abstracttermexpander.java

MG4J (Managing Gigabytes for Java) is a free full-text search engine for large document collections

package it.unimi.dsi.mg4j.query.nodes;

/*		 
 * MG4J: Managing Gigabytes for Java
 *
 * Copyright (C) 2006-2007 Sebastiano Vigna 
 *
 *  This library is free software; you can redistribute it and/or modify it
 *  under the terms of the GNU Lesser General Public License as published by the Free
 *  Software Foundation; either version 2.1 of the License, or (at your option)
 *  any later version.
 *
 *  This library is distributed in the hope that it will be useful, but
 *  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 *  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
 *  for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 */

/** A {@linkplain QueryTransformer query transformer} that just requires
 * implementing a method that {@linkplain #expand(Term) expands terms} (e.g., into
 * disjunctive queries).
 * 
 */

public abstract class AbstractTermExpander implements QueryTransformer {
	
	protected class ExpanderVisitor implements QueryBuilderVisitor<Query> {

		public QueryBuilderVisitor<Query> copy() {
			// TODO Auto-generated method stub
			return null;
		}

		public Query[] newArray( int len ) {
			return new Query[ len ];
		}

		public QueryBuilderVisitor<Query> prepare() { return this; }

		public Query visit( Term node ) throws QueryBuilderVisitorException {
			return expand( node );
		}

		public Query visit( Prefix node ) throws QueryBuilderVisitorException {
			return expand( node );
		}

		public Query visit( Range node ) throws QueryBuilderVisitorException {
			return node;
		}

		public Query visitPost( And node, Query[] subNode ) throws QueryBuilderVisitorException {
			return new And( subNode );
		}

		public Query visitPost( Consecutive node, Query[] subNode ) throws QueryBuilderVisitorException {
			return new Consecutive( subNode );
		}

		public Query visitPost( LowPass node, Query subNode ) throws QueryBuilderVisitorException {
			return new LowPass( subNode, node.k );
		}

		public Query visitPost( Not node, Query subNode ) throws QueryBuilderVisitorException {
			return new Not( subNode );
		}

		public Query visitPost( Or node, Query[] subNode ) throws QueryBuilderVisitorException {
			return new Or( subNode );
		}

		public Query visitPost( OrderedAnd node, Query[] subNode ) throws QueryBuilderVisitorException {
			return new OrderedAnd( subNode );
		}

		public Query visitPost( Align node, Query[] subNode ) throws QueryBuilderVisitorException {
			return new Align( subNode[ 0 ], subNode[ 1 ] );
		}

		public Query visitPost( Difference node, Query[] subNode ) throws QueryBuilderVisitorException {
			return new Difference( subNode[ 0 ], subNode[ 1 ] );
		}

		public Query visitPost( MultiTerm node, Query[] subNode ) throws QueryBuilderVisitorException {
			// TODO: is this semantics sensible?
			return new Or( subNode );
		}

		public Query visitPost( Select node, Query subNode ) throws QueryBuilderVisitorException {
			return new Select( node.index, subNode );
		}

		public boolean visitPre( And node ) throws QueryBuilderVisitorException {
			return true;
		}

		public boolean visitPre( Consecutive node ) throws QueryBuilderVisitorException {
			return true;
		}

		public boolean visitPre( LowPass node ) throws QueryBuilderVisitorException {
			return true;
		}

		public boolean visitPre( Not node ) throws QueryBuilderVisitorException {
			return true;
		}

		public boolean visitPre( Or node ) throws QueryBuilderVisitorException {
			return true;
		}

		public boolean visitPre( OrderedAnd node ) throws QueryBuilderVisitorException {
			return true;
		}

		public boolean visitPre( Align node ) throws QueryBuilderVisitorException {
			return true;
		}

		public boolean visitPre( Difference node ) throws QueryBuilderVisitorException {
			return true;
		}

		public boolean visitPre( MultiTerm node ) throws QueryBuilderVisitorException {
			return true;
		}

		public boolean visitPre( Select node ) throws QueryBuilderVisitorException {
			return true;
		}
		
	}
	
	/** The visitor used by this expander. */
	final private ExpanderVisitor expanderVisitor = new ExpanderVisitor();
	
	public Query transform( final Query query ) {
		try {
			return query.accept( expanderVisitor );
		}
		catch ( QueryBuilderVisitorException e ) {
			throw new RuntimeException( e );
		}
	}
	
	/** Expands a single term. 
	 * 
	 * @param term a term to be expanded.
	 * @return the resulting query.
	 */
	public abstract Query expand( Term term );
	
	/** Expands a prefix. 
	 * 
	 * @param prefix the prefix to be expanded.
	 * @return the resulting query.
	 */
	public abstract Query expand( Prefix prefix );
}