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Re: rdfs:class and rdfs:resource

From: Francesco CannistrÓ <fracan@inwind.it>
Date: Fri, 9 May 2003 18:40:21 +0200
Message-ID: <025d01c31649$af8e7b40$8d951d97@Matrix>
To: "Dr. Wolfram Conen" <conen@gmx.de>, <www-rdf-interest@w3.org>

Wolfram,

your latest comments are excellent and perfectly "in topic" with my taste.
But I want to let you note what follows:
1) your axiom (I) is already assumed (at least implicitly) within the RDF
spec;
2) RDF Schema is an application of RDF [necessarily part of this???] and,
therefore, it must imports all RDF's assumptions.
In conclusion:
3) the concept of "Resource" is not (neither could be) introduced by RDF
Schema,
4) RDF Schema just captures this concept giving to it a name and then, once
introduced a set of concepts (among which that one of rdfs:Class) by
leveraging the innate concept of "Resource" as suggested by RDF, projects
the innate concept of "Resource" within the conceptual world it created
(assertig that rdfs:Resource is of type rdfs:Class).

do you agree with me?

Francesco

----- Original Message -----
From: "Dr. Wolfram Conen" <conen@gmx.de>
To: <www-rdf-interest@w3.org>
Sent: Friday, May 09, 2003 4:32 PM
Subject: Re: rdfs:class and rdfs:resource


>
> Dieter,
>
> in a sense, a (minimal) axiomatization might have a certain advantage over
> the current/previous versions of the RDF/RDFS specs:  it might be easier
to
> "check" if our intuition of what RDF/RDFS should be (in its intended
> function as a "fundament" for the further development of the Semantic Web)
> coincides with what it currently "is" (by interpreting the specs).
>
> For example, a small concern might be the following:
> (I) We talk about resources
> (II) Every resource is the subject of (at least) one statement with
rdf:type
> as its predicate (being imprecise by using rdf:type as a surrogate for the
> resource that is the map of rdf:type in an interpretation)
> (III) Now, given such a (triplized) structure of resources/type-relations,
> we may want to "capture" the concept "class" by saying that every
resources
> that is used as an object in a statement with a predicate rdf:type is such
a
> class.
>
> Ok, I could probably agree to this - now, we can speak of classes (when
> talking about our universe of resources/relations) and map this
unambigously
> to our intial graph (with resources and relation among resources)
(requiring
> the use of projection).
> What we could also immediately introduce is the concept
> "resource-which-is-not-a-class".
>
> Now, in RDFS, this is a bit more tricky: what is a class intended to be
> (which "idea/notion/concept" does it capture)? ("class": the concept
> intended to be represented by rdfs:Class).
> -- we again talk about resources
> -- Also, every resource is the subject of (at least) one statement with
> rdf:type as its predicate (apply the closure rules of the MT)
> Ok. Hm, so is the (extensional) class-concept outlined above applicable?
> Almost...(RDFS wants to help us ;-) - it seems as if the "name"
rdfs:Class"
> is intended to be mapped to a resource which captures the concept "class"
in
> the interpretation of an RDFS closure graph. To explain: every "resource
> name" that is mapped to a resource (in the interpretation) that is a class
> in the above sense (III), will also occur on subject position in a
statement
> with rdf:type as a predicate and rdfs:Class as an object.
>
> Ok, fine. But...we can also use such statements to type resources with
empty
> extension as being classes...what's the point of doing this? In the end,
> what intuition/idea/notion is the concept "class" in RDFS intended to
> capture? And, more importantly, what would be a "useful" intuition? (or,
> even more interesting, do we need a prescribed notion for classes at all?
> Couldn't we offer a mechanism (LBase+Syntax?) which would allow the schema
> "designer" to capture his intentions "on the fly" (by resorting to the
usual
> concepts of First Order Predicate Calculus, for example - capturing (III)
> above is extremely simple)...ok, this is an old discussion...I just
intended
> to say that stepping back from the spec and thinking about what should be
in
> them might be interesting sometimes (I know, the core WG worked very hard
on
> improving things, but they set out their endeavour with the premise to
> evolve...sometimes revolutions ahd their use too ;-)
>
> Sorry if this is too much "off topic".
>     All the best,
>         Wolfram
>
>
>
>
> ----- Original Message -----
> From: "Dieter K÷hler" <dieter.koehler@philo.de>
> To: <www-rdf-interest@w3.org>
> Sent: Thursday, May 08, 2003 12:07 PM
> Subject: RE: rdfs:class and rdfs:resource
>
>
> >
> >
> > >Thanks to everyone on attempting to clarify this rdfs:class and
> > >rdfs:resource issue. But, either I'm missing something, or these
> > >explanations are. Specifically, I need to see a careful description of
> the
> > >classes and *instances* involved.
> >
> > Perhaps things get clearer by concentrating on the essential statements
> > about rdfs:Resource and rdfs:Class in the [RDF Schema] specification. In
> > terms of the calculus specified in [RDF Schema] the following RDF
> > statements are true (the numbers in brackets refer to the paragraph in
the
> > specification):
> >
> > <rdfs:Resource> <rdf:type> <rdfs:Class> . (2.1)
> > <rdfs:Class> <rdf:type> <rdfs:Class> . (2.2)
> > <rdfs:Class> <rdfs:subClassOf> <rdfs:Resource> . (2.1)
> > <rdfs:Resource> <rdf:type> <rdfs:Resource> . (Because all instances of
> > rdfs:Class are instances of rdfs:Resource, and rdfs:Resource is an
> instance
> > of rdfs:Class (2.1 and 3.4).)
> >
> > 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.
> >
> > Footnote: I think it is unnecessary to talk *here* about
> > meta-languages:  One may or may not on a meta-level require that all
> > resources are classes (or in terms of scholastic philosophy: that all
> > individuals are concepts).  And the question what comes first, resources
> or
> > classes, might be interesting if we try to form a hierarchy of different
> > calculuses based on each other, but the simple answer for [RDF Schema]
is
> > that it has no hierarchical structure and should be considered as a
> > whole.  Of course one could try to reduce the number of its axioms while
> > the possible conclusions remain the same, but because of the
> > dissimilarities of rdfs:Resource and rdfs:Class neither can simply be
> > reduced to the other.
> >
> > Dieter K÷hler
> >
> > Institute of Philosophy
> > University of Karlsruhe
> > Germany
> >
> >
>
> ----- Original Message -----
> From: "Dieter K÷hler" <dieter.koehler@philo.de>
> To: <www-rdf-interest@w3.org>
> Sent: Thursday, May 08, 2003 12:07 PM
> Subject: RE: rdfs:class and rdfs:resource
>
>
> >
> >
> > >Thanks to everyone on attempting to clarify this rdfs:class and
> > >rdfs:resource issue. But, either I'm missing something, or these
> > >explanations are. Specifically, I need to see a careful description of
> the
> > >classes and *instances* involved.
> >
> > Perhaps things get clearer by concentrating on the essential statements
> > about rdfs:Resource and rdfs:Class in the [RDF Schema] specification. In
> > terms of the calculus specified in [RDF Schema] the following RDF
> > statements are true (the numbers in brackets refer to the paragraph in
the
> > specification):
> >
> > <rdfs:Resource> <rdf:type> <rdfs:Class> . (2.1)
> > <rdfs:Class> <rdf:type> <rdfs:Class> . (2.2)
> > <rdfs:Class> <rdfs:subClassOf> <rdfs:Resource> . (2.1)
> > <rdfs:Resource> <rdf:type> <rdfs:Resource> . (Because all instances of
> > rdfs:Class are instances of rdfs:Resource, and rdfs:Resource is an
> instance
> > of rdfs:Class (2.1 and 3.4).)
> >
> > 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.
> >
> > Footnote: I think it is unnecessary to talk *here* about
> > meta-languages:  One may or may not on a meta-level require that all
> > resources are classes (or in terms of scholastic philosophy: that all
> > individuals are concepts).  And the question what comes first, resources
> or
> > classes, might be interesting if we try to form a hierarchy of different
> > calculuses based on each other, but the simple answer for [RDF Schema]
is
> > that it has no hierarchical structure and should be considered as a
> > whole.  Of course one could try to reduce the number of its axioms while
> > the possible conclusions remain the same, but because of the
> > dissimilarities of rdfs:Resource and rdfs:Class neither can simply be
> > reduced to the other.
> >
> > Dieter K÷hler
> >
> > Institute of Philosophy
> > University of Karlsruhe
> > Germany
> >
> >
>
Received on Friday, 9 May 2003 12:40:36 GMT

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