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Re: LANG: owl:ontology

From: Jeff Heflin <heflin@cse.lehigh.edu>
Date: Thu, 19 Sep 2002 16:48:13 -0400
Message-ID: <3D8A380D.10B7F396@cse.lehigh.edu>
To: pat hayes <phayes@ai.uwf.edu>
CC: Jim Hendler <hendler@cs.umd.edu>, www-webont-wg@w3.org

pat hayes wrote:
> Seems to me that a lot of the discussion about importing has really
> been about what counts as an ontology. Let me suggest that we decide
> this at the syntactic level by saying that an ontology is a set (or
> possibly a bag) of RDF triples. That is not saying that every set of
> RDF triples counts as an ontology, but that the triples-store is the
> appropriate basic syntactic level for defining such things as
> identity of ontologies, mergings of ontologies, entailments between
> ontologies and so on.  This is really just following the RDF spec
> itself.

Sounds okay. 
> Before the howling starts, let me give some arguments for this.
> First, we have decided that the interchange syntax for OWL is
> RDF/XML. But RDF/XML is not a suitable notation for defining
> RDF-meaningful syntactic operations on: that is, RDF-meaningful
> notions of merging, containment (of one set of assertions in another)
> and so on do not correspond to simple syntactic operations on the XML
> surface syntax. So the aforementioned decision about RDF/XML only
> makes sense, seems to me, if we agree that this interchange language
> is in fact being used in the way described by the RDF spec itself, ie
> as a surface/interchange notation for RDF *graphs*.  A possible
> objection to this interpretation has always been that the OWL
> semantics does not agree with the RDF semantics when applied to
> OWL/RDF, so this RDF-centric perspective is not viable when one
> wishes to consider semantically meaningful operations on OWL: I think
> that objection is now refuted, or at least has been demoted from a
> technical objection to an aesthetic one, so should be discounted.
> Which brings me to the second point: treating the RDF graph syntax as
> the basic syntactic level allows us to fairly cleanly define
> OWL-meaningful operations on ontologies, in a uniform way with how
> RDFS-meaningful operations are defined on them. And third, this
> approach preserves the desired interoperability and overall coherence
> between RDF, RDFS and OWL that we all pray for every evening, right?
> On this view, then, having [imports B] included in A would be saying
> (semantically) that if if the graph-merge of A and B entails C then A
> entails C, or (syntactically) that A should be considered to have B
> graph-merged into it; where 'A' and 'B' throughout are taken to refer
> to whatever collections of RDF triples the syntactic form being used
> maps into. In the case of OWL/RDF/XML, that would an OWL closure,
> which might be quite a large set: OK, but that's OWL life.
> Implemeters of course can choose to be clever in various ways.

In my summary [1], this sounds like alternative c to Question 1 of Issue
5.6. Sorry, I didn't get around to reading this message until I wrote
that summary, or else I would have referenced it.

I could probably live with this, but only if we end up deciding that the
RDF graph is the basis for the OWL semantics. I think defining the
semantics from the RDF graph makes things more complicated than they
have to be, but can't come up with any strong reasons against it. I'll
leave that to Peter and Ian, if they are so inclined.

> Pat
> --
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Received on Thursday, 19 September 2002 16:48:17 UTC

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