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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 16:31:41 +0100
To: "'Antoine Isaac'" <aisaac@few.vu.nl>
Cc: <public-swd-wg@w3.org>
Message-ID: <000301c8f0c7$08d1e270$1a75a750$@miles@zoo.ox.ac.uk>

Hi Antoine,

Comments inline...

> >> 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.
> >
> 
> I'm sorry but again I'm not sure to understand. In the code above all
> my
> predicates are named.
> I guess a proper OWL reasoner reading this should not ouput inferred
> statements corresponding to the "hidden" property (because indeed you
> cannot have a blank node as a predicate in a graph) but would still use
> that in its internal processes to infer the statements with the
> inScheme
> that wwe're interested in.
> But that's at the level of how the OWL reasoner handles this, I guess
> we
> can rely on that... (but I admit I'm far from an expert on that)

I *think* the problem is that the condition you state above, under the OWL Full semantics, would entail triples that have blank nodes in the predicate position.

So e.g. stated another way

skos:hasTopConcept rdfs:subPropertyOf _:p .
<X> skos:hasTopConcept <Y> .

might entail 

<X> _:p <Y> .

which is not legal RDF.

Similarly, 

_:p owl:inverseOf skos:inScheme .
<X> skos:inScheme <Y> .

might entail 

<Y> _:p <X> .

which again is not legal RDF.

Let's just do this the obvious way, and give our mystery property a name. Why not? What's the down-side?

> 
> > 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.
> >
> 
> But wouldn't that also fail your 'we have to put in it in the OWL
> ontology' stance?
> Otherwise I'd be perfectly happy with that.

You mistake me. I'm *not* taking a 'we have to put in it in the OWL ontology' stance. But if we can, then I think we should. For S13 and S34 there is no choice -- there is no possible way to state the condition using RDFS/OWL.

> 
> > "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.
> >
> 
> I think the 'formal' condition addresses perfectly the problem. As for
> the 'pplain English', I don't see why "if a concept scheme S has top
> concept C, then C is a member of the scheme S."

Yes I thought of that, but then we have to explain what "member" means. And this could get confused with the property skos:member, which relates to collections. (I remember a couple of emails way back that already got skos:member confused with concept schemes.) Not necessarily a show-stopper, but would require careful wording.

> > 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...
> 
> How about these? There are not pure OWL and yet they are in the
> semantic
> conditions...
> "S13      A resource has no more than one value of skos:prefLabel per
> language."
> "S34      For any resource, every item in the list given as the value
> of
> the skos:memberList property is also a value of the skos:member
> property."

See above, for these there is no choice.

I say let's give this mystery property a name. Why not?

Cheers,

Alistair.




> 
> Cheers,
> 
> Antoine
> 
> >  (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?
> >
> > Cheers,
> >
> > Al.
> >
> > [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
> > Oxford
> > OX1 3PS
> > 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 15:32:20 UTC

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