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Re: [SKOS] The return of ISSUE-44 (was Re: TR : SKOS Reference Editor's Draft 23 December 2007)

From: Bernard Vatant <bernard.vatant@mondeca.com>
Date: Thu, 10 Jan 2008 18:48:56 +0100
Message-ID: <47865A88.4050108@mondeca.com>
To: Daniel Rubin <rubin@med.stanford.edu>
Cc: Antoine Isaac <aisaac@few.vu.nl>, SKOS <public-esw-thes@w3.org>, SWD WG <public-swd-wg@w3.org>

Hi Daniel
>>
>> As is well stated in the introduction of the editor's draft, the 
>> intended use of SKOS, not to support inference, but to support 
>> indexing/classification, search and retrieval of resources.
>
> Classification is a type of inference, and indexing/retrieval will 
> require inference at least along hierarchical relations for query 
> expansion, so I don't see that we can easily keeps separate from the 
> need to support inference (albeit simple inference)...
Well, let me clarify. The kind of inference you mention can be performed 
by different tools in various functional implementations based on 
various interpretations of relations (hierarchical or not). For example, 
for whatever reason, the query expansion might want to follow the 
hierarchy upwards and/or downwards for a specific number of steps (1, 2, 
n), or until it finds a reasonable number of answers, or follow also the 
"related" links one step across, whatever. IOW, different 
implementations will retrieve different sets of answers for the same query.
What I meant by inference is inference based on the formal semantics, 
for which any tool implementing correctly the semantics has to get the 
same results, e.g. a SPARQL request on a given RDF graph.

Let me take an example. Suppose we have.

a:X     skos:narrower   a:Z1
a:Z1     skos:narrower   a:Z2
a:Z1    skos:related   a:Z4
a:Z2     skos:narrower   a:Z3

:R1     skos:subject      a:Z1
:R2     skos:subject      a:Z2
:R3     skos:subject      a:Z3
:R4     skos:subject      a:Z4

And a query expansion downwards from a:X

SELECT    ?r
WHERE    {?r  skos:subject  ?c.
                   a:X  skos:narrower  ?c.}

Following SKOS semantics this will retrieve { :R1 } since skos:narrower 
is not transitive. And it's OK.

But nothing prevents an application to expand the query by whatever 
specific mean it sees fit in the context
- Expand recursively along skos:narrower,  retrieves {:R1, :R2, :R3}
- Expand 2 steps along skos:narrower, retrieves {:R1, :R2}
- Expand 2 steps along either skos:narrower or skos:related, retrieves 
{:R1, :R2, :R4}

etc ...

In a nutshell, SKOS relations will support functional semantics of the 
search engine, but does not enforce any specific semantics. And I think 
it's OK.

Bernard






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Received on Thursday, 10 January 2008 17:49:16 GMT

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