com.bigdata.rdf.sparql.ast.optimizers

Class ASTEmptyGroupOptimizer

java.lang.Object

com.bigdata.rdf.sparql.ast.optimizers.ASTEmptyGroupOptimizer

All Implemented Interfaces:

IASTOptimizer

public class ASTEmptyGroupOptimizer
extends Object
implements IASTOptimizer

Eliminate semantically empty join group nodes which are the sole child of another join groups. Such nodes either do not specify a context or they specify the same context as the parent.

 { { ... } } => { ... }
 

and for non-graph groups:

 { ... {} } => { ... }
 

This is also done when the child is a UNION.

 { UNION {...} } => UNION {...}
 

Or

 { GRAPH ?g {...} } => GRAPH ?g {...}
 

Note: An empty {} matches a single empty solution. Since we always push in an empty solution and the join of anything with an empty solution is that source solution, this is the same as not running the group, so we just eliminate the empty group.

Version:

$Id: ASTEmptyGroupOptimizer.java 5177 2011-09-12 17:49:44Z thompsonbry $

Author:

Bryan Thompson

Constructor Summary

Constructors

Constructor and Description
ASTEmptyGroupOptimizer()

Method Summary

Methods

Modifier and Type	Method and Description
QueryNodeWithBindingSet	optimize(AST2BOpContext context, QueryNodeWithBindingSet input) Optimize the AST.

Methods inherited from class java.lang.Object

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

Constructor Detail

ASTEmptyGroupOptimizer

public ASTEmptyGroupOptimizer()

Method Detail

optimize

public QueryNodeWithBindingSet optimize(AST2BOpContext context,
                               QueryNodeWithBindingSet input)

Description copied from interface: IASTOptimizer

Optimize the AST.

Specified by:

optimize in interface IASTOptimizer

Parameters:

context - The evaluation context.

input - The input to the optimizer, consisting of a queryNode and input binding set.

Returns:

An instance of type QueryNodeWithBindingSet.