edu.stanford.nlp.trees
Class AbstractCollinsHeadFinder

java.lang.Object
  edu.stanford.nlp.trees.AbstractCollinsHeadFinder

All Implemented Interfaces:

HeadFinder, Serializable

Direct Known Subclasses:

BikelChineseHeadFinder, ChineseHeadFinder, CollinsHeadFinder, NegraHeadFinder, SunJurafskyChineseHeadFinder, TueBaDZHeadFinder

public abstract class AbstractCollinsHeadFinder
extends Object
implements HeadFinder, Serializable

A base class for Head Finders similar to the one described in Michael Collins' 1999 thesis. For a given constituent we perform

for categoryList in categoryLists for index = 1 to n [or n to 1 if R->L] for category in categoryList if category equals daughter[index] choose it.

with a final default that goes with the direction (L->R or R->L) For most constituents, there will be only one category in the list, the exception being, in Collins' original version, NP.

It is up to the overriding base class to initialize the map from constituent type to categoryLists, "nonTerminalInfo", in its constructor. Entries are presumed to be of type String[][]. Each String[] is a list of categories, except for the first entry, which specifies direction of traversal and must be one of "right", "left" or "rightdis" or "leftdis".

"left" means search left-to-right by category and then by position "leftdis" means search left-to-right by position and then by category "right" means search right-to-left by category and then by position "rightdis" means search right-to-left by position and then by category

10/28/2002 -- Category label identity checking now uses the equals() method instead of ==, so not interning category labels shouldn't break things anymore. (Roger Levy)
2003/02/10 -- Changed to use TreebankLanguagePack and to cut on characters that set off annotations, so this should work even if functional tags are still on nodes.
2004/03/30 -- Made abstract base class and subclasses for CollinsHeadFinder, ModCollinsHeadFinder, SemanticHeadFinder, ChineseHeadFinder (and trees.icegb.ICEGBHeadFinder, trees.international.negra.NegraHeadFinder, and movetrees.EnglishPennMaxProjectionHeadFinder)

Author:

Christopher Manning, Galen Andrew

See Also:

Serialized Form

Field Summary

protected String[]	defaultRule
protected HashMap	nonTerminalInfo
protected TreebankLanguagePack	tlp

Constructor Summary

protected

AbstractCollinsHeadFinder(TreebankLanguagePack tlp)

Method Summary

Tree	determineHead(Tree t) Determine which daughter of the current parse tree is the head.
protected Tree	determineNonTrivialHead(Tree t)
protected Tree	findMarkedHead(Tree t) A way for subclasses for corpora with explicit head markings to return the explicitly marked head
protected int	postOperationFix(int headIdx, Tree[] daughterTrees) A way for subclasses to fix any heads under special conditions The default does nothing.
protected Tree	traverseLocate(Tree[] daughterTrees, String[] how, boolean deflt) Attempt to locate head daughter tree from among daughters.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

tlp

protected final TreebankLanguagePack tlp

nonTerminalInfo

protected HashMap nonTerminalInfo

defaultRule

protected String[] defaultRule

Constructor Detail

AbstractCollinsHeadFinder

protected AbstractCollinsHeadFinder(TreebankLanguagePack tlp)

Method Detail

findMarkedHead

protected Tree findMarkedHead(Tree t)

A way for subclasses for corpora with explicit head markings to return the explicitly marked head

Parameters:

t - a tree to find the head of

Returns:

the marked head-- null if no marked head

determineHead

public Tree determineHead(Tree t)

Determine which daughter of the current parse tree is the head.

Specified by:

determineHead in interface HeadFinder

Parameters:

t - The parse tree to examine the daughters of. If this is a leaf, null is returned

Returns:

The daughter parse tree that is the head of t

See Also:

for a routine to call this and spread heads throughout a tree

determineNonTrivialHead

protected Tree determineNonTrivialHead(Tree t)

traverseLocate

protected Tree traverseLocate(Tree[] daughterTrees,
                              String[] how,
                              boolean deflt)

Attempt to locate head daughter tree from among daughters. Go through daughterTrees looking for things from a set found by looking up the motherkey specifier in a hash map, and if you do not find one, take leftmost or rightmost thing iff deflt is true, otherwise return null.

postOperationFix

protected int postOperationFix(int headIdx,
                               Tree[] daughterTrees)

A way for subclasses to fix any heads under special conditions The default does nothing.

Parameters:

headIdx - the index of the proposed head

daughterTrees - the array of daughter trees

Returns:

the new headIndex