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Re: SKOS to RDFS/OWL ontology mapping

From: Mikael Nilsson <mini@nada.kth.se>
Date: Wed, 15 Jun 2005 13:42:05 +0200
Message-ID: <42B0140D.5060203@nada.kth.se>
To: Bernard Vatant <bernard.vatant@mondeca.com>
CC: "Miles, AJ \(Alistair\)" <A.J.Miles@rl.ac.uk>, public-esw-thes@w3.org, "Dan Brickley (E-mail)" <danbri@w3.org>
Hi!

Let me try to add some comments...

Bernard Vatant wrote:

>>>_:node1  	a:SKOS_representation		eg:People
>>>_:node1	     a:RDFS_representation		foaf:Person
>>>
>>
>>(Playing devils advocate - I'm very grateful for this discussion :) ...
>>
>>In what way are the above statements any different from e.g.
>>
>>  eg:People skos:it foaf:Person.
> 

[...]

> 
> In the blank node example, I don't express any direct relationship between the resources,
> because IMO actually there is none. They both are representaions of some "ineffable
> subject" which might live beyond/before any representation, but on which existence we
> should keep agnostic they are both "fingers pointing at the moon", but somehow indicating
> it. As I posted an hour ago on my blog, I came this morning to this surprising conclusion
> : "subjects have no identity, only representations have one". Note that I say subject here
> to refer to what TM folks used to call "non-addressable subject". So 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".

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

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

You must look closer at the definition of "having identity". I believe 
one good definition is "being separable from other things". 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...

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!).

> 
> 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.

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.

And I am still not entirely convinced that foaf:Person and ex:People are 
not identical (sameResource). What are the arguments that they are 
different?

/Mikael



-- 
Plus ça change, plus c'est la même chose

Received on Wednesday, 15 June 2005 11:42:29 UTC

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