Hi,
This is probably a problem with Virtuoso on the SPARQL access point
(http://dbpedia.org/sparql) but DBPedia is returning different results
depending on the values of the LIMIT clause. The LIMIT clause should
have an effect on the number of results of a query. However, I think it
should not filter out results, as it seams to happen in the following
example.
I want to retrieve the genres of all musical artists. The following query
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX dbpedia: <http://dbpedia.org/ontology/>
SELECT ?Artist ?Genre WHERE { ?Artist rdf:type
dbpedia:MusicalArtist; dbpedia:genre ?Genre . }
returns too many results hence I used OFFSET and LIMIT to split them
into manageable subsets. To have predictable sets of results I used
ORDER BY on Artist.
In the following query I was expecting to see the genres of Billie
Holiday (http://dbpedia.org/resource/Billie_Holiday) at the beginning of
the listing, but they are missing.
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX dbpedia: <http://dbpedia.org/ontology/>
SELECT ?Artist ?Genre WHERE { ?Artist rdf:type
dbpedia:MusicalArtist; dbpedia:genre ?Genre . }
ORDER BY ?Artist
OFFSET 4425
LIMIT 1000
If I increase the limit it should return more solutions per query but
overall it should return the same solutions. With a limit of 5000 the
genres of Billie Holiday show up but at a higher offset that I would expect
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX dbpedia: <http://dbpedia.org/ontology/>
SELECT ?Artist ?Genre WHERE { ?Artist rdf:type
dbpedia:MusicalArtist; dbpedia:genre ?Genre . }
ORDER BY ?Artist
OFFSET 5725
LIMIT 2000
Somehow the size of LIMIT seams to be influencing the outcome of these
queries. If it is just a problem with my SPARQL queries I would
appreciate if some could point it out to me.
Thanks in advance for you help
--
Melhores cumprimentos / Best regards
José Paulo Leal
[email protected]
http://www.dcc.fc.up.pt/~zp
+351 220 402 973
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