Il 11/2/2011 1:43 PM, Patrick van Kleef ha scritto:
> Hi Roberto,
>
>> try several times this simple query on http://lod.openlinksw.com/sparql
>> (default dataset name: http://dbpedia.org):
>> #############
>> SELECT COUNT(DISTINCT ?movie) WHERE {
>> ?movie a dbpedia-owl:Film.
>> ?movie rdfs:label ?label.
>> FILTER ( lang(?label) = "en" )
>> }
>> #############
>> You will get each time a different number. :-)
>> Now, if you try the same query on http://dbpedia.org/sparql, you wil get
>> the "correct" number (at least it does not change!): 60222
>>
>> If you remove the filter condition, you will get the same result.
>
> Did you notice that on http://lod.openlinksw.com/sparql page, the
> field Execution Timeout is set to 15000 ?
>
Great! Thank you very much Patrick! I was sure that someone from
OpenLink Software would have answered to me. :-)
Just to take advantage of you, is there a way to setting this parameter
for similar queries programmatically, e.g., via Java code? At the moment
with Java I use Jena and the sparqlService:
#######################
Query query = QueryFactory.create("SELECT ...");
QueryExecution qexec =
QueryExecutionFactory.sparqlService("http://lod.openlinksw.com/sparql";,
query, "http://dbpedia.org";);
try {
ResultSet results = qexec.execSelect();
while (results.hasNext()) {
...
}
} finally {
qexec.close();
}
#######################
> This enables the ANYTIME[1] query option in Virtuoso, which ensures
> that Virtuoso will return with whatever records it has found in 15000
> msec, or about 15 seconds of processing time. Depending on other
> queries running, this amount will be different between successive runs
> explaining the difference you are seeing.
>
> If you retry your query, but set the field to 0 or empty, then you get
> similar behaviour to http://dbpedia.org/sparql and will return 60022.
>
> Note that on both machines there are (different) maximum timeouts set,
> to make sure everyone gets an even share of the resources available on
> these services.
>
> See also:
> [1] http://docs.openlinksw.com/virtuoso/anytimequeries.html
>
> Patrick
> ---
> OpenLink Software
--
roberto mirizzi
http://sisinflab.poliba.it/mirizzi
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