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Re: REQDOC: ontologies as resources

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Thu, 14 Feb 2002 17:02:36 -0500
To: danbri@w3.org
Cc: www-webont-wg@w3.org
Message-Id: <20020214170236N.pfps@research.bell-labs.com>
From: Dan Brickley <danbri@w3.org>
Subject: Re: REQDOC: ontologies as resources
Date: Thu, 14 Feb 2002 15:58:54 -0500 (EST)


> On Thu, 14 Feb 2002, Peter F. Patel-Schneider wrote:
> > In a message expressing my concerns with the requirements document, I
> > argued that it is premature to require that ontologies be resources, at
> > least if by resource, we mean an RDF resource, i.e., elements of the domain
> > of discourse that can be used just like any other element of the domain of
> > discourse.
> I think this is the crux of the WebOnt/RDFS layering dispute. While folk
> have often focussed on the "RDF schema says that class is a class" aspect,
> this spin on the issue gets us closer.


> But RDF
> (not just RDFS) does establish the convention that
> 'http://example.com/myvocab#livesWith' is in the domain of discourse, and
> as such open to further description by arbitrary parties using arbitrary
> vocabularies.


> Having properties and classes in the domain
> of discourse meant that the RDFS 1.0 WG didn't have to take upon
> themselves the task of enumerating all the useful kinds of things one
> might say about classes and properties. Having watched various schema
> efforts come and go, I strongly suspect this WG will find this an
> attractive feature.


This is all fine and good, except that RDF and RDFS together place a rather
severe limit in the sorts of things that can be said about classes and
properties.  RDF requires that classes and properties (in particular
rdf:type) live in the domain of discourse, and thus that the theory of
classes and properties can be referred to by any theory of classes and
properties.  RDFS requires that this theory incorporate self-reference.
(Actually what RDFS requires is rather more complex than this, but
self-reference is sufficient to get to the problems below.)

It doesn't take much more to allow semantic paradoxes.  In essence all that
is missing is some notion of pervasive classes (provided by DAML+OIL
Restrictions) and some notion of complement (provided by a number of
DAML+OIL constructs).  You then have versions of Russel's paradox.
(The easiest version to construct is the restriction whose instances are
not related to the restriction by rdf:type.)

So in the interests of generality RDF and RDFS have essentially disallowed
most logical constructs.


PS:  What does this have to do with ontologies being resources?  Well,
     nothing directly, but Dan Brickley's comments had to do with classes
     and properties being resources.
Received on Thursday, 14 February 2002 17:03:49 UTC

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