Vocab AND Ontology?

[Tony Linde]

Hi Bernard,

Thanks for that.

> I tried to make before

I did remember that which was why I wanted 'to hear from the
vocabulary/ontology experts'.

> documents/data about "White Dwarf Stars", a SKOS concept "White Dwarf
> Stars" is what you need, and the position of this concept in a Concept
> Scheme hierarchy, and its association with other concepts such as
> "Chandrasekhar Limit".

I don't recall any concept linking proposed for vocabs apart from the
narrower/broader relationships. What would you term this relationship and
how would it be recorded in SKOS? I assumed this sort of relationship was
better modelled in an ontology.

> - If you want to classify objects, find them using logical inference,

I'm not sure we do want to classify individual objects so much as classify
datasets, queries, papers, people even? But maybe that is what you meant.

> topic. But you don't find "Chandrasekhar Limit" at all in the star
> ontology, although it's a very pertinent concept in stellar

I know I'm exposing my lack of knowledge about ontologies, but that's what
these lists are for - to learn something new from others. Why can we not add
"Chandrasekhar Limit" as a concept in an ontology? Does every concept have
to be a class of physical things? Can things not have a relationship with
this concept of either 'beyond' or 'within'?

BTW - some of the things I've read before:
  'A formal ontology is a controlled vocabulary expressed in an ontology
representation language.' 
(http://www.metamodel.com/article.php?story=20030115211223271)

  'ontologies are specified in the form of definitions of representational
vocabulary'
(http://informationr.net/ir/6-2/paper94.html)

'map the relations between differing vocabularies, and pinpoint the location
of properties within a larger ontological framework of interconnected
knowledge, interconnected via the relationships established within an
ontology'
(http://xml.coverpages.org/ni2001-02-28-d.html)

I'd be interested in your take on these documents (and many others beside)
and why you think, either they've got it wrong or they're talking about
something different than we are in this thread. I'm not trying to dispute
your expert opinion but showing how I came to the conclusion that a
vocabulary might be contained within an ontology.

Cheers,
Tony. 

> -----Original Message-----
> From: Bernard Vatant [mailto:bernard.vatant at mondeca.com]
> Sent: 24 September 2007 15:16
> To: Tony Linde
> Cc: semantics at ivoa.net
> Subject: Re: Vocab AND Ontology?
> 
> Tony, and all
> 
> On the OWL vs SKOS debate, I would like to quickly stress again a point
> I tried to make before
> http://www.ivoa.net/forum/semantics/0709/0362.htm
> ... but which was maybe blurred by other points in this verbose message
> ;-) .
> 
> SKOS is not a "low-level-semantics" OWL, because SKOS and OWL have not
> the same functional aims. Again, re-read above message for more
> details.
> Choosing either one of those representations, or both, should not be
> based on feasibility/complexity of representation, but on functional
> objectives. Let me take an example illustrated in both Ed's Star
> ontology and IAU Thesaurus, the "White Dwarf Star" concept
> - If you are a documentalist want to index/search/retrieve
> documents/data about "White Dwarf Stars", a SKOS concept "White Dwarf
> Stars" is what you need, and the position of this concept in a Concept
> Scheme hierarchy, and its association with other concepts such as
> "Chandrasekhar Limit".
> - If you want to classify objects, find them using logical inference,
> an
> OWL class "White Dwarf Star" is what you need, with its necessary
> conditions, attached properties, position in a subsumption tree etc.
> 
> If you want both uses, you need both representations, BUT : *you can't
> expect to automatically and safely transform one representation into
> the
> other automatically*.
> - From SKOS to OWL : not every concept defined in a SKOS concept
> scheme,
> and used for indexing/search/retrieval makes sense as a class in a OWL
> ontology. See the "cosmology example" in my previous message.
> - From OWL to SKOS : only concepts represented as classes would be
> available for indexing, so you would have to add indexing concepts
> which
> were not present as OW classes.
> 
> Look at White Dwarf in IAU Thesaurus and in star ontology. In the
> former
> you find the related concept "Chandrasekhar Limit", which makes perfect
> sense for indexing, because there is a lot of litterature for which
> Chandrasekar limit is a relevant indexing concept, and even the primary
> topic. But you don't find "Chandrasekhar Limit" at all in the star
> ontology, although it's a very pertinent concept in stellar
> astrophysics, but there again it's perfectly normal because this
> concept
> does not fit in as a class, nor even as an individual or property
> value.
> One can imagine a formal definition of the white darf class including
> indirectly this concept by putting a constraint on the mass (although
> this is tricky in OWL), but you get the picture.
> 
> This example again to illustrate why I'm concerned about any
> methodology
> based on : let's do SKOS first, and then we will transform into OWL, or
> the other way round.
> 
> Bernard
> 
> Tony Linde a écrit :
> >> Correspondingly, the OWL is
> >> trivially produced from either format if you're interested (some of
> >> us are definitely NOT).
> >>
> >
> > This seems the core question, Rick (whatever the starting point and I
> agree
> > that the IAU Thesaurus seems a good one from my naive pov): do we
> produce
> > the SV in OWL and derive the SKOS or produce it in SKOS and derive
> the OWL?
> >
> > I'd still plump for the former for the following reasons:
> >
> > a. either approach seems, at the outset, to involve little cost
> (though I'd
> > still assert that the availability of Protege and other ontology
> tools make
> > this a cheaper route);
> >
> > b. any extensions to the ontology will break the link between
> vocabulary and
> > ontology since the extensions could not be derived from the vocab so
> we
> > could well end up with divergent terms meaning the same thing;
> >
> > c. it seems that no matter how the ontology (with vocab included) is
> > extended, we can still derive the vocabulary providing we mandate
> that vocab
> > terms use the classes and relationships specified.
> >
> > This is a fairly simplistic view, I know. Can anyone show any
> methodological
> > or technical problem with this approach (I don't think Rick pointed
> out any
> > real problems with the OWL-based approach: what ontological baggage
> might
> > cause problems)?
> >
> > And this is still only my view - others will have their own position
> on the
> > question above.
> >
> > T.
> >
> >
> >> -----Original Message-----
> >> From: owner-semantics at eso.org [mailto:owner-semantics at eso.org] On
> >> Behalf Of Frederic V. Hessman
> >> Sent: 24 September 2007 10:14
> >> To: semantics at ivoa.net
> >> Subject: Re: Vocab AND Ontology?
> >> ...
> >>
> >
> >
> >
> >
> 
> --
> 
> *Bernard Vatant
> *Knowledge Engineering
> ----------------------------------------------------
> *Mondeca**
> *3, cité Nollez 75018 Paris France
> Web:    www.mondeca.com <http://www.mondeca.com>
> ----------------------------------------------------
> Tel:       +33 (0) 871 488 459
> Mail:     bernard.vatant at mondeca.com
> <mailto:bernard.vatant at mondeca.com>
> Blog:    Leçons de Choses <http://mondeca.wordpress.com/>
>