/**
* Copyright (c) 2013, Institute of Information Systems (Sven Groppe and contributors of LUPOSDATE), University of Luebeck
*
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without modification, are permitted provided that the
* following conditions are met:
*
* - Redistributions of source code must retain the above copyright notice, this list of conditions and the following
* disclaimer.
* - Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the
* following disclaimer in the documentation and/or other materials provided with the distribution.
* - Neither the name of the University of Luebeck nor the names of its contributors may be used to endorse or promote
* products derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
* GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package lupos.distributed.query.operator.withouthistogramsubmission;
import java.util.Collection;
import java.util.Iterator;
import lupos.datastructures.bindings.Bindings;
import lupos.datastructures.items.Item;
import lupos.datastructures.items.Variable;
import lupos.datastructures.items.literal.Literal;
import lupos.datastructures.queryresult.IteratorQueryResult;
import lupos.datastructures.queryresult.QueryResult;
import lupos.distributed.query.operator.QueryClientIndices;
import lupos.engine.operators.OperatorIDTuple;
import lupos.engine.operators.index.BasicIndexScan;
import lupos.engine.operators.index.Indices;
import lupos.engine.operators.index.Root;
import lupos.engine.operators.tripleoperator.TriplePattern;
import lupos.misc.util.ImmutableIterator;
/**
* This class represents an index scan operator for the distributed query evaluators...
*/
public class QueryClientIndexScan extends BasicIndexScan {
public QueryClientIndexScan(final OperatorIDTuple succeedingOperator,
final Collection<TriplePattern> triplePatterns, final Item rdfGraph, final Root root) {
super(succeedingOperator, triplePatterns, rdfGraph, root);
}
public QueryClientIndexScan(final Root root, final Collection<TriplePattern> triplePatterns) {
super(root, triplePatterns);
}
@Override
public QueryResult join(final Indices indices, final Bindings bindings) {
// a fetch as needed distributed join strategy is implemented
final QueryClientIndices queryClientIndices = (QueryClientIndices) indices;
QueryResult result = QueryResult.createInstance();
result.add(bindings);
for (final TriplePattern pattern : this.triplePatterns) {
final QueryResult iResult = result;
result = QueryResult.createInstance();
for(final Bindings b: iResult){
final TriplePattern tpWithReplacedVariables = this.determineTriplePatternToEvaluate(pattern, b);
final QueryResult resultOfTP = queryClientIndices.evaluateTriplePattern(tpWithReplacedVariables);
if(resultOfTP!=null){
result.addAll(this.addBindings(b, resultOfTP));
}
}
}
return result;
}
/**
* Adds all bound values of variables in a given bindings to a query result
* @param bindings the given bindings
* @param queryResult the queryResult to be added with bindings
* @return the query result each bindings of which is added with the given bindings
*/
private IteratorQueryResult addBindings(final Bindings bindings, final QueryResult queryResult) {
return new IteratorQueryResult(new ImmutableIterator<Bindings>(){
Iterator<Bindings> it = queryResult.oneTimeIterator();
@Override
public boolean hasNext() {
return this.it.hasNext();
}
@Override
public Bindings next() {
if(this.it.hasNext()){
final Bindings b = this.it.next().clone();
b.addAll(bindings);
return b;
} else {
return null;
}
}
});
}
private TriplePattern determineTriplePatternToEvaluate(final TriplePattern pattern, final Bindings b) {
return new TriplePattern(this.getItem(pattern.getPos(0), b), this.getItem(pattern.getPos(1), b), this.getItem(pattern.getPos(2), b));
}
/**
* Replaces variables with their values in a given bindings, otherwise return the original literal.
* @param item the literal or variable
* @param bindings the intermediate solution
* @return the value in bindings if item is a variable and bound in bindings, otherwise just item
*/
private Item getItem(final Item item, final Bindings bindings){
if(item.isVariable()){
final Literal literal = bindings.get((Variable)item);
if(literal!=null){
return literal;
}
}
return item;
}
}