/*
* $Header$
* $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.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
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* 1. Redistributions of source code must retain the above copyright
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* 2. Redistributions in binary form must reproduce the above copyright
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* 3. The end-user documentation included with the redistribution, if
* any, must include the following acknowlegement:
* "This product includes software developed by the
* the JRDF Project (http://jrdf.sf.net/)."
* Alternately, this acknowlegement may appear in the software itself,
* if and wherever such third-party acknowlegements normally appear.
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* 4. The names "The JRDF Project" and "JRDF" must not be used to endorse
* or promote products derived from this software without prior written
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* 5. Products derived from this software may not be called "JRDF"
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* ====================================================================
*
* This software consists of voluntary contributions made by many
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* information on JRDF, please see <http://jrdf.sourceforge.net/>.
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package org.jrdf.query.relation.operation.mem.join.natural;
import org.jrdf.graph.Node;
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.mem.RelationHelper;
import org.jrdf.query.relation.operation.mem.join.TupleEngine;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import java.util.SortedSet;
/**
* Combines two relations attributes if they have common tuple values. The same as AND in Algebra A.
* <p/>
* The general algorithm is:
* 1. Find all matching attributes on two relations.
* 2. Union the attributes and tuples together.
* 3. Remove any attributes that are not common between the two.
* <p/>
*/
public class NaturalJoinEngine implements TupleEngine {
protected final TupleFactory tupleFactory;
protected final RelationHelper relationHelper;
public NaturalJoinEngine(TupleFactory newTupleFactory, RelationHelper newRelationHelper) {
this.tupleFactory = newTupleFactory;
this.relationHelper = newRelationHelper;
}
public SortedSet<Attribute> getHeading(EvaluatedRelation relation1, EvaluatedRelation relation2) {
return relationHelper.getHeadingUnions(relation1, relation2);
}
public void processRelations(SortedSet<Attribute> headings, EvaluatedRelation relation1,
EvaluatedRelation relation2, SortedSet<Tuple> result) {
Set<Tuple> tuples1 = relation1.getTuples();
Set<Tuple> tuples2 = relation2.getTuples();
if (tuples1.size() < tuples2.size()) {
startDoubleLoopProcessing(headings, tuples1, tuples2, result);
} else {
startDoubleLoopProcessing(headings, tuples2, tuples1, result);
}
}
private void startDoubleLoopProcessing(SortedSet<Attribute> headings, Set<Tuple> tuples1, Set<Tuple> tuples2,
SortedSet<Tuple> result) {
for (final Tuple tuple1 : tuples1) {
for (final Tuple tuple2 : tuples2) {
process(headings, result, tuple1, tuple2);
}
}
}
private void process(SortedSet<Attribute> headings, SortedSet<Tuple> result, Tuple tuple1, Tuple tuple2) {
Map<Attribute, Node> resultantAttributeValues = new HashMap<Attribute, Node>();
final boolean contradiction = relationHelper.addTuplesIfEqual(headings, tuple1, tuple2,
resultantAttributeValues);
// Only add results if we have found more items to add and there wasn't a contradiction in bound values.
if (!contradiction && !resultantAttributeValues.isEmpty()) {
final Tuple t = tupleFactory.getTuple(resultantAttributeValues);
result.add(t);
}
}
}