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Re: SKOS, owl:sameAs and DBpedia

From: Yves Raimond <yves.raimond@gmail.com>
Date: Wed, 24 Mar 2010 16:19:28 +0000
Message-ID: <82593ac01003240919ma59a84aiac4ab7177ccb82f3@mail.gmail.com>
To: Dan Brickley <danbri@danbri.org>
Cc: Linking Open Data <public-lod@w3.org>
>>>> Is that an issue? Should we drop SKOS altogether if we go on with
>>>> that, or should we use skos:exactMatch instead of owl:sameAs?
>>>
>>> see also http://wiki.foaf-project.org/w/term_focus
>>>
>>> I'm running out of excuses for not having added this already...
>>
>> Great, thanks for the link!
>>
>> However, I'd like to understand why a sameAs would be bad here, I have
>> the intuition it might be, but am really not sure. It looks to me like
>> there's no resource out there that couldn't be a SKOS concept as well
>> (you may want to use anything for categorisation purpose --- the loose
>> "categorisation" relationship being encoded in the predicate, not the
>> type). If it can't be, then I am beginning to feel slightly
>> uncomfortable about SKOS :-)
>
> Because conceptualisations of things as SKOS concept are distinct from
> the things themselves. If this weren't the case, we couldn't have
> diverse treatment of common people/places/artifacts in multiple SKOS
> thesauri, since sameAs merging would mangle the data. SKOS has lots of
> local administrative info attached to each concept which doesn't make
> sense when considered to be properties of the thing the concept is a
> conceptualization of.
>
>> I am sure this problem must have been looked at before, e.g. within LCSH?
>
> Yes, this has been discussed since we brought SKOS into W3C from the
> SWAD-Europe project ~2004. There is some discussion in this old guide
> -
>
> http://www.w3.org/TR/2005/WD-swbp-skos-core-guide-20051102/#secmodellingrdf
>
> 'There is a subtle difference between SKOS Core and other RDF
> applications like FOAF [FOAF], in terms of what they allow you to
> model. SKOS Core allows you to model a set of concepts (essentially a
> set of meanings) as an RDF graph. Other RDF applications, such as
> FOAF, allow you to model things like people, organisations, places
> etc. as an RDF graph. Technically, SKOS Core introduces a layer of
> indirection into the modelling.'
>
> 'The above graph describes a relationship between a concept, and the
> person who is the creator of that concept. This graph should be
> interpreted as saying,
> "the person named 'Alistair Miles' is the creator of the concept
> denoted by the URI http://www.example.com/concepts#henry8. This
> concept was modified on 2005-02-06."
> This graph should probably not be interpreted as saying, "the person
> named 'Alistair Miles' is the creator of King Henry VIII," or that,
> "King Henry VIII was modified on 2005-02-06".
>
> 'This second graph should probably be interpreted as saying,
> "the persons named 'King Henry VII' and 'Elizabeth of York' are the
> creators of the person named 'King Henry VIII'."
>
> So, for a resource of type skos:Concept, any properties of that
> resource (such as creator, date of modification, source etc.) should
> be interpreted as properties of a concept, and not as properties of
> some 'real world thing' that that resource may be a conceptualisation
> of.
>
> This layer of indirection allows thesaurus-like data to be expressed
> as an RDF graph. The conceptual content of any thesaurus can of course
> be remodelled as an RDFS/OWL ontology. However, this remodelling work
> can be a major undertaking, particularly for large and/or informal
> thesauri. A SKOS Core representation of a thesaurus maps fairly
> directly onto the original data structures, and can therefore be
> created without expensive remodelling and analysis.
>
> SKOS Core is intended to provide both a stable encoding of
> thesaurus-like data within the RDF graph formalism, as well as a
> migration path for exploring the costs and benefits of moving from
> thesaurus-like to RDFS/OWL-like modelling formalisms.'
>
> http://www.w3.org/TR/2005/WD-swbp-skos-core-guide-20051102/#secidentity
>
> 'Concept Identity and Mapping
>
> The property owl:sameAs should not be used to express the fact that
> two conceptual resources (i.e. resources of type skos:Concept) share
> the same meaning. The property owl:sameAs implies that two resources
> are identical in every way (they are in fact the same resource).
> Although two conceptual resources may have the same meaning, they may
> have different owners, different labels, different documentation,
> different history, and of course a different future.'
>
> Hope this helps,

It definitely does! Thanks for all that!

Now, I guess we need to sort out whether we really need this level of
indirection (the data specific to our categorisation scheme is very
bare-bone, and only useful in some very specific cases).

Many thanks,
y


>
> Dan
>
Received on Wednesday, 24 March 2010 16:20:01 UTC

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