Examples of de.fuberlin.wiwiss.d2rq.algebra.JoinOptimizer

de.fuberlin.wiwiss.d2rq.algebra.JoinOptimizer

Removes unnecessary joins from a {@link TripleRelation} in caseswhere this is possible without affecting the result. This is an optimization.

A join J from table T1 to table T2 with join condition T1.c_1 = T2.c_1 && T1.c_2 = T2.c_2 && ... can be removed if these conditions hold:

The only join mentioning T2 is J.
All columns of T2 that are selected or constrained or used in an expression occur in J's join condition.
All values of T1.c_n are guaranteed to occur in T2.c_n, that is, there is a foreign key constraint on T1.c_n.

In this case, J can be dropped, and all mentions of T2.c_n can be replaced with T1.c_n.

TODO: Currently this only is used for TripleRelations in FindQuery but it could be used for NodeRelations in SPARQL queries too TODO: Prune unnecessary aliases after removing joins @author Richard Cyganiak (richard@cyganiak.de)

          && predicateChecker.canMatch(tripleRelation.nodeMaker(TripleRelation.PREDICATE))
          && objectChecker.canMatch(tripleRelation.nodeMaker(TripleRelation.OBJECT))) {
        subjectChecker.addPotentialMatch(tripleRelation.nodeMaker(TripleRelation.SUBJECT));
        predicateChecker.addPotentialMatch(tripleRelation.nodeMaker(TripleRelation.PREDICATE));
        objectChecker.addPotentialMatch(tripleRelation.nodeMaker(TripleRelation.OBJECT));
        TripleRelation r = new JoinOptimizer(selectedTripleRelation).optimize();
        if (limitPerRelation != Relation.NO_LIMIT) {
          r = r.limit(limitPerRelation);
        }
        result.add(r);
      }

Examples of de.fuberlin.wiwiss.d2rq.algebra.JoinOptimizer

Related Classes of de.fuberlin.wiwiss.d2rq.algebra.JoinOptimizer