// Copyright (c) 2006 - 2008, Clark & Parsia, LLC. <http://www.clarkparsia.com>
// This source code is available under the terms of the Affero General Public
// License v3.
//
// Please see LICENSE.txt for full license terms, including the availability of
// proprietary exceptions.
// Questions, comments, or requests for clarification: licensing@clarkparsia.com
package com.clarkparsia.pellet.sparqldl.engine;
import java.util.List;
import java.util.Stack;
import java.util.logging.Level;
import java.util.logging.Logger;
import org.mindswap.pellet.exceptions.InternalReasonerException;
import org.mindswap.pellet.utils.SetUtils;
import com.clarkparsia.pellet.sparqldl.model.Query;
import com.clarkparsia.pellet.sparqldl.model.QueryAtom;
import com.clarkparsia.pellet.sparqldl.model.QueryPredicate;
import com.clarkparsia.pellet.sparqldl.model.ResultBinding;
/**
* <p>
* Title: Query Plan that recomputes the cost of the query in a greedy way.
* </p>
* <p>
* Description: TODO cache costs - not to recompute them
* </p>
* <p>
* Copyright: Copyright (c) 2007
* </p>
* <p>
* Company: Clark & Parsia, LLC. <http://www.clarkparsia.com>
* </p>
*
* @author Petr Kremen
*/
public class IncrementalQueryPlan extends QueryPlan {
private static final Logger log = Logger.getLogger( IncrementalQueryPlan.class.getName() );
public final Stack<Integer> explored;
private final List<QueryAtom> atoms;
private int size;
private QueryCost cost;
public IncrementalQueryPlan(Query query) {
super( query );
QuerySizeEstimator.computeSizeEstimate( query );
explored = new Stack<Integer>();
atoms = query.getAtoms();
size = atoms.size();
cost = new QueryCost( query.getKB() );
reset();
}
@Override
public QueryAtom next(final ResultBinding binding) {
int best = -1;
QueryAtom bestAtom = null;
double bestCost = Double.POSITIVE_INFINITY;
LOOP: for( int i = 0; i < size; i++ ) {
if( !explored.contains( i ) ) {
QueryAtom atom = atoms.get( i );
QueryAtom atom2 = atom.apply( binding );
if( atom2.getPredicate().equals( QueryPredicate.NotKnown ) && !atom2.isGround() ) {
for( int j = 0; j < atoms.size(); j++ ) {
if( i == j || explored.contains( j ) ) {
continue;
}
QueryAtom nextAtom = atoms.get( j );
if( SetUtils.intersects( nextAtom.getArguments(), atom2.getArguments() ) ) {
if( log.isLoggable( Level.FINE ) )
log.fine( "Unbound vars for not" );
continue LOOP;
}
}
}
final double atomCost = cost.estimate( atom2 );
if( log.isLoggable( Level.FINER ) ) {
log.finer( "Atom=" + atom + ", cost=" + cost + ", best cost=" + bestCost );
}
if( atomCost <= bestCost ) {
bestCost = atomCost;
bestAtom = atom2;
best = i;
}
}
}
if( best == -1 ) {
throw new InternalReasonerException( "Cannot find a valid atom in " + atoms
+ " where explored=" + explored );
}
explored.add( best );
if( log.isLoggable( Level.FINER ) ) {
StringBuffer indent = new StringBuffer();
for( int j = 0; j < explored.size(); j++ ) {
indent.append( " " );
}
String treePrint = indent.toString() + bestAtom + " : " + bestCost;
log.finer( treePrint );
}
return bestAtom;
}
@Override
public boolean hasNext() {
return explored.size() < size;
}
@Override
public void back() {
explored.pop();
}
@Override
public void reset() {
explored.clear();
}
}