it.unibz.inf.ontop.iq.optimizer

Class FlattenUnionOptimizer

java.lang.Object

it.unibz.inf.ontop.iq.optimizer.impl.NodeCentricDepthFirstOptimizer<FlattenUnionProposal>

it.unibz.inf.ontop.iq.optimizer.FlattenUnionOptimizer

All Implemented Interfaces:

IntermediateQueryOptimizer

public class FlattenUnionOptimizer
extends NodeCentricDepthFirstOptimizer<FlattenUnionProposal>

Flattens UnionNodes.

The algorithm searches the query q depth-first. If a UnionNode u1 is encountered, it proceeds as follows: .Retrieve the set U composed of u1, all children UnionNodes of u1, all children UnionNodes of these, etc. (recursively). .Retrieve the set C of all child subtrees of some node in U. .Within C, retain the set C' of subtrees whose root is not a UnionNode. .Build the subtree s, whose root is a union node projecting the same variables as u1, and such that the children subtrees of s are the subtrees in C'. .In q, replace the subtree rooted in u1 by s. .Continue the depth-first search

Assumption: the input query is well-formed wrt projections.

Constructor Summary

Constructors

Constructor and Description
FlattenUnionOptimizer()

Method Summary

Modifier and Type	Method and Description
protected Optional<FlattenUnionProposal>	evaluateNode(QueryNode node, IntermediateQuery query)
IntermediateQuery	optimize(IntermediateQuery query) TODO: explain

Methods inherited from class it.unibz.inf.ontop.iq.optimizer.impl.NodeCentricDepthFirstOptimizer

optimizeQuery

Methods inherited from class java.lang.Object

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

Constructor Detail

FlattenUnionOptimizer

public FlattenUnionOptimizer()

Method Detail

optimize

public IntermediateQuery optimize(IntermediateQuery query)
                           throws EmptyQueryException

Description copied from interface: IntermediateQueryOptimizer

TODO: explain

Specified by:

optimize in interface IntermediateQueryOptimizer

Overrides:

optimize in class NodeCentricDepthFirstOptimizer<FlattenUnionProposal>

Throws:

EmptyQueryException

evaluateNode

protected Optional<FlattenUnionProposal> evaluateNode(QueryNode node,
                                                      IntermediateQuery query)

Specified by:

evaluateNode in class NodeCentricDepthFirstOptimizer<FlattenUnionProposal>