Sarven Capadisli created JENA-449:
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Summary: Federated query optimization for independent queries
(with join)
Key: JENA-449
URL: https://issues.apache.org/jira/browse/JENA-449
Project: Apache Jena
Issue Type: Question
Components: ARQ, TDB
Affects Versions: TDB 0.10.1
Reporter: Sarven Capadisli
Priority: Minor
At this point I'm lead to believe that ARQ is not making an optimization before
making a federated query. Or, well, hopefully the issue has to do with my
SPARQL knowledge :)
When trying to make two federated queries (may or may not be to same endpoint),
the solution of the first graph pattern in SERVICE is projected onto the second
SERVICE. e.g.,
SELECT DISTINCT ?a ?c ?x ?y
WHERE {
{ SERVICE <http://example.org/sparql> {
?a :p ?x .
?a skos:exactMatch ?b .
} }
{ SERVICE <http://example.info/sparql> {
?c :p ?y .
?c skos:exactMatch ?d .
} }
FILTER (?b = ?c || ?d = ?a || ?a = ?c)
}
As there are no overlapping variable names in use, shouldn't each SERVICE do
its own thing independently from one another, and then the results get joined?
What I'm experiencing is that, if the first query comes back with n number of
triples, the second query is called n times. Expectation is that, each query is
called once.
See also:
http://answers.semanticweb.com/questions/22550/joining-and-filtering-federated-sparql-queries-with-a-single-request-per-service
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