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Re: rdfs:Class vs. daml:Class ?

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Sun, 7 Apr 2002 13:02:45 +0100
Message-ID: <15536.13669.913724.677939@oaklands.demon.co.uk>
To: Dan Connolly <connolly@w3.org>
Cc: David Martin <martin@ai.sri.com>, www-rdf-logic@w3.org
On March 29, Dan Connolly writes:
> 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.

It isn't a bug, its a feature. Without the separation, the scope of
the semantics needs to include all the XML Schema datatypes and
built-in predicates. I don't think we want to go there (and I am sure
that the axiomatic semantics doesn't do so).

Ian




> 
> > 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 Sunday, 7 April 2002 08:05:14 GMT

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