[DBpedia-discussion] Slow queries and inconsistent results when filtering on resource URI

[Paul Houle]

he following query runs well on the public SPARQL endpoint:
    SELECT ?type (COUNT(*) AS ?count) {
        ?station a dbo:CareerStation .
        ?who dbo:careerStation ?station .
        ?who a ?type .
    } GROUP BY ?type ORDER BY DESC(?count)

It completes in a few seconds,  the only trouble with it is that there 
are 400,000 or so YAGO types in the system,  so the query hits the 
10,000 row limit.

If I want only dbo types,  I write the following query:

    SELECT ?type (COUNT(*) AS ?count) {
        ?station a dbo:CareerStation .
        ?who dbo:careerStation ?station .
        ?who a ?type .
        FILTER(STRSTARTS(STR(?type),"http://dbpedia.org/ontology/";))
    } GROUP BY ?type ORDER BY DESC(?count)

which does not finish at all if I submit it with the rdflib sparql 
protocol client) (giving the default graph http://dbpedia.org),  failing 
with error message "Virtuoso S1T00 Error SR171: Transaction timed out"

Now that query *does* work through the web interface when it has the 
default "30000" timeout.  However,  I find then that the number of 
results depends on the timeout,  for instance with a timeout of 5000 I 
get

typecounthttp://dbpedia.org/ontology/Person
15741
http://dbpedia.org/ontology/Agent
15741
http://dbpedia.org/ontology/Athlete
12378
http://dbpedia.org/ontology/SoccerPlayer
12378
http://dbpedia.org/ontology/SoccerManager
3363
http://dbpedia.org/ontology/SportsManager
3363

and with 10000 I get

typecounthttp://dbpedia.org/ontology/Person
28962
http://dbpedia.org/ontology/Agent
28962
http://dbpedia.org/ontology/Athlete
23546
http://dbpedia.org/ontology/SoccerPlayer
23546
http://dbpedia.org/ontology/SoccerManager
5416
http://dbpedia.org/ontology/SportsManager
5416

This wasn't what I expected,  what's up?
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