same and synonym Re: IAU thesaurus in RDF (an update)

Ed
> Is infrared_radiation synonymous with infrared_emission? I don't see
> a way for SKOS to say SameAs. How does one say iau:stars sameas
> cds:stars?

This is a complex issue - and to say the truth my favourite one - with different aspects. So I have to bite here :-)

1. Synonymy is dealt with in SKOS as in standard thesaurus practice. Defining a controlled vocabulary is all about defining a sort of closed linguistic world where the "unique name assumption" holds, which means distinct concepts bear distinct labels, and every concept has a single (preferred) label (in a given language). So if you have synonymous like "infrared emission" and "infrared radiation" (supposing they are actually synonymous, which IMHO seems questionable, but this is not the point), the controlled vocabulary authority, based on what is considered as the best naming practice. Suppose you recommend "infrared radiation" over "infrared emission", you will have in classical thesaurus :

/Infrared Emission

    /USE Infrared Radiation/
/
Infrared Radiation

    UF /Infrared Emission
/
In SKOS, the same semantics is achieved using skos:prefLabel and skos:altLabel.

iau:_123456  skos:prefLabel   'infrared radiation' @en
iau:_123456  skos:altLabel   'infrared emission' @en
iau:_123456  skos:prefLabel   'rayonnement infrarouge' @fr
iau:_123456  skos:altLabel   'émission infrarouge' @fr

Note that I deliberately used some opaque string for the concept URI, to make clear that this is a question concerning labels and not concepts themselves. There is only one concept here, with four labels.

2. A different issue arises when two different authorities have issued vocabularies and you want to declare a posteriori equivalence of such concepts. SKOS does not prevent you to use owl:sameAs to express such an equivalence, since skos:Concepts are individuals. If you look e.g. at http://www.geonames.org/ontology/ontology_v2.0_Lite.rdf, you will see that I have defined here a few owl:sameAs equivalences between geographical feature codes (a subclass of skos:Concept) and concepts defined by the environmental GEMET thesaurus (also in SKOS).

So something like the following would be perfectly consistent with both OWL and SKOS semantics

iau:stars   rdf:type   skos:Concept
cds:stars   rdf:type   skos:Concept
iau:stars   owl:sameAs   cds:stars

Of course, you might want things more subtle than that, because for some reason you want to declare a mapping without merging the two concepts. In that case you can use SKOS mapping properties, but note that this draft has no formal status whatsoever so far on W3C track. See http://www.w3.org/2004/02/skos/mapping/spec/

Hopes that helps

Bernard
/
/

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*Bernard Vatant
*Knowledge Engineering
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