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Re: draft response to #owlref-rdfcore-owl-class-denotation

From: Jonathan Borden <jonathan@openhealth.org>
Date: Thu, 12 Jun 2003 19:31:09 -0400
Message-ID: <019f01c3313a$b754fb90$b6f5d3ce@svhs.local>
To: "Jim Hendler" <hendler@cs.umd.edu>, "pat hayes" <phayes@ihmc.us>
Cc: <www-webont-wg@w3.org>

Pat,

May I summarize your post by saying that owl:Class and rdfs:Class need to be
distinct because the concepts of "Class" in OWL-DL and RDFS are distinct?

If so, what about owl:Class in OWL-DL vs. OWL-Full? Ought not OWL-Full be
defined using rdfs:Class? If so, when using OWL-Full should owl:Class retain
its OWL-DL meaning? Doesn't this 'break' layering? (perhaps I am being
naive?)

It seems to me that the meaning of owl:Class does depend on whether we are
using OWL-DL vs. OWL-Full in which case the meaning of the URIref depends on
the framework we are using ... in which case could not the 'meaning' of
rdfs:Class depend on whether we are using OWL-DL vs. OWL-Full/RDFS?


however,

>...
> And then with these assumptions, we can identify the OWL and RDFS
> universes. This hybrid is called OWL Full. It allows the same
> syntactic freedom as RDFS - it is in fact an RDF semantic extension
> of RDFS - and Peter has proven an ingenious theorem to the effect
> that if one restricts oneself to the OWL-DL syntactic case, then
> being in OWL-DL and being in OWL Full are indistinguishable states,
> as it were, so that OWL-DL is a genuine sublanguage of OWL Full,
> which itself is a genuine RDFS semantic extension.
>
> However, notice that there is a genuine tension here. This Full
> hybrid asserts that the OWL and RDFS universes are identical; but
> they are not, if we understand the OWL terminology according to
> OWL-DL. So OWL Full is constructed so that *either* it must be
> incommensurate with OWL-DL - ie the OWL terminology must have
> different meanings in the two versions of OWL - *or* it is a
> restriction of RDFS to the OWL-DL universe, which makes it
> incommensurate with much of RDFS - for example, many RDFS logical
> truths will be false in OWL Full, under this interpretation. So OWL
> Full either breaks with OWL-DL, or amounts to a grand claim that the
> entire RDFS universe must be understood as conforming to the limited
> OWL-DL 'layered' framework.
>
> It is easy to see that both versions of OWL (DL and Full) could
> safely, each in their own terms, merge the concepts of owl:Class and
> rdfs:Class without actually breaking 'internally': OWL-DL could
> because it is simply unable to express the ways that RDFS classes
> differ from OWL classes - what might be called a 'thought police' way
> of making the vocabularies similar - and OWL Full could simply
> because it is simply asserts that they are identical.  But as I hope
> the above makes clear, this assertion would be troublesome for any
> kind of consistent interaction between OWL-DL and other RDFS
> applications. For example, if OWL-DL were to use the
> rdfs:Class/Resource/rdf:Property terminology while in fact referring
> only to the OWL-DL subsets of these classes, then OWL-DL theorems
> would become sharply false when transcribed into RDFS, and vice
> versa; for example,
>
> _:x rdf:type _:x .
> _:x rdf:type rdfs:Class .
>
> is logically true in RDFS (by rules se1 and se2 from the
> self-membership of rdfs:Class) but would be a logical contradiction
> in OWL-DL if rdfs:Class were identified there with owl:Class. Again,
> many other examples could be given.
>

Understood, but what about 'translating' between OWL-DL and OWL-Full -- same
problem??? e.g.

_:x rdf:type _:x .
_:x rdf:type owl:Class .

logically true in OWL-Full, but contradiction in OWL-DL? (I am assuming that
since owl:Class and rdfs:Class have the same extensions in OWL-Full and
RDFS, that rules se1 and se2 for rdfs:Class apply to owl:Class.)

Jonathan (who doesn't really have a clue about this, but ...)
Received on Thursday, 12 June 2003 19:31:17 GMT

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