src/joshua/decoder/segment_file/ConstraintRule.java

/*
 * This file is part of the Joshua Machine Translation System.
 * 
 * Joshua 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 library;
 * if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
 * 02111-1307 USA
 */
package joshua.decoder.segment_file;

import javax.swing.text.Segment;


/**
 * This interface is for an individual (partial) item to seed the chart with. All rules should be
 * flat (no hierarchical nonterminals).
 * <p>
 * The {@link Segment}, {@link ConstraintSpan}, and {@link ConstraintRule} interfaces are for
 * defining an interchange format between a SegmentFileParser and the Chart class. These interfaces
 * <emph>should not</emph> be used internally by the Chart. The objects returned by a
 * SegmentFileParser will not be optimal for use during decoding. The Chart should convert each of
 * these objects into its own internal representation during construction. That is the contract
 * described by these interfaces.
 * 
 * @see Type
 * 
 * @author wren ng thornton <wren@users.sourceforge.net>
 * @version $LastChangedDate: 2009-03-26 15:06:57 -0400 (Thu, 26 Mar 2009) $
 */
public interface ConstraintRule {

  /**
   * There are three types of ConstraintRule. The RULE type returns non-null values for all methods.
   * The LHS type provides a (non-null) value for the lhs method, but returns null for everything
   * else. And the RHS type provides a (non-null) value for nativeRhs and foreignRhs but returns
   * null for the lhs and features.
   * <p>
   * The interpretation of a RULE is that it adds a new rule to the grammar which only applies to
   * the associated span. If the associated span is hard, then the set of rules for that span will
   * override the regular grammar.
   * <p>
   * The intepretation of a LHS is that it provides a hard constraint that the associated span be
   * treated as the nonterminal for that span, thus filtering the regular grammar.
   * <p>
   * The interpretation of a RHS is that it provides a hard constraint to filter the regular grammar
   * such that only rules generating the desired translation can be used.
   */
  public enum Type {
    RULE, LHS, RHS
  };

  /** Return the type of this ConstraintRule. */
  Type type();


  /**
   * Return the left hand side of the constraint rule. If this is null, then this object is
   * specifying a translation for the span, but that translation may be derived from any
   * nonterminal. The nonterminal here must be one used by the regular grammar.
   */
  String lhs();


  /**
   * Return the native right hand side of the constraint rule. If this is null, then the regular
   * grammar will be used to fill in the derivation from the lhs.
   */
  String nativeRhs();


  /**
   * Return the foreign right hand side of the constraint rule. This must be consistent with the
   * sentence for the associated span, and is provided as a convenience method.
   */
  String foreignRhs();


  /**
   * Return the grammar feature values for the RULE. The length of this array must be the same as
   * for the regular grammar. We cannot enforce this requirement, but the
   * {@link joshua.decoder.chart_parser.Chart} must throw an error if there is a mismatch.
   */
  float[] features();
}