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Re: DAML: restricting number of elements in a list

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Mon, 11 Feb 2002 11:00:22 +0000
Message-ID: <15463.42054.167114.214568@galahad.cs.man.ac.uk>
To: Ken Baclawski <kenb@ccs.neu.edu>
Cc: Steven Gollery <sgollery@cadrc.calpoly.edu>, www-rdf-logic@w3.org
On February 11, Ken Baclawski writes:
> On Sat, 9 Feb 2002, Ian Horrocks wrote:
> 
> > On February 7, Ken Baclawski writes:
> > > The daml:item property relates a list to each of its elements.  One can
> > > impose a daml:minCardinality restriction on the daml:item property to
> > > ensure that the number of vertices in a polygon is at least 3. 
> > > 
> > > Ken Baclawski
> > > Ken@Baclawski.com
> > > UBOT Project
> > 
> > I am afraid that this is a common misconception. You can write such a
> > thing, but if you read the language specification you will find that
> > daml+oil does not provide any semantics for it, so it does not have
> > the effect that you desire (in fact, from the point of view of
> > daml+oil, it has no effect whatsoever). 
> 
> You are correct that the intention of daml:collection is to be unordered,
> but the axiomatic semantics specifies that DAML lists do have an order,
> via the daml:first and daml:rest properties.  Furthermore, the axiomatic
> semantics specifies that daml:item relates a list to each item in the list
> (item-axiom-2).  Which one specifies the semantics of DAML+OIL:  the
> axiomatic semantics (written in KIF) or the language specification
> (written in English prose)? 

It isn't a question of whether lists are ordered or not (although as
you point out lists are treated as sets DAML+OIL), it is the fact the
the list construction forms part of the syntax specification of the
language. If you check he model theoretic semantics (the definitive
specification of the meaning of DAML+OIL), you will see how this
works. 

The confusion is caused by the fact that RDF does not separate
modelling layers, so the "meta-model" (i.e., the specification of the
syntax of the language) is mixed up with the model (an ontology
defined using the language). 

Ian


> 
> Ken Baclawski
> Ken@Baclawski.com
> UBOT Project
> 
Received on Monday, 11 February 2002 05:54:24 GMT

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