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RE: [SKOS] ISSUE-83 semantics of scheme containment properties

From: Alistair Miles <alistair.miles@zoo.ox.ac.uk>
Date: Mon, 28 Jul 2008 14:58:23 +0100
To: "'Antoine Isaac'" <aisaac@few.vu.nl>
Cc: <public-swd-wg@w3.org>
Message-ID: <005901c8f0ba$0027f0e0$0077d2a0$@miles@zoo.ox.ac.uk>

Hi Antoine,

Ah. I've actually implemented the other approach, see <http://www.w3.org/2006/07/SWD/SKOS/reference/master.html#schemes>.

> I agree that the first solution you propose makes the trick from a
> semantic perspective. But I don't like having an extra vocabulary
> element just for this...

In principle I agree with you...

> I had actually written [1] to look a bit like the general entailments
> of
> the SKOS Reference, thinking that we could  just have:
> > ex:cs skos:hasTopConcept ex:c.
> > entails
> > ex:c skos:inScheme ex:cs

This is fine to say in the notes, but we need some way of expressing the underlying condition in the data model. I.e. we need some prose sentence that can be included in the class & property definition statements.  

> Otherwise I think you can indeed introduce a non-named property in an
> OWL axiom, like (hoping I'm not making any mistake...)
> skos:hasTopconcept rdfs:subPropertyOf [ a owl:ObjectProperty;
> owl:inverseOf skos:inScheme .] .

I originally thought of this, but I'm not sure it's ok. Note in particular that the RDF abstract syntax requires all predicates to be named. I.e. you can't have a triple with a blank node in the predicate position. That's why I'm really not sure about using blank predicates in OWL-like axioms.

The only other way I can think of doing it, without a new URI in the SKOS vocabulary, is to start from how you could express the condition as per the rdf/owl full semantics, e.g. 

"for any X, Y, if <X,Y> is in IEXT(I(skos:hasTopConcept)) then <Y,X> is in IEXT(I(skos:inScheme))"

Then try to express this in plain English, e.g.

"if a concept scheme S has top concept C, then C is ..." 

I trailed off there because I can't think of a clear and unambiguous way to say it.

The third alternative of course is simply to state an inference rule, without any underlying semantic conditions. However I'm reluctant to do that, because it would be the first and only time we include an inference rule in the SKOS data model... (has a quick hunt for recent progress on RIF, SWRL, DL-safe rules) ...I guess there are now options for stating inference rules (see e.g. [1]) however knowing very little I fear to open a can of worms.

Hence a new URI and some obvious RDFS and OWL 1 axioms seems like the safest option.

What do you think?



[1] http://code.google.com/p/owl1-1/wiki/SafeRulesOverview

> Again, I would definitively favor one of these two options over
> introducing a new property.
> Cheers,
> Antoine
> [1] http://lists.w3.org/Archives/Public/public-swd-wg/2008May/0068.html
> > Hi Antoine,
> >
> > I'm just trying to figure out how to implement the resolution [1] to
> > issue 83 [2] in the SKOS reference.
> >
> > The most obvious way is to introduce a new property, called something
> > like skos:topConceptInScheme, and introduce two new statements into
> the
> > SKOS data model, that skos:topConceptInScheme is a sub-property of
> > skos:inScheme, and that skos:topConceptInScheme is the inverse of
> > skos:hasTopConcept.
> >
> > Another way would be to avoid introducing any new properties, and to
> > include a new statement in the data model, something like, "the
> inverse
> > of skos:hasTopConcept is a sub-property of skos:inScheme", or "if a
> > scheme has a top concept, then the top concept is in that scheme",
> > or ... ?
> >
> > At the moment I favour the first approach. It has an obvious meaning
> in
> > terms of RDFS/OWL. The second approach has no obvious translation in
> > RDFS/OWL, and is difficult to word.
> >
> > What do you think?
> >
> > Cheers,
> >
> > Al.
> >
> > [1] http://lists.w3.org/Archives/Public/public-swd-
> wg/2008May/0068.html
> > [2] http://www.w3.org/2006/07/SWD/track/issues/83
> >
> >

Alistair Miles
Senior Computing Officer
Image Bioinformatics Research Group
Department of Zoology
The Tinbergen Building
University of Oxford
South Parks Road
United Kingdom
Web: http://purl.org/net/aliman
Email: alistair.miles@zoo.ox.ac.uk
Tel: +44 (0)1865 281993
Received on Monday, 28 July 2008 13:59:01 UTC

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