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* Licensed to the Apache Software Foundation (ASF) under one
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* 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,
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* See the License for the specific language governing permissions and
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package com.hp.hpl.jena.sparql.algebra.optimize;
import com.hp.hpl.jena.sparql.algebra.Op ;
import com.hp.hpl.jena.sparql.algebra.TransformCopy ;
import com.hp.hpl.jena.sparql.algebra.op.OpPath ;
import com.hp.hpl.jena.sparql.core.PathBlock ;
import com.hp.hpl.jena.sparql.path.PathCompiler ;
import com.hp.hpl.jena.sparql.path.PathLib ;
/** Perform the equivalent of the trasnactions in the SPARQL 1.1 spec.
* ARQ regards path transformation as an optimization.
* ARQ does not execute the exact transformation as per spec as there are better ways to do it.
*/
public class TransformPathFlattern extends TransformCopy
{
// This transform is also used so programmtically built queries also get converted.
// Need previous BGP for merging? Do as a separate pass (sequence, BGP collapse)
private PathCompiler pathCompiler ;
public TransformPathFlattern() { this(new PathCompiler()) ; }
public TransformPathFlattern(PathCompiler pathCompiler)
{
this.pathCompiler = pathCompiler ;
}
@Override
public Op transform(OpPath opPath)
{
// Flatten down to triples where possible.
PathBlock pattern = pathCompiler.reduce(opPath.getTriplePath()) ;
// Any generated paths of exactly one to triple; convert to Op.
return PathLib.pathToTriples(pattern) ;
}
}