/*
* $Header$
* $Revision: 982 $
* $Date: 2006-12-08 18:42:51 +1000 (Fri, 08 Dec 2006) $
*
* ====================================================================
*
* The Apache Software License, Version 1.1
*
* Copyright (c) 2003-2009 The JRDF Project. All rights reserved.
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* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
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* any, must include the following acknowlegement:
* "This product includes software developed by the
* the JRDF Project (http://jrdf.sf.net/)."
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* This software consists of voluntary contributions made by many
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package org.jrdf.query.relation.operation.mem.join.semi;
import org.jrdf.graph.Node;
import org.jrdf.graph.NodeComparator;
import org.jrdf.query.relation.Attribute;
import org.jrdf.query.relation.EvaluatedRelation;
import org.jrdf.query.relation.Tuple;
import org.jrdf.query.relation.TupleFactory;
import org.jrdf.query.relation.constants.NullaryNode;
import org.jrdf.query.relation.operation.mem.join.TupleEngine;
import java.util.HashMap;
import java.util.Map;
import java.util.SortedSet;
/**
* Join two relations if they have common tuple values and projects the results back onto the first relation.
*/
// TODO AN AVP Refactoing - can some of this use RelationHelper?
// TODO Tuple Refactor.
public class SemiJoinEngine implements TupleEngine {
private final TupleFactory tupleFactory;
private final NodeComparator nodeComparator;
public SemiJoinEngine(TupleFactory newTupleFactory, NodeComparator newNodeComparator) {
this.tupleFactory = newTupleFactory;
this.nodeComparator = newNodeComparator;
}
public SortedSet<Attribute> getHeading(EvaluatedRelation relation1, EvaluatedRelation relation2) {
return relation1.getSortedHeading();
}
public void processRelations(SortedSet<Attribute> headings, EvaluatedRelation relation1,
EvaluatedRelation relation2, SortedSet<Tuple> result) {
for (Tuple tuple1 : relation1.getTuples()) {
for (Tuple tuple2 : relation2.getTuples()) {
process(headings, result, tuple1, tuple2);
}
}
}
private void process(SortedSet<Attribute> headings, SortedSet<Tuple> result, Tuple tuple1, Tuple tuple2) {
Map<Attribute, Node> allAttributeValuePairs = new HashMap<Attribute, Node>();
Map<Attribute, Node> lhsAttributeValuePairs = new HashMap<Attribute, Node>();
boolean contradiction = false;
for (Attribute attribute : headings) {
Node avp1 = tuple1.getValue(attribute);
Node avp2 = tuple2.getValue(attribute);
contradiction = addAttributeValuePair(attribute, avp1, avp2, allAttributeValuePairs,
lhsAttributeValuePairs);
// If we didn't find one for the current heading end early.
if (contradiction) {
break;
}
}
// Only add results if they are the same size
if ((!allAttributeValuePairs.isEmpty() && !contradiction)) {
Tuple t = tupleFactory.getTuple(lhsAttributeValuePairs);
result.add(t);
}
}
private boolean addAttributeValuePair(Attribute attribute, Node avp1, Node avp2,
Map<Attribute, Node> resultantAttributeValues,
Map<Attribute, Node> lhsAttributeValuePairs) {
// Add if avp1 is not null and avp2 is or they are both equal.
if (avp1 != null) {
return avp1NotNull(attribute, avp2, avp1, resultantAttributeValues, lhsAttributeValuePairs);
} else {
// Add if avp1 is null and avp2 is not.
return avp1Null(attribute, avp2, resultantAttributeValues, lhsAttributeValuePairs);
}
}
private boolean avp1NotNull(Attribute attribute, Node avp2, Node avp1,
Map<Attribute, Node> resultantAttributeValues,
Map<Attribute, Node> lhsAttributeValuePairs) {
if (avp2 == null) {
addResults(attribute, avp1, resultantAttributeValues, lhsAttributeValuePairs);
return false;
} else if (nodeComparator.compare(avp1, avp2) == 0) {
addNonNullaryAvp(attribute, avp1, avp2, resultantAttributeValues, lhsAttributeValuePairs);
return false;
} else {
return true;
}
}
private boolean avp1Null(Attribute attribute, Node avp2,
Map<Attribute, Node> resultantAttributeValues,
Map<Attribute, Node> lhsAttributeValuePairs) {
if (avp2 != null) {
addResults(attribute, avp2, resultantAttributeValues, lhsAttributeValuePairs);
}
return false;
}
private void addNonNullaryAvp(Attribute attribute, Node avp1, Node avp2,
Map<Attribute, Node> resultantAttributeValues,
Map<Attribute, Node> lhsAttributeValuePairs) {
if (!(avp1 instanceof NullaryNode)) {
addResults(attribute, avp1, resultantAttributeValues, lhsAttributeValuePairs);
} else {
addResults(attribute, avp2, resultantAttributeValues, lhsAttributeValuePairs);
}
}
private void addResults(Attribute attribute, Node avp,
Map<Attribute, Node> resultantAttributeValues,
Map<Attribute, Node> lhsAttributeValuePairs) {
resultantAttributeValues.put(attribute, avp);
lhsAttributeValuePairs.put(attribute, avp);
}
}