com.bigdata.rdf.sparql.ast.optimizers

Class ASTDescribeOptimizer

java.lang.Object

com.bigdata.rdf.sparql.ast.optimizers.ASTDescribeOptimizer

All Implemented Interfaces:

IASTOptimizer

public class ASTDescribeOptimizer
extends Object
implements IASTOptimizer

This optimizer rewrites the projection node of a DESCRIBE query into, generating a CONSTRUCT clause and extending the WHERE clause to capture the semantics of the DESCRIBE query. The query type is also changed to CONSTRUCT.

For example, the optimizer changes this:

 describe term1 term2 ...
 where {
    whereClause ...
 }
 

Into this:

 construct {
   term1 ?p1a ?o1 .
   ?s1   ?p1b term1 .
   term2 ?p2a ?o2 .
   ?s2   ?p2b term2 .
 }
 where {
   whereClause ...
   {
     term1 ?p1a ?o1 .
   } union {
     ?s1   ?p1b term1 .
   } union {
     term2 ?p2a ?o2 .
   } union {
     ?s2   ?p2b term2 .
   }
 

Note: The ASTConstructOptimizer will add a ProjectionNode based on the generated CONSTRUCT template.

See Also:

Concise Bounded Description

Constructor Summary

Constructors

Constructor and Description
ASTDescribeOptimizer()

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

ASTDescribeOptimizer

public ASTDescribeOptimizer()

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.