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Re: rdfs:Class vs. daml:Class ?

From: Dan Connolly <connolly@w3.org>
Date: 29 Mar 2002 09:05:45 -0600
To: Ian Horrocks <horrocks@cs.man.ac.uk>
Cc: David Martin <martin@ai.sri.com>, www-rdf-logic@w3.org
Message-Id: <1017414346.13228.33.camel@dirk>
On Fri, 2002-03-15 at 16:01, Ian Horrocks wrote:
> On March 15, David Martin writes:
[...]
> > > I understand from the Pan and Horrocks paper at
> > > http://img.cs.man.ac.uk/jpan/Zhilin/download/Paper/Pan-Horrocks-rdfsfa-2001.pdf
> > > that there is a layering problem in the RDF/RDF(S) definition that
> > > prevents a clean division between successive metamodel levels. Is the
> > > relationship between rdfs:Class and daml:Class somehow connected to
> > > this?
> 
> More or less. The extension of a DAML+OIL class should be a set of
> individuals (well, strictly a set of objects that are denoted by
> individual names) and not, say, a set of properties, as could be the
> case for an rdfs:Class. Because of the lack of layering in the rdf
> architecture there is no way to enforce this, so daml:Class is just a
> label given to the subset of rdfs:Classes that have the property we
> want.

Ian, please be clear that this is your personal opinion of DAML+OIL,
not the consensus of the group that designed it.

I don't want this property.

I consider the design unfinished, as we agreed 20 Feb 2001:

  RESOLVED: We will release an updated language release
  incorporating the current proposal, acknowledge the outstanding
  issues and concerns, and solicit feedback from the larger
  community.

	-- http://www.daml.org/committee/minutes/2001-02-20.html

I'm quite disappointed that the concerns weren't actually
acknowledged in the spec that was released.

Meanwhile, there are two different formalizations of DAML+OIL:
    *  model-theoretic-semantics.html -
       revised Model-Theoretic Semantics
    * axiomatic-semantics.html - revised Axiomatic Semantics
        (from August 2001) 

	http://www.daml.org/2001/03/daml+oil-index.html

Note the axiomatic semantics doesn't have this bug involving separation
of datatypes from the rest of the universe of discourse.

> Note that in the daml+oil-ex.daml file, daml:Class is used
> extensively. Also note that many of the "meta" properties in the daml
> language definition have daml:Class as a range/domain so that classes
> used in daml ontology will often be implicitly of type daml:Class.
> 
> > >
> > > I suppose all I'm really asking is: when would I use rdfs:Class and when
> > > would I use daml:Class? And if it doesn't matter, why are there two of
> > > them?
> 
> Always use daml:Class.

Or never use it. I don't think it's useful.

> I hope I explained why there are two.

-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Friday, 29 March 2002 10:06:15 GMT

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