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Re: SEM: Light review of semantics document

From: Jonathan Borden <jonathan@openhealth.org>
Date: Sun, 10 Nov 2002 11:01:01 -0500
Message-ID: <004201c288d2$5e5fedd0$7c674544@ne.mediaone.net>
To: "Christopher Welty" <welty@us.ibm.com>, <www-webont-wg@w3.org>, "Jim Hendler" <hendler@cs.umd.edu>

Jim Hendler wrote:
>
> At 3:00 PM -0500 11/8/02, Christopher Welty wrote:
> >I have to agree with Pat here, guys.  The meaning of an "owl:ontology"
tag
> >inside an RDF document is simply that the document contains OWL syntax,
> >not some hard to pin down notion of a separation between definitions and
> >data.
> >
>
> Chris/Pat - I think you guys misunderstood me - I believe that all of
> these things are OWL documents, but I'm concerned with a small matter
> of usage.  The way I see it, there are documents which are clearly
> owl ontologies because they define terms and properties and the like.
> There are also owl documents that only use those terms and, in fact,
> there is no reason that there will be any trace of any OWL vocabulary
> in those documents.  For example, if Chris defines an ontology about
> people, I could have a document which contains only the following:


I agree. Especially if you consider OWL (full) as an extension of RDFS, you
are going to find a whole host of problems trying to draw a sharp line in
the sand between RDF data and OWL ontologies.

Indeed once an OWL 'document' with an owl:Ontology triple has been parsed
into a triple store, the connection between the owl:Ontology triple and the
rest of the triples has been effectively lost -- I', and others, have
suggested that RDF needs some notion of 'context' to fix this but that is
the simple fact of RDF. You pick your cake, now eat it.


>
> Namespace definitions to RDF and to Chris' document
>
> <rdf:RDF>
>    <chris:person rdf:id="Hendler" />
> </rdf:RDF>

Well what if *I* say something like:

chris:person owl:subClassOf owl:Class .

elsewhere, and suppose I believe this :-), now your supposedly perfect RDF
document *does* use OWL terms...


>
> by the definition "uses owl terminology" this is NOT and owl
> document.  By the definition "uses terms from an owl ontology" this
> is an Owl document.
>
> So I am asking for terminology that would
>     i. let me differentiate this document from an arbitrary RDF
> document (and Pat, please note I wasn't being anti-logical, but it
> seems to me we don't need this distinction to have a logical meaning
> in the formal sense -- I'm simply looking for a common term to mean
> RDF documents that are expecting to be linked to owl ontologies) --
> Jeff called this a data document, which Pat didn't like.

Given OWL Full and the spirit of RDF, where anyone *might* say anything
about anything at anytime, you just cannot draw a sharp line between the
two. At most you can say that it is unknown if an RDF 'document' is an OWL
'document'

>    ii. lets me differentiate this kind of document from an owl
> document which does contain class and property definitions and
> restrictions.  I DO KNOW what to call the ones that have that (an
> ontology), but not what to call the other ones.
>
>   I believe strongly that this is not a critical issue of language
> design, it's simply a suggestion we develop consistent terms so we
> get our message out.
> Technically, it is clear to me the document above is an RDF document
> - it would use the RDF Model Theory and all would be happy.  But
> colloquially, we need to be able to discuss these documents with a
> term that people in the outside world can understand.
>
>   In class, I refer to these as "Owl data sets" and the students get
> it, I'd be happy with that term.
>
> So, I ask Pat/Chris and anyone else inclined to help out:
>
>   what name shall we use for documents that are in the class with the
> following properties:
>
> Document a rdf:RDF document AND
> Document uses terms from a owl ontology document AND
> Document NOT a owl ontology document.
>
> IMHO, If we call such a document an "ontology," we're going to
> confuse  a lot of people.

This motivates me to write up the media-type document:

The publisher of a document can label one as
application/rdf+xml

and another as
application/owl+xml

by definition, *any* RDF document labelled as application/owl+xml is part of
an ontology.
by definition *any* RDF document labelled as application/rdf+xml is RDF and
*might be* part of an ontology

Good luck folks, but this is an artifact of RDF and OWL Full. Of course I am
willing to listen to a good argument to the contrary its just that I can't
imagine some plain ol' RDF being 'converted' into OWL at some later time, or
on discovery of some other document e.g. suppose:

http://example.org/RDF/data.rdf
<rdf:RDF>
    <foo:bar rdf:ID="baz"/>
</rdf:RDF>

and then

http://example.org/OWL/ontology-decls:
<rdf:RDF>
    <owl:Ontology rdf:about="http://example.org/RDF/data.rdf">
        ...
    </owl:Ontology>
    <owl:Class rdf:about="http://example.org/RDF/data.rdf#baz">
        <owl:subClassOf rdf:resource="...#bop"/>
    </owl:Class>
</rdf:RDF>

Jonathan
Received on Sunday, 10 November 2002 11:20:39 GMT

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