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Re: ISSUE: Classes as instances

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Tue, 16 Jul 2002 10:32:13 -0400
To: schreiber@swi.psy.uva.nl
Cc: www-webont-wg@w3.org
Message-Id: <20020716103213Z.pfps@research.bell-labs.com>

From: Guus Schreiber <schreiber@swi.psy.uva.nl>
Subject: Re: ISSUE: Classes as instances
Date: Fri, 12 Jul 2002 15:12:46 +0200

[...]

> Encl. is a detailed example of Raphael's scenario 1.

[...]

> One disadvantage of the above representation is that the WordNet
> hyponym hierarchy is now "hidden" in the hyponymOf triples. 

Why are you saying that the hyponym hierarchy is hidden?  Do you mean that
it can't be found?  Surely not.  Do you mean that some aspects of the
hyponym hierarchy are not captured in this RDFS representation?  Probably.
Well, so what?  Representation is at least partly about determining what to
capture and what not to capture.

> One could
> therefore argue that this representation is wrong. 

Please explain.  What is ``wrong'' about this representation?

> However, if the
> semantic web really becomes a reality, different representation
> choices will be a fact of life. So, we looked at a way of
> defining our interpretation of "WordNet as a class hierarchy" as an
> add-on RDF Schema. 

> It turned out that with two definitions we could
> solve this problem:
> 
>   wn:LexicalConcept rdfs:subClassOf rdfs:Class
>   wn:hyponymOf rdfs:subPropertyOf rdfs:subClassOf
> 
> The first definition makes it possible to treat a synset as a class,
> which is a requirement to able to treat hyponymOf as a sort of
> subclass relation (i.e. the second definition).

Well, sure, *if* you want to treat hyponymOf ``as a sort of subclass
relation''.  However, why would you want to do this?  What do you achieve
by this?  

Perhaps the only reason for making hyponymOf a subclass relationship
derives from limitations in RDFS.   For example, would it not be better to
make hyponymOf a transitive relation, as is possible in OWL?  

[...]

> With these four definitions the RDF parser and browser used by our semantic
> annotation & search tool is perfectly happy. 

Why would the ``RDF parser and browser'' be unhappy without these
four *triples*?  Are you saying that without these four triples your RDF
parser and browser cannot read in the documents?  If so, why?

> The tool uses the
> hierarchy in several ways. e.g.:
> - for making it easy for users to understand the intended
>   meaning of a term (e.g. "Venus" as a subclass of "Roman deity" or as a
>   subclass of "planet"). This is used in annotation/search term
>   disambiguation.
> - for query generalization/specialization.
> [See [3] for more info]

Why does the tool depend on subclass?  Would it not be just as easy
to use a transitive relationship?

> Although it first seemed like a hack, on second thought this might
> actually be a decent way to do this kind of ontology/representation
> mapping. Again, in the semantic web we will have to live with
> representation choices made by others.

Agreed, but this does not imply to me that we have to allow classes as
instances.

> 3. Implications for OWL
> 
> OWL should not disallow this type of mapping.

I don't think that you have provided convincing evidence of this
conclusion.

> Comments/suggestions are very welcome,
> 
> Guus
> 
> [1] http://www.semanticweb.org/library#wordnet
> [2] http://www.swi.psy.uva.nl/usr/Schreiber/schema/wnclass.rdfs
> [3] http://www.swi.psy.uva.nl/usr/Schreiber/papers/Schreiber01a.pdf

Peter F. Patel-Schneider
Bell Labs Research
Received on Tuesday, 16 July 2002 10:32:28 GMT

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