package edu.stanford.nlp.trees;
import java.io.Serializable;
/**
* 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.
*
* @param t The parse tree to examine the daughters of
* @return The daughter tree that is the head. This will always be
* non-null. An Exception will be thrown if no head can be determined.
* @throws IllegalStateException If a subclass has missing or badly
* formatted head rule data
* @throws IllegalArgumentException If the argument Tree has unexpected
* phrasal categories in it (and the implementation doesn't just use
* some heuristic to always determine some head).
*/
public Tree determineHead(Tree t);
/**
* Determine which daughter of the current parse tree is the head
* given the parent of the tree.
*
* @param t The parse tree to examine the daughters of
* @param parent The parent of tree t
* @return The daughter tree that is the head. This will always be
* non-null. An Exception will be thrown if no head can be determined.
*/
public Tree determineHead(Tree t, Tree parent);
}