com.hp.hpl.jena.sparql.algebra.optimize
Class TransformFilterInequality

java.lang.Object
  com.hp.hpl.jena.sparql.algebra.TransformCopy
      com.hp.hpl.jena.sparql.algebra.optimize.TransformFilterInequality

All Implemented Interfaces:

Transform

public class TransformFilterInequality
extends TransformCopy

A transform that aims to optimize queries where there is an inequality constraint on a variable in an attempt to speed up evaluation e.g

 PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
 SELECT *
 WHERE
 {
   ?s rdf:type <http://type> ;
      ?p ?o .
   FILTER(?p != rdf:type)
 }
 

Would transform to the following:

 PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
 SELECT *
 WHERE
 {
   ?s rdf:type <http://type> ;
      ?p ?o .
   MINUS { VALUES ?p { rdf:type } }
 }
 

Status

Performance testing has shown that often this gives minimal performance benefit so this optimization is not enabled by default. It may be explicitly enabled by setting the ARQ.optFilterInequality symbol in your Context or the ARQ global context (ARQ.getContext() to true

Applicability

This optimizer is conservative in that it only makes the optimization where the inequality constraint is against a non-literal as otherwise substituting the value changes the query semantics because it switches from value equality to the more restrictive term equality. The optimization is safe for non-literals because for those value and term equality are equivalent (in fact value equality is defined to be term equality).

There are also various nested algebra structures that can make the optimization unsafe and so it does not take place if any of those situations is detected.

Field Summary

Fields inherited from class com.hp.hpl.jena.sparql.algebra.TransformCopy

COPY_ALWAYS, COPY_ONLY_ON_CHANGE

Constructor Summary

TransformFilterInequality()
Creates a new transform

Method Summary

Op	transform(OpFilter opFilter, Op subOp)

Methods inherited from class com.hp.hpl.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

Methods inherited from class java.lang.Object

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

Constructor Detail

TransformFilterInequality

public TransformFilterInequality()

Creates a new transform

Method Detail

transform

public Op transform(OpFilter opFilter,
                    Op subOp)

Specified by:

transform in interface Transform

Overrides:

transform in class TransformCopy