/*
* (c) Copyright 2007, 2008, 2009 Hewlett-Packard Development Company, LP
* All rights reserved.
* [See end of file]
*/
package arq.examples.engine;
import com.hp.hpl.jena.query.Query ;
import com.hp.hpl.jena.sparql.ARQInternalErrorException ;
import com.hp.hpl.jena.sparql.algebra.Op ;
import com.hp.hpl.jena.sparql.algebra.Transform ;
import com.hp.hpl.jena.sparql.algebra.TransformCopy ;
import com.hp.hpl.jena.sparql.algebra.Transformer ;
import com.hp.hpl.jena.sparql.algebra.op.OpBGP ;
import com.hp.hpl.jena.sparql.core.DatasetGraph ;
import com.hp.hpl.jena.sparql.engine.Plan ;
import com.hp.hpl.jena.sparql.engine.QueryEngineFactory ;
import com.hp.hpl.jena.sparql.engine.QueryEngineRegistry ;
import com.hp.hpl.jena.sparql.engine.QueryIterator ;
import com.hp.hpl.jena.sparql.engine.binding.Binding ;
import com.hp.hpl.jena.sparql.engine.main.QueryEngineMain ;
import com.hp.hpl.jena.sparql.util.Context ;
/** Example skeleton for a query engine.
* To just extend ARQ by custom basic graph pattern matching (a very common case)
* see the arq.examples.bgpmatching package.
* To take full control of query execution, use this example for catching the
* execution setup and see opexec for a customized OpExecutor for query execution.
*/
public class MyQueryEngine extends QueryEngineMain
{
// Do nothing template for a query engine.
public MyQueryEngine(Query query, DatasetGraph dataset, Binding initial, Context context)
{
super(query, dataset, initial, context) ;
}
public MyQueryEngine(Query query, DatasetGraph dataset)
{
// This will default to the global context with no initial settings
this(query, dataset, null, null) ;
}
@Override
public QueryIterator eval(Op op, DatasetGraph dsg, Binding initial, Context context)
{
// Extension point: access possible to all the parameters for execution.
// Be careful to deal with initial bindings.
Transform transform = new MyTransform() ;
op = Transformer.transform(transform, op) ;
return super.eval(op, dsg, initial, context) ;
}
@Override
protected Op modifyOp(Op op)
{
// Extension point: possible place to alter the algebra expression.
// Alternative to eval().
op = super.modifyOp(op) ;
// op = Algebra.toQuadForm(op) ;
return op ;
}
// ---- Registration of the factory for this query engine class.
// Query engine factory.
// Call MyQueryEngine.register() to add to the global query engine registry.
static QueryEngineFactory factory = new MyQueryEngineFactory() ;
static public QueryEngineFactory getFactory() { return factory ; }
static public void register() { QueryEngineRegistry.addFactory(factory) ; }
static public void unregister() { QueryEngineRegistry.removeFactory(factory) ; }
static class MyTransform extends TransformCopy
{
// Example, do nothing tranform.
@Override
public Op transform(OpBGP opBGP) { return opBGP ; }
}
static class MyQueryEngineFactory implements QueryEngineFactory
{
// Accept any dataset for query execution
public boolean accept(Query query, DatasetGraph dataset, Context context)
{ return true ; }
public Plan create(Query query, DatasetGraph dataset, Binding initial, Context context)
{
// Create a query engine instance.
MyQueryEngine engine = new MyQueryEngine(query, dataset, initial, context) ;
return engine.getPlan() ;
}
public boolean accept(Op op, DatasetGraph dataset, Context context)
{ // Refuse to accept algebra expressions directly.
return false ;
}
public Plan create(Op op, DatasetGraph dataset, Binding inputBinding, Context context)
{ // Shodul notbe called because acceept/Op is false
throw new ARQInternalErrorException("MyQueryEngine: factory calleddirectly with an algebra expression") ;
}
}
}
/*
* (c) Copyright 2007, 2008, 2009 Hewlett-Packard Development Company, LP
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. 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.
* 3. The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
*/