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RE: SKOS to RDFS/OWL ontology mapping

From: Bernard Vatant <bernard.vatant@mondeca.com>
Date: Wed, 15 Jun 2005 16:01:36 +0200
To: "Mikael Nilsson" <mini@nada.kth.se>
Cc: <public-esw-thes@w3.org>
Message-ID: <GOEIKOOAMJONEFCANOKCMEPFGCAA.bernard.vatant@mondeca.com>


Hi Michael

> Let me try to add some comments...

You're welcome :))

> Bernard Vatant wrote:

> > ... blank nodes are the best way to "capture" implicitly
> > this subject without identifying it to a resource, which,
> > I agree with what you wrote a few posts ago, would lead us to recursive definitions.

> Well, I think there are several issues with this argument.
>
> First, Alistair might define A skos:it B to mean:
>    "B is the RDFS representation of the 'subject' that has A as SKOS
>     representation".

Sure it might. And keep agnostic about what this subject is. Although this declaration is
not symetric.
Is it made from eg: or foaf: namespaces' publishers viewpoint?

> This shows that even though you might not perceive a direct relationship
> between the two, I can come up with a perfectly valid property to
> "shortcut" any indirect relation.

Agreed

> Put another way, the existence of an
> intermediate node does not preclude the use a direct property to
> describe this relationship. Such a relationship can even be expressed in
> OWL and so inferred automatically...

Well, that sets another issue: What do we want this kind of assertion for? To make some
kind of inference, and if so, which kind? My view was that what we want to capture here is
at a level on which any inference would be risky.

> See below, however, for reasons for
> not wanting to do it using direct properties anyway.

We'll see :))

> Second, you say "subjects have no identity". Unfortunately you
> contradict this by giving the (admittedly blank) subject node the
> (locally valid) identifier _:node1.

I don't see any contradiction. The subject is not the node. The node is identified OK,
although only locally, but not the subject itself which is only implicitely defined.
Otherwise I won't use a blank node, I would define a resource, and assign an URI, and go a
stage further in recursivity trap : what is the type of this resource, what are its
properties etc. All the point is indeed to have the subject not identified to/by any
resource, or any identifier of this resource. The node *is* not the subject.

> You must look closer at the definition of "having identity".

Hmm. Let's say I can claim this is something I have looked at quite closely for a certain
number of years now - maybe to the point of blindness, though :)) See
http://universimmedia.blogspot.com/

> I believe one good definition is "being separable from other things".

I buy it. But separation in things is only possible in representations, because things
exist only in representations. What I claim is that our "subject of conversation" is never
identified as such, its'not an owl:Thing. We identify representations, and at some point
we want to link two representations. Note that each representation taken standalone is
built on specific logic rules. So logical integration of two different representation
spaces is most of the time impossible if they are built on different logical frameworks.

> So if you are giving your subject a blank node, it is very much separable from
> other things. Indeed that is the very reason you create this blank node
> - to be able to *identify* the subject of your properties...

"The node is separable from other nodes" does not mean "the subject is separable from
other subjects". In Quantum Mechanics, there are a lot of situations of that kind ... I
can define another node including e.g.  b:Human and  eg:People. As a node, it will be
distinct from the previous one, but the fact that they are about the same or different
subject is undecidable, basically.

Look at Google News, and tell me what is a News subject, and how it's identified ...

> If something does not have an identity, you cannot even use a blank node
> to refer to it (because that shows it has an identity!).

Nope. I have a Welfare number, an E-mail, a few Web Pages ... all of those identify some
representation of me in a certain context. Every context has its own logic. You can grab
an arbitrary number of those resources together in a node, that does not mean you captued
my identity.

> > Moreover, the blank node option allows you to gather as many resources as you want, be
> > they in a formal scheme or not.
> >
> > _:node1  	a:SKOS_representation		eg:People
> > _:node1	     a:RDFS_representation		foaf:Person
> > _:node1	     a:Wikipedia_definition	http://en.wikipedia.org/wiki/Person

> Now, this is an argument for using a separate node (blank or not). This
> is of course not doable using skos:it.

This actually is very Topic Map-ish. Looks like a TM N-ary association, basically.

> However, is this needed? are there really N different paradigms?
> Is not the Wiki node compatible with SKOS concepts?
> So we would have only two domains.

Yes, I think a SKOS ConceptScheme, a RDFS or OWL ontology, and Wikipedia are really
different representation spaces, or paradigms if you like. You can't merge them.

> And I am still not entirely convinced that foaf:Person and ex:People are
> not identical (sameResource).

You mean really ...

eg:People 	owl:sameAs	foaf:Person

... in that case take your responsibility for all resulting semantic damage. I won't sort
out the mess :)

> What are the arguments that they are different?

Show me a valid argument that they could be the same. For one they have not the same type.
And certainly you can infer properties of the first that will seem very weird when applied
to the other.

Cheers

Bernard

**********************************************************************************

Bernard Vatant
Senior Consultant
Knowledge Engineering
bernard.vatant@mondeca.com

"Making Sense of Content" :  http://www.mondeca.com
"Everything is a Subject" :  http://universimmedia.blogspot.com

**********************************************************************************
Received on Wednesday, 15 June 2005 14:01:56 UTC

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