Hi,
I noticed the following issue on the DBpedia endpoint and the LOD cache
(http://dbpedia.org/sparql, http://lod.openlinksw.com/sparql):
I did not have time to try it against a develop7 git branch.
The following query works as expected and returns fast: It apparently scans the
approx. 600 classes and filters them by their label matching the regex:
Select ?x {
?x <http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<http://www.w3.org/2002/07/owl#Class> .
?x <http://www.w3.org/2000/01/rdf-schema#label> ?v_3 .
Filter(regex(?v_3, "airport", "i")) .
Filter(langMatches(lang(?v_3), "en")) .
} Limit 10
The following query takes very long to complete. Apparently the query planner
decides to start with bif:contains, thereby scanning all instances that have
'airport' in their name - which is a much larger set than filtering just by the
classes first:
Select ?x {
?x <http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<http://www.w3.org/2002/07/owl#Class> .
?x <http://www.w3.org/2000/01/rdf-schema#label> ?v_3 .
Filter(<bif:contains>(?v_3, "airport")) .
Filter(langMatches(lang(?v_3), "en")) .
} Limit 10
I am wordering if there are already planned enhancements for this issue.
Cheers,
Claus
--
Dipl. Inf. Claus Stadler
Department of Computer Science, University of Leipzig
Research Group: http://aksw.org/
Workpage & WebID: http://aksw.org/ClausStadler
Phone: +49 341 97-32260
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