discussion, but I think your Fido "class" is a bad
example.
Young & old versions of Fido should be considered the same instance
with some time-varying properties.

Dick McCullough
knowledge := man do identify od existent done;
knowledge haspart proposition list;

----- Original Message ----- 
From: "Dieter Köhler" <dieter.koehler@philo.de>
To: <www-rdf-interest@w3.org>
Sent: Friday, May 09, 2003 10:30 AM
Subject: RE: rdfs:class and rdfs:resource


>
> When re-reading my last posting, I got the impression that one sentence
was
> perhaps misleading:
>
> >But the following is, as far as I can see, *not* true:
> ><rdfs:Resource> <rdfs:subClassOf> <rdfs:Class> .
> >
> >In other words: There may exist instances of rdfs:Resources which are not
> >instances of rdfs:Class.  Or again in other words: Not everything must be
> >a class.
>
> The sentence
>    "But the following is, as far as I can see, *not* true:"
> should better read
>    "But the following is, as far as I can see, contingent:"
>
> The following explanation ("in other words ...") can remain
> unchanged.  What I was trying to say was that the statement
>
> <rdfs:Resource> <rdfs:subClassOf> <rdfs:Class> .
>
> does not necessarily follow from the axioms of [RDF Schema].  However, as
> far as I can see, this statement does not contradict the set of RDF Schema
> axioms. [RDF Schema] does not require that all Resources are Classes, but
> also does not state that there indeed exist Resources which are not
Classes.
>
> I also agree with Wolfram that "a (minimal) axiomatization might have a
> certain advantage over the current/previous versions of the RDF/RDFS
> specs", though my chain of reasons is different: Intuitively, I see no
> reason why
>
> <rdfs:Resource> <rdfs:subClassOf> <rdfs:Class> .
>
> should be excluded from RDF/RDFS.  RDF graphs are designed with
> extensibility in mind.  For example, consider the following graph which
> states that Fido is a dog and a dog is an animal:
>
> <foo:Animal> <rdfs:type> <rdfs:Class> .
> <foo:Dog> <rdfs:type> <rdfs:Class> .
> <foo:Dog> <rdfs:subClassOf> <foo:Animal> .
> <foo:Fido> <rdfs:type> <foo:Dog> .
>
> At first glance it seems reasonable to say that Fido is, ontologically
> speaking, an individual, while Dog and Animal are obviously classes.  Now
> consider that we want to add information about the young Fido and the old
> Fido to the above graph.  One way to do so is to add the following
statements:
>
> <foo:Fido> <rdfs:type> <rdfs:Class> .
> <foo:YoungFido> <rdfs:type> <foo:Fido> .
> <foo:OldFido> <rdfs:type> <foo:Fido> .
>
> and also perhaps:
>
> <foo:Fido> <rdfs:subClassOf> <foo:Dog> .  (= every instance of foo:Fido is
> also an instance of foo:Dog)
>
> So every Resource of a graph can be declared being a Class.  That suggests
> that the distinction between Resource and Class is for practical reasons a
> candidate for Okhams razor: The distinction between Resource and Class is
> superfluous and should be dropped in RDF/RDFS.
>
> Dieter Köhler
>
> Institute of Philosophy
> University of Karlsruhe
> Germany
>
>
>

Received on Monday, 12 May 2003 10:17:14 UTC