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Re: draft partitioning of the issues

From: pat hayes <phayes@ai.uwf.edu>
Date: Tue, 26 Jun 2001 13:44:11 -0500
Message-Id: <v0421010db75e875d3263@[205.160.76.189]>
To: Art Barstow <barstow@w3.org>
Cc: w3c-rdfcore-wg@w3.org
>On Tue, Jun 26, 2001 at 02:33:54PM +0100, Brian McBride wrote:
> >
> > Aaron Swartz wrote:
> >
> > > > Is there any doubt that as far as m&s is concerned:
> > > >
> > > >   o literals are not allowed as subjects
> > > >   o literals are not resources
> > >
> > > I do not see either of these stated in the spec. M&S says:
> > >
> > >          pred is a property (member of Properties), sub is a resource
> > >         (member of Resources), and obj is either a resource or a
> > >         literal (member of Literals).
> > >
> > > but it never says that literals and resources are disjoint in
> > > any normative portion of the document (to my knowledge, after a
> > > quick search).
> >
> > Yes, I think you are right that it does not state explicitly that they
> > are disjoint.  In reading the spec I ascribe some information to the
> > fact that m&s calls out that an object can be either a resource or a
> > literal and says only that subject is a member of resources.  Whilst this
> > may not be a mathematically precise statement that resources and
> > literals are disjoint, it seems pretty clear that it was the intent
> > that they are and that subjects may not therefore be literals.
>
>Is anyone aware of any implementations that reflect an
>interpretation of the spec where the set Resources and
>the set Literals per:
>
> http://www.w3.org/TR/REC-rdf-syntax/#model
>
>are NOT disjoint?

For what its worth, a related issue (whether or not to insist that 
literals were disjoint from 'abstract values') arose on the DAML 
c'ttee and was hotly debated. Eventually, the description logicians 
won the day by claiming that to not keep them apart would render many 
DL inference efficiencies hopelessly broken. The problem seems to 
arise when one can have class definitions that depend on the values 
of literal expressions in any but a few carefully controlled ways (eg 
by cardinality constrainsts) since that could lead to the inference 
process needing to solve arbitrarily difficult equations over 
semantic spaces corresponding to literals.

Just a data point that may be relevant.

Pat

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Received on Tuesday, 26 June 2001 14:44:13 EDT

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