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Re: Lang: owl:ontolgy (was RE: LANG: syntactic version for imports (and other things))

From: Jeff Heflin <heflin@cse.lehigh.edu>
Date: Mon, 16 Sep 2002 10:25:12 -0400
Message-ID: <3D85E9C8.B37834E4@cse.lehigh.edu>
To: Jim Hendler <hendler@cs.umd.edu>
CC: "Smith, Michael K" <michael.smith@eds.com>, "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>, www-webont-wg@w3.org

Hi Jim,

Actually, this isn't as nice as it might appear. A minor issue is the
redundancy that it introduces in documents. When a user writes an
ontology, why should they have to write the definition and then later
say, oh by the way, this definition is in the ontology that is
represented by the document in which I wrote it? I think we'll have a
hard time explaining this awkwardness to users.

However, a more fundamental issue is that it doesn't really do what we
need it to do. Your approach seems to imply that you can say that a
particular class or property is defined by a particular ontology.
However, in RDF, a class or property can be defined by many ontologies.
The descriptions of these object may be distributed across the Web. In
order to manage reasoning with these things, it is absolutely essential
that we know which descriptions come from which ontologies. In many
cases, we do not want to reason with all the descriptions that everybody
ever said about a class (this is why imports is so important). The only
way to distinguish between what was said in each ontology is to
associate RDF statements (not resources) with the ontology. Thus, each
subclassOf statement, subPropertyOf statement, owl:Restriction
statement, etc. must be associated with the ontology in which it is
stated.

Jeff

Jim Hendler wrote:
> 
> Seems to me today's phone call revealed a problem.  We want to be
> able to define an ontology as a "container" in which a set of
> statements lives.  This doesn't necessarily imply that this container
> is either closed or immutable (this message doesn't want to address
> those issues) but rather to give you a place that makes statements
> about the ontology (heretofore called its metadata) and also to say
> what URIs are in it (not necessarily uniquely).  I've been discussing
> this with a researcher in my lab, Bijan Parsia, and he's come up with
> a solution that is relatively elegant, consistent with the RDF
> approach to the world, and has a precedent in RSS, a widely used
> language.  I think this is similar to what Mike Smith was talking
> about today with using XMLbase, but might be more RDF friendly and
> also a little easier to implement (since everything can stay in the
> graph)
> 
> The idea is that we can simply extend the owl:ontology to define its
> classes in a manner similar to how RSS defines a channel (for those
> who know that) -- that is, we create an owl:ontology statement that
> includes a pointer to the set of URIs which it includes (could be
> just class definitions, could be more).  This would look something
> like this:
> 
> <rdf:RDF  {namespaces} >
> 
> <owl:class rdf:ID="foo">
>    <restriction ... (etc) />
> </owl:class>
> 
> <owl:class rdf:ID="bar">
>    <restriction ... (etc) />
> </owl:class>
> 
> <owl:class rdf:ID="baz">
>    <restriction ... (etc) />
> </owl:class>
> 
> <owl:Ontology rdf:ID="OntologyName">
>   <owl:ontologyDefines rdf:parsetype="collection">
>      <owl:ontologyClass :foo />
>      <owl:ontologyClass :bar />
>      <owl:ontologyClass :baz />
>   </owl:ontologyDefines>
>    <dc:creator rdf:ID="me" />
>       {other metadata}
> </owl:Ontology>
> 
> </rdf:RDF>
> 
> The beauty of this is that I could now handle imports in various ways
> - I could import an entire ontology with an imports statement within
> this
> 
> <owl:Ontology ...>
>    <owl:imports URI2 />
> 
> and extend it
> 
>    <owl:Defines ...>
>      <owl:ontologyClass :notInURI2>
>    </owl:defines>
> ...
> <owl:Ontology>
> 
> I could include classes from other ontologies (Without importing the
> whole thing) by simply including them in my owl:ontologyDefines
> collection
>    <owl:OntologyClass cyc:dog>
> 
> and I get for free some new properties that seem quite desirable - in
> particular, I could create multiple ontologies in a document by
> including pointers to different subsets
> 
> <owl:ontology rdf:ID="Pets">
>    ...
>    <owl:ontologyDefines>
>        ... dog
>        ... cat
>    </owl:ontologyDefines></owl:ontology>
> 
> <owl:ontology rdf:ID="Felines">
>    ...
>    <owl:ontologyDefines>
>        ... lion
>            cat
>            tiger
>    </owl:ontologyDefines></owl:ontology>
> 
> I think that version info could also be handled in here, although
> still working on details.
> 
> I also think this works syntactically whether we put ontologies into
> the domain of discourse or not -- I personally wouldn't prefer to,
> but could go either way.
> 
>   -JH
> p.s. For the RDFS fans, the owl:ontologyDefines would be invertible
> into rdfs:isDefinedBy statements - which is a nice bonus.
> p.p.s. If we really want to get fancy, we could let the
> owl:ontologyDefines statement be any RDF collection, meaning an
> ontology designer could use either a collection, making it closed, or
> a bag, making it open - thus letting the user have some ability to
> control how extensible the solution is.
> 
> --
> Professor James Hendler                           hendler@cs.umd.edu
> Director, Semantic Web and Agent Technologies     301-405-2696
> Maryland Information and Network Dynamics Lab.    301-405-6707 (Fax)
> Univ of Maryland, College Park, MD 20742          240-731-3822 (Cell)
> http://www.cs.umd.edu/users/hendler
Received on Monday, 16 September 2002 10:25:16 GMT

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