org.openrdf.query.algebra.evaluation.impl
Class QueryJoinOptimizer.JoinVisitor

java.lang.Object
  org.openrdf.query.algebra.helpers.QueryModelVisitorBase<RuntimeException>
      org.openrdf.query.algebra.evaluation.impl.QueryJoinOptimizer.JoinVisitor

All Implemented Interfaces:

QueryModelVisitor<RuntimeException>

Enclosing class:

QueryJoinOptimizer

protected class QueryJoinOptimizer.JoinVisitor
extends QueryModelVisitorBase<RuntimeException>

Constructor Summary

protected

QueryJoinOptimizer.JoinVisitor()

Method Summary

protected void	getJoinArgs(TupleExpr tupleExpr, List<TupleExpr> joinArgs)
void	meet(Join node)
protected TupleExpr	selectNextTupleExpr(List<TupleExpr> expressions, Set<String> boundVars) Selects from a list of tuple expressions the next tuple expression that should be evaluated.
protected List<TupleExpr>	sortExpressions(List<TupleExpr> expressions, Set<String> boundVars) Merges the boolean constraints and the path expressions in one single list.

Methods inherited from class org.openrdf.query.algebra.helpers.QueryModelVisitorBase

meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meet, meetBinaryTupleOperator, meetBinaryValueOperator, meetCompareSubQueryValueOperator, meetNode, meetOther, meetSubQueryValueOperator, meetUnaryTupleOperator, meetUnaryValueOperator

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

QueryJoinOptimizer.JoinVisitor

protected QueryJoinOptimizer.JoinVisitor()

Method Detail

meet

public void meet(Join node)

Specified by:

meet in interface QueryModelVisitor<RuntimeException>

Overrides:

meet in class QueryModelVisitorBase<RuntimeException>

getJoinArgs

protected void getJoinArgs(TupleExpr tupleExpr,
                           List<TupleExpr> joinArgs)

sortExpressions

protected List<TupleExpr> sortExpressions(List<TupleExpr> expressions,
                                          Set<String> boundVars)

Merges the boolean constraints and the path expressions in one single list. Path expressions are heuristically reordered to minimize query evaluation time and boolean constraints are inserted between them. The separate boolean constraints are moved to the start of the list as much as possible, under the condition that all variables that are used in the constraint are instantiated by the path expressions that are earlier in the list. An example combined list might be: [(A,B,C), A != foo:bar, (B,E,F), C != F, (F,G,H)].

selectNextTupleExpr

protected TupleExpr selectNextTupleExpr(List<TupleExpr> expressions,
                                        Set<String> boundVars)

Selects from a list of tuple expressions the next tuple expression that should be evaluated. This method selects the tuple expression with highest number of bound variables, preferring variables that have been bound in other tuple expressions over variables with a fixed value.