edu.berkeley.nlp.ling.HeadFinder Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of berkeleyparser Show documentation

The Berkeley parser analyzes the grammatical structure of natural language using probabilistic context-free grammars (PCFGs).

The newest version!

package edu.berkeley.nlp.ling;

import java.io.Serializable;

import edu.berkeley.nlp.syntax.Tree;
import edu.berkeley.nlp.util.Pair;

/**
 * An interface for finding the "head" daughter of a phrase structure tree.
 * This could potentially be any sense of "head", but has mainly been used
 * to find the lexical head for lexicalized PCFG parsing.
 *
 * @author Christopher Manning
 */
public interface HeadFinder extends Serializable {

  /**
   * Determine which daughter of the current parse tree is the head.
   * It assumes that the daughters already have had their heads
   * determined. Another method has to do the tree walking.
   *
   * @param t The parse tree to examine the daughters of
   * @return The parse tree that is the head.  The convention has been
   *         that this returns null if no head is found.
   *         But maybe it should throw an exception?
   */
  public Tree determineHead(Tree t);

  public static class Utils {

	public static Pair getHeadWordAndPartOfSpeechPair(HeadFinder hf, Tree tree) {
		String headWord = null;
		String headPOS = null;
		while (true) {
			if (tree.isPreTerminal()) {
				headPOS = tree.getLabel();
			}
			if (tree.isLeaf()) {
				headWord = tree.getLabel();
				break;
			}
			tree = hf.determineHead(tree);
		}
		return Pair.newPair(headWord, headPOS);
	}

  }

}