W3C home > Mailing lists > Public > public-esw-thes@w3.org > September 2004

Re: [Proposal][SKOS-Core] skos:denotes

From: Dave Reynolds <der@hplb.hpl.hp.com>
Date: Thu, 30 Sep 2004 18:37:49 +0100
Message-ID: <415C446D.6040808@hplb.hpl.hp.com>
To: "Matthews, BM (Brian) " <B.M.Matthews@rl.ac.uk>
Cc: "'public-esw-thes@w3.org'" <public-esw-thes@w3.org>

Matthews, BM (Brian) wrote:

> As I interpret this,  this gives the best semantics I know of for 
> Thesaurus concepts - a concept's denotation is "the set of resources 
> which are classified under that concept" (my words).  This is quite 
> different from the intended use in Ontologies, where instances are 
> "supposed" to stand for "real-world" things (with suitable philosophical 
> quotation marks).

I agree with that summary of the semantics of Thesaurus concepts but I'm 
not so sure ontologies are that different. Sure in philosophical terms 
ontologies are more than that, as you say, but in practical RDFS and OWL 
terms a class is just a set of instances and an instance is just a 
"resource". It so happens that OWL gives you some machinery for identifying 
the class of a resource by its properties, and RDFS gives you less, but the 
difference between those and your semantics for Thesaurus concepts is just 
a matter of expressivity rather than of fundamental nature.

Personally I find this article nicely captures this view that they are just 
a continuum with different expressivity and degree of formality:
http://www.metamodel.com/article.php?story=20030115211223271

> So I think that the word "denotes" to connect a thesaurus-theoretic and
> a ontology-theoretic point of view is dangerous - as in logic
> and mathematics this usually signifies semantics - we are not (should
> not) be saying that the class provides a semantics for the concept.

Agreed.

> An alternative term then?  skos:classifierFor is perhaps most precise,
> though a bit awkward.  But I prefer it to the alternatives we have
> seen so far which imply some kind of semantic relationship.

To me that also implies a semantic relationship but maybe that's just me.

> Nikki says:
> 
>>Or is this debate really about the fact that we want to stick some 
>>machinery capable of SKOS<->OWL stuff in SKOS-Core right now, so that 
>>SKOS-Core stands in its own right allowing us to tackle SKOS-Mapping 
>>separately?
> 
> 
> As far as I see - yes!  The use of this property is to do the modelling
> task of relating SKOS and OWL - and SKOS-mapping should be separate.

To me there's no particular difference between saying that two SKOS 
Concepts are trying to model the same "real world" thing and saying that a 
SKOS Concept and an OWL Class are trying to model the same "real world" 
thing. So I'm with Nikki, it seems odd putting it in the core rather than 
in mapping.

> To turn to the specifics of the proposal (to start a new controversy),
> does it make sense (particularly when taking a point of view that
> we are providing a classifier for an RDF resource) for this property
> to be a functional property?  This would mean if two resources have the
> same classifier, they can be identified.  This may not make sense.

My vote would be "no".

For example, you might have a SKOS Thesaurus concept "my:Person" an RDF 
Class foaf:Person and an RDF Class drc:Person. They are all trying to model 
the same real world notion but in different ways (e.g. drc:Person might 
have cardinality restrictions on properties that foaf:Person has nothing to 
do with). As I understand it, the point of this property is to be able to 
say "my:Person and foaf:Person are both attempts to model the same thing" 
without carrying any semantics such as cardinality restrictions.

It would be reasonable to also want to say "my:Person and drc:Person are 
both attempts to model the same thing" without that implying that 
drc:Person = foaf:Person (with all that would entail from the formal 
semantics of the foaf and drc schemas).

Cheers,
Dave
Received on Thursday, 30 September 2004 17:37:58 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Monday, 7 December 2009 10:38:52 GMT