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From: Christoffel Dhaen <christoffel@landcglobal.com>
Date: Wed, 7 Dec 2005 18:13:53 +0100
Message-ID: <28A0FFC7AEF0014AA8C2CE543AE13F5B53D2BA@x-box.quest.net>
To: "Christopher Welty" <welty@us.ibm.com>, "McBride, Brian" <brian.mcbride@hp.com>
Cc: <public-swbp-wg@w3.org>, <public-swbp-wg-request@w3.org>

Most KR systems indeed offer the option to query for both, but I must say I always assumed a SPARQL query would support transitive closure, hence would return the logical result instead of only directly asserted results. 
If both are required, the graph could solve it, but why not add the option in the query instead of having to query 2 graphs. A direct result might be requested as 
And the logical result might be requested as 

Which one should be default is debatable, but it seems to me that a lot of applications may only be interested in the logical result of the query. The option to query only direct is also very valuable to browse the graph (or parts of it), which can be used, amongst other things, in DS-systems, or search-engines (refine query).

Adding a second Closure equivalent of the property would only make querying more complicated, unless a standard to do this is defined.



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-----Original Message-----
From: public-swbp-wg-request@w3.org [mailto:public-swbp-wg-request@w3.org] On Behalf Of Christopher Welty
Sent: maandag 5 december 2005 2:20
To: McBride, Brian
Cc: public-swbp-wg@w3.org; public-swbp-wg-request@w3.org
Subject: Re: [SKOS, SPARQL, ALL] Closure and SPARQL

Yes, every KR system I've ever used provided an API for getting "asserted" 
vs. "inferred" information.  Logically they are equivalent.


Dr. Christopher A. Welty, Knowledge Structures Group
IBM Watson Research Center, 19 Skyline Dr., Hawthorne, NY  10532
Voice: +1 914.784.7055,  IBM T/L: 863.7055, Fax: +1 914.784.7455
Email: welty@watson.ibm.com
Web: http://www.research.ibm.com/people/w/welty/

"McBride, Brian" <brian.mcbride@hp.com> 
Sent by: public-swbp-wg-request@w3.org
12/03/2005 04:16 PM



I have been reviewing SPARQL last call WD on the plane as promised, and
wanted to return to an issue that David Wood had previously raised.  (No
URLs available at 30k feet - sorry)

SPARQL does not support the expression of property closures, e.g.
transitive closure.

To ground this in BP work, consider an RDF graph that includes
dc:subject properties whose values come from a SKOS taxonomy.  You
cannot express directly in SPARQL a query to find all the resources
whose dc:subject is a (possibly indirect) narrower term of some term T.

I earlier suggested that SPARQL does not have to support transitive
closure because the graph can do it.  There can be an inferencing graph
which computes the transitive closure of skos:narrower.  If you query
that graph you query the transitive closure relationship.  If you query
the ground graph you get the direct, well at least directly asserted,
relationship.  The question arises, whether there is a need to
distinguish between the direct relationship and the closure
relationship.  Are these different properties.  Should we define
skos:inNarrowerClosure (or something more appealingly named).

In terms of the plumbing, this is not necessary.  SPARQL supports
querying over multiple graphs and so can support querying the ground
graph to get at the direct relationship and an inferred graph to get at
the closed one.

However it strikes me that the direct relationship and the closure are
different relationships and it might be best practice, perhaps
generally, perhaps under certain circumstances, to define both.  I
believe the distinction to be useful.  If I am creating a graphical
representation of a SKOs taxaonomy, I want to query for the direct
relationship.  But if I'm searching for relevant resources, I probably
want the closure relationship.  If it can be useful to make this
distinction, there may be value in defining property to relate the
direct property to its closure property, e.g. ex;isTransitiveClosureOf.

I'm feeling a bit out of my depth here.  I expect this all got worked
out a while ago, but just thought I'd check.


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Received on Thursday, 8 December 2005 04:07:44 UTC

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