/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.hp.hpl.jena.sparql.engine.index;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Set;
import com.hp.hpl.jena.graph.Node;
import com.hp.hpl.jena.sparql.algebra.Algebra;
import com.hp.hpl.jena.sparql.core.Var;
import com.hp.hpl.jena.sparql.engine.QueryIterator;
import com.hp.hpl.jena.sparql.engine.binding.Binding;
import com.hp.hpl.jena.sparql.engine.binding.BindingHashMap;
/**
* A slow "index" that looks for data by searching linearly through a set.
* Only used when the indexed data contains fewer bound variables than expected.
* Note that this class is only used for a MINUS operation that is removing data
* with potentially unbound values, and is therefore rarely used.
*
* TODO: If this index starts to be used more often then consider various options for
* indexing on the known bound variables.
* One possibility is for each variable (found in commonVars) to take
* the value of a var/value pair and TreeMap this to a set of Bindings that it occurs in.
* This would offer a reduced set to search, and set intersections may also work
* (intersections like this could be done on Binding reference equality rather than value).
* TreeMap is suggested here, since there would be commonVars.size() maps, which would take
* a lot of heap, particularly since performance of this class is only an issue when the
* data to search is significant.
* @author Paul Gearon
*/
public class LinearIndex implements IndexTable {
final Set<Var> commonVars ;
List<Binding> table = new ArrayList<Binding>() ;
public LinearIndex(Set<Var> commonVars, QueryIterator data)
{
this.commonVars = commonVars ;
while ( data.hasNext() )
table.add(data.next()) ;
data.close() ;
}
public LinearIndex(Set<Var> commonVars, QueryIterator data, Set<HashIndexTable.Key> loadedData, Map<Var,Integer> mappings)
{
this.commonVars = commonVars ;
for ( HashIndexTable.Key key: loadedData )
table.add(toBinding(key, mappings)) ;
while ( data.hasNext() )
table.add(data.next()) ;
data.close() ;
}
@Override
public boolean containsCompatibleWithSharedDomain(Binding bindingLeft)
{
if ( commonVars.size() == 0 )
return false ;
for ( Binding bindingRight: table )
{
if ( hasCommonVars(bindingLeft, bindingRight)
&& Algebra.compatible(bindingLeft, bindingRight) )
return true ;
}
return false ;
}
private boolean hasCommonVars(Binding left, Binding right)
{
for ( Var v: commonVars )
{
if ( left.contains(v) && right.contains(v) )
return true ;
}
return false;
}
static Binding toBinding(HashIndexTable.Key key, Map<Var,Integer> mappings)
{
Node[] values = key.getNodes() ;
BindingHashMap b = new BindingHashMap() ;
for (Map.Entry<Var,Integer> mapping: mappings.entrySet())
{
Node value = values[mapping.getValue()] ;
if ( value != null )
b.add(mapping.getKey(), value) ;
}
return b ;
}
}