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Graph to retrieve DESCRIBE result from

From: Kjetil Kjernsmo <Kjetil.Kjernsmo@computas.com>
Date: Thu, 19 Mar 2009 15:55:24 +0100
To: 'RDF Data Access Working Group' <public-rdf-dawg@w3.org>
Message-Id: <200903191555.24240.Kjetil.Kjernsmo@computas.com>
All,

Our latest application makes extensive use of named graphs, but it has 
also been the source of much confusion. 

We haven't documented most of this confusion very well, since we are 
focused on pragmatic solutions to problems. I hope to document and 
share more of these problems, as I believe it can be quite nice to have 
to clarify the spec. I just want to make sure that we're not just being 
silly before sharing it. :-) 

There is however, one case that I brought up on the Virtuoso list last 
year that I feel would be interesting to discuss. The discussion begins 
with this message (which is part of a longer thread), and the responses 
to it:

http://sourceforge.net/mailarchive/message.php?msg_name=200901051326.51443.Kjetil.Kjernsmo%40computas.com

The essence is that we have a default graph which has only triples that 
state the types of the graphs we have. Then, without knowing the exact 
graph names (which may be added after the queries are coded into the 
application), we should be able identify the needed graphs, and then identify 
the URIs by using
 
?g a <http://msone.computas.no/graphs/vocab/mediasone#InstanceGraph> .
GRAPH ?g 
{
?uri ms:coverArt <http://ruby3.computas.no/covers/nfi/48739.jpg> .
}

If I DESCRIBE ?uri, this should give me the triples from the 
<#InstanceGraph> with ?uri as subject, and they do in this case exist 
(otherwise the example would be moot).

What the linked email shows is that this strategy doesn't work in 
Virtuoso with DESCRIBE, but it sort of works with CONSTRUCTs (but can't 
be used in our app since we do not have Feature:LimitByResource). 

Indeed, I find nothing in the SPARQL 1 spec that would say it should 
work, but I think it should. :-) 

I have not identified the concrete problems that would have to be solved 
for this to work, so I'm just throwing the ball in the hope that 
someone with a deeper understanding than me will identify those 
problems.

Kind regards 

Kjetil Kjernsmo
-- 
Senior Knowledge Engineer
Mobile: +47 986 48 234
Email: kjetil.kjernsmo@computas.com   
Web: http://www.computas.com/

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Received on Thursday, 19 March 2009 15:00:10 GMT

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