org.openanzo.glitter.query.rewriter
Class ConjunctiveRewriter

java.lang.Object
  org.openanzo.glitter.query.rewriter.ConjunctiveRewriter

All Implemented Interfaces:

TreeRewriter

public class ConjunctiveRewriter
extends java.lang.Object
implements TreeRewriter

The ConjunctiveRewriter takes advantage of the following equalities: { t1 t2 { t3 } } = t1 t2 t3 That is, triples within a single BGP are conjoined, as are GraphPatterns within a group. By flattening out nested groups and then merging multiple BGPs within a group, we take a great deal of complexity out of the AST and enable other query-plan optimizations. This also conjoins multiple filtered basic graph patterns. (Note that on the surface {t1 {t2} } is not identical to {t1 t2} because the two triples have different blank node scopes. At this point (the AST rewriting point), distinct blank nodes for identical labels in different scopes have already be created, so we can lose that difference.) (Note also that this equivalence might not hold for entaiments other than simple entailment, and as such a backend that implements other entailments should be wary in its use of the ConjunctiveRewriter.) ConjunctiveRewriter only operates on Group nodes, and only manipulates Group, BGP, and Filter nodes. TODO @@ ConjunctiveRewriter also needs to ensure that every Group has a BGP. TODO @@ This could be improved to flatten single element groups regardless of filters in children { { ?s ?p ?o. FILTER (...) } }.

Author:

Lee

Constructor Summary

ConjunctiveRewriter()

Method Summary

TreeNode

rewriteTreeNode(TreeNode node) Rewrites the given node from a SPARQL abstract syntax tree.

Methods inherited from class java.lang.Object

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

Constructor Detail

ConjunctiveRewriter

public ConjunctiveRewriter()

Method Detail

rewriteTreeNode

public TreeNode rewriteTreeNode(TreeNode node)

Description copied from interface: TreeRewriter

Rewrites the given node from a SPARQL abstract syntax tree.

Specified by:

rewriteTreeNode in interface TreeRewriter

Parameters:

node - the node in question

Returns:

A tree node to replace the passed in tree node. Returning node leaves this spot in the AST unchanged. Returning null removes this node from the tree. (Note that it is possible that removing the node will leave the tree in an invalid state. Behavior in this case is undefined.)