Module org.apache.jena.arq

Package org.apache.jena.sparql.algebra.optimize

Class TransformFilterImplicitJoin

java.lang.Object

org.apache.jena.sparql.algebra.TransformCopy

org.apache.jena.sparql.algebra.optimize.TransformFilterImplicitJoin

All Implemented Interfaces:

Transform

public class TransformFilterImplicitJoin
extends TransformCopy

Optimizer for transforming implicit joins. These covers queries like the following:

 SELECT *
 WHERE
 {
   ?s a ?type1 .
   ?t a ?type2 .
   FILTER(?s = ?t)
 }
 

Clearly this is a trivial example but doing this optimization can have big performance gains since it can completely eliminate cross products that we would otherwise be required to evaluate. The optimization where applicable results in a query of the following form:

 SELECT *
 WHERE
 {
   ?s a ?type1 .
   ?s a ?type1 .
   BIND(?s AS ?t)
 }
 

The optimizer does not cover the implicit left join case, for that see TransformImplicitLeftJoin

Applicability

This optimization aims to eliminate implicit joins of the form ?x = ?y or SAMETERM(?x, ?y), the latter can almost always be safely eliminated while the former may only be eliminated in the case where we can guarantee that at least one of the variables is a non-literal e.g. it occurs in the subject/predicate position. In the case where this is not true the optimization may not be made since we cannot assume that we can map value equality to term equality by making the optimization.

Known Limitations/To Do

• Application to implicit joins may block the sequence transform which means the potential benefits of the optimization are negated

Field Summary

Fields inherited from class org.apache.jena.sparql.algebra.TransformCopy

COPY_ALWAYS, COPY_ONLY_ON_CHANGE

Constructor Summary

Constructors

Constructor	Description
TransformFilterImplicitJoin()

Method Summary

Modifier and Type	Method	Description
Op	transform(OpFilter opFilter, Op subOp)

Methods inherited from class org.apache.jena.sparql.algebra.TransformCopy

transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform, transform

Methods inherited from class java.lang.Object

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

Constructor Details

TransformFilterImplicitJoin

public TransformFilterImplicitJoin()

Method Details

transform

public Op transform(OpFilter opFilter,
 Op subOp)

Specified by:

transform in interface Transform

Overrides:

transform in class TransformCopy