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

From: Dan Brickley <danbri@w3.org>
Date: Tue, 17 Sep 2002 20:45:42 -0400 (EDT)
To: pat hayes <phayes@ai.uwf.edu>
cc: Jeff Heflin <heflin@cse.lehigh.edu>, <www-webont-wg@w3.org>
Message-ID: <Pine.LNX.4.30.0209172030310.8610-100000@tux.w3.org>

On Tue, 17 Sep 2002, pat hayes wrote:

>
> Jeff, thanks for stating this so succinctly so that I can ask you why
> you believe these things. I simply do not follow your reasoning.
>
> >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.
>
> OK so far, and I agree...
>
> >In
> >order to manage reasoning with these things, it is absolutely essential
> >that we know which descriptions come from which ontologies.
>
> WHY??? Why do I need to know where the information came from? I can
> see that for some 'advanced' purposes - for example, suppose I don't
> trust all my sources and I want to keep track of what follows from
> what authorities, or I expect to find inconsistencies and want to do
> truth-maintenance - that such meta-information might be important,
> but the basic inferential model of RDF and DAML+OIL and OWL is surely
> that in which I have many sources of information, and I draw
> conclusions from them about the things they refer to. For this I
> don't need to know where the information *comes from*.

I agree with both of you. Often times, when dealing with an aggregate of
scattered information from the Web, you'll want to be keeping track of who
said (and digitally signed, etc) what. But Ontologies are just one
particularly interesting instance of this broad need. All the RDF/XML I
harvest and store gets tagged with more information than is present in the
simple RDF graphs those documents encode. I don't bother trying to use RDF
reification or any standards based approach; this, for now, is a private
business between me and my database system. We could use RDF's reification
vocab if we really wanted to try to do such things over the top of simple
RDF graphs, but it's pretty painful. So in the absence of an easy way to
do this 'inside' RDF 1.0, my preference is to document this as evidence
for provenance-tracking facilities in some richer Web KR language (RDF 2,
whatever). Building something special-purpose just for keeping track of
claims that were made in/about ontologies seems an expensive
undertaking...

> >In many
> >cases, we do not want to reason with all the descriptions that everybody
> >ever said about a class

or about a person, a company, a web page, an mp3...

>
> Of course not....

(nods)

> >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.
>
> WHY?? What purpose does this serve for a basic, vanilla RDF/OWL
> reasoner? What conclusion can it draw (or not draw) with these tags
> present, that it could not (or could) draw if they were absent? What
> entailments do they effect? Seems to me, the only possible answer is,
> none whatsoever.

Yup. The ability for RDF/OWL tools (databases, reasoners, query languages)
to deal interestingly with the who-said-what is much anticipated, but
that's not something the core RDF machinery provides much support for.
It's a value added thing; if we see a lot of support for it in tools, and
lots of use cases (like Ontology provenance) that might be good evidence
for getting more built in support in some hypothetical future version of
RDF.

> Pat

Dan


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Received on Tuesday, 17 September 2002 20:45:44 GMT

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