edu.stanford.nlp.trees

Class UniversalSemanticHeadFinder

java.lang.Object

edu.stanford.nlp.trees.AbstractCollinsHeadFinder

edu.stanford.nlp.trees.CollinsHeadFinder

edu.stanford.nlp.trees.ModCollinsHeadFinder

edu.stanford.nlp.trees.UniversalSemanticHeadFinder

All Implemented Interfaces:

CopulaHeadFinder, HeadFinder, java.io.Serializable

public class UniversalSemanticHeadFinder
extends ModCollinsHeadFinder

Implements a 'semantic head' variant of the the HeadFinder found in Michael Collins' 1999 thesis. This version chooses the semantic head verb rather than the verb form for cases with verbs. And it makes similar themed changes to other categories: e.g., in question phrases, like "Which Brazilian game", the head is made "game" not "Which" as in common PTB head rules.

By default the SemanticHeadFinder uses a treatment of copula where the complement of the copula is taken as the head. That is, a sentence like "Bill is big" will be analyzed as:

nsubj(big, Bill)
cop(big, is)

This analysis is used for questions and declaratives for adjective complements and declarative nominal complements. However Wh-sentences with nominal complements do not receive this treatment. "Who is the president?" is analyzed with "the president" as nsubj and "who" as "attr" of the copula:

nsubj(is, president)
attr(is, Who)

(Such nominal copula sentences are complex: arguably, depending on the circumstances, several analyses are possible, with either the overt NP able to be any of the subject, the predicate, or one of two referential entities connected by an equational copula. These uses aren't differentiated.)

Existential sentences are treated as follows:

"There is a man"
expl(is, There)
det(man-4, a-3)
nsubj(is-2, man-4)

Author:

John Rappaport, Marie-Catherine de Marneffe, Anna Rafferty, Sebastian Schuster

See Also:

Serialized Form

Field Summary

Fields inherited from class edu.stanford.nlp.trees.AbstractCollinsHeadFinder

defaultLeftRule, defaultRightRule, defaultRule, nonTerminalInfo, tlp

Constructor Summary

Constructors

Constructor and Description
UniversalSemanticHeadFinder()
UniversalSemanticHeadFinder(boolean noCopulaHead)
UniversalSemanticHeadFinder(TreebankLanguagePack tlp, boolean noCopulaHead) Create a SemanticHeadFinder.

Method Summary

Modifier and Type	Method and Description
protected Tree	determineNonTrivialHead(Tree t, Tree parent) Determine which daughter of the current parse tree is the head.
boolean	isVerbalAuxiliary(Tree t) Returns true if this tree is a preterminal that is a verbal auxiliary.
boolean	makesCopulaHead() Generally will be false, except for SemanticHeadFinder
protected int	postOperationFix(int headIdx, Tree[] daughterTrees) Overwrite the postOperationFix method.

Methods inherited from class edu.stanford.nlp.trees.CollinsHeadFinder

main

Methods inherited from class edu.stanford.nlp.trees.AbstractCollinsHeadFinder

determineHead, determineHead, findMarkedHead, traverseLocate

Methods inherited from class java.lang.Object

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

Constructor Detail

UniversalSemanticHeadFinder

public UniversalSemanticHeadFinder()

UniversalSemanticHeadFinder

public UniversalSemanticHeadFinder(boolean noCopulaHead)

UniversalSemanticHeadFinder

public UniversalSemanticHeadFinder(TreebankLanguagePack tlp,
                                   boolean noCopulaHead)

Create a SemanticHeadFinder.

Parameters:

tlp - The TreebankLanguagePack, used by the superclass to get basic category of constituents.

noCopulaHead - If true, a copular verb (a form of be) is not treated as head when it has an AdjP or NP complement. If false, a copula verb is still always treated as a head. But it will still be treated as an auxiliary in periphrastic tenses with a VP complement.

Method Detail

makesCopulaHead

public boolean makesCopulaHead()

Description copied from class: AbstractCollinsHeadFinder

Generally will be false, except for SemanticHeadFinder

Specified by:

makesCopulaHead in interface CopulaHeadFinder

Overrides:

makesCopulaHead in class AbstractCollinsHeadFinder

postOperationFix

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

Overwrite the postOperationFix method. For "a, b and c" or similar: we want "a" to be the head.

Overrides:

postOperationFix in class CollinsHeadFinder

Parameters:

headIdx - The index of the proposed head

daughterTrees - The array of daughter trees

Returns:

The new headIndex

determineNonTrivialHead

protected Tree determineNonTrivialHead(Tree t,
                                       Tree parent)

Determine which daughter of the current parse tree is the head. It assumes that the daughters already have had their heads determined. Uses special rule for VP heads

Overrides:

determineNonTrivialHead in class AbstractCollinsHeadFinder

Parameters:

t - The parse tree to examine the daughters of. This is assumed to never be a leaf

parent - The parent of t (or may be null)

Returns:

The parse tree that is the head

isVerbalAuxiliary

public boolean isVerbalAuxiliary(Tree t)

Returns true if this tree is a preterminal that is a verbal auxiliary.

Parameters:

t - A tree to examine for being an auxiliary.

Returns:

Whether it is a verbal auxiliary (be, do, have, get)