[Building Sakai] SPARQL structure/time issue

[Cliff, David Graeme]

Never mind, I've managed to get decent return times by breaking up my queries. The below CONSTRUCT actually works quite well, it was my combined PI, CO-PI CONSTRUCT statement that made the server stumble around.

Cheers,
David

From: Cliff, David Graeme
Sent: Thursday, April 26, 2012 9:45 AM
To: 'sakai-dev at collab.sakaiproject.org'
Subject: SPARQL structure/time issue

Hi all,

I get the sneaking suspicion that the SPARQL I'm running could be better structured, as it takes a long time to return, and was wondering if anyone had any ideas how I might reorganize it.

SELECT  (COUNT(DISTINCT ?pirole) AS ?count)
WHERE
{
                ?pirole a <http://vivoweb.org/ontology/core#PrincipalInvestigatorRole> ;
                                ?a ?b .
                NOT EXISTS {?pirole <http://vivoweb.org/ontology/core#principalInvestigatorRoleOf> ?x}
}

That query takes almost 10 minutes to return, and the result is 22529. If I drop the ?a ?b (obviously not needed for a count) it comes back in reasonable time. However that's not really an option for the CONSTRUCT query I run, and its this that the server has a very hard time dealing with.

CONSTRUCT
{
                ?pirole ?a ?b .
}
WHERE
{
                ?pirole a <http://vivoweb.org/ontology/core#PrincipalInvestigatorRole> ;
                                ?a ?b .
                NOT EXISTS {?pirole <http://vivoweb.org/ontology/core#principalInvestigatorRoleOf> ?x}
}

Any ideas?

- David
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