QueryExecutor.java

/******************************************************************************* 
 * Copyright (c) 2004, 2007 IBM Corporation and Cambridge Semantics Incorporated.
 * All rights reserved. This program and the accompanying materials 
 * are made available under the terms of the Eclipse Public License v1.0 
 * which accompanies this distribution, and is available at 
 * http://www.eclipse.org/legal/epl-v10.html 
 * 
 * File: $Source: /cvsroot/slrp/glitter/com.ibm.adtech.glitter/src/com/ibm/adtech/glitter/query/QueryExecutor.java,v $
 * Created by:  Lee Feigenbaum (<a href="mailto:feigenbl@us.ibm.com">feigenbl@us.ibm.com</a>) 
 * Created on: 10/23/06
 * Revision: $Id: QueryExecutor.java 164 2007-07-31 14:11:09Z mroy $
 * 
 * Contributors: IBM Corporation - initial API and implementation 
 *     Cambridge Semantics Incorporated - Fork to Anzo
 *******************************************************************************/
package org.openanzo.glitter.query;

import org.openanzo.glitter.EngineConfig;
import org.openanzo.glitter.dataset.QueryDataset;
import org.openanzo.glitter.exception.GlitterException;

/**
 * A {@link QueryExecutor} implements the actual logic for orchestrating a {@link QueryController}, a {@link SolutionGenerator}, an {@link QueryDataset}, a
 * {@link QueryExecutionPlan}, and other components to produce a result set.
 * 
 * @author lee <lee@cambridgesemantics.com>
 * 
 */
public interface QueryExecutor {
    /**
     * Initialize the executor with information on the query.
     * 
     * @param config
     *            The engine configuration in effect.
     * @param controller
     *            The query controller with information on the parsed and prepared query.
     * @param sg
     *            The backend solution generator.
     * @param plan
     *            The query execution plan.
     */
    public abstract void initialize(EngineConfig config, QueryController controller, SolutionGenerator sg, QueryExecutionPlan plan);

    /**
     * Executes the query, returning a result set.
     * 
     * @return A {@link SolutionSet} with the bindings from executing the query against an {@link RDFDataset}.
     * @throws GlitterException
     */
    public abstract SolutionSet executeQuery() throws GlitterException;

    /**
     * Clients of an executor need to know whether the executor had a handle in putting together results, to know if reordering might be necessary. Executors
     * are considered trustworthy, while backends may not be.
     * 
     * @return true if results were composed from pieces provided by a backend; false if all results were generated by the backend.
     */
    public abstract boolean composedSolutions();
}