[jira] [Created] (JENA-449) Federated query optimization for independent queries (with join)

["Sarven Capadisli (JIRA)" <ji...@apache.org>]

Sarven Capadisli created JENA-449:
-------------------------------------

             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

--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira