edu.stanford.nlp.trees

Class TreeNormalizer

java.lang.Object

edu.stanford.nlp.trees.TreeNormalizer

All Implemented Interfaces:

Serializable

Direct Known Subclasses:

BobChrisTreeNormalizer, GrammaticalFunctionTreeNormalizer, NegraPennTreeNormalizer, OrderedCombinationTreeNormalizer, TueBaDZPennTreeNormalizer

public class TreeNormalizer
extends Object
implements Serializable

A class for tree normalization. The default one does no normalization. Other tree normalizers will change various node labels, or perhaps the whole tree geometry (by doing such things as deleting functional tags or empty elements). Another operation that a TreeNormalizer may wish to perform is interning the Strings passed to it. Can be reused as a Singleton. Designed to be extended.

The TreeNormalizer methods are in two groups. The contract for this class is that first normalizeTerminal or normalizeNonterminal will be called on each String that will be put into a Tree, when they are read from files or otherwise created. Then normalizeWholeTree will be called on the Tree. It normally walks the Tree making whatever modifications it wishes to. A TreeNormalizer need not make a deep copy of a Tree. It is assumed to be able to work destructively, because afterwards we will only use the normalized Tree.

Implementation note: This is a very old legacy class used in conjunction with PennTreeReader. It seems now that it would be better to move the String normalization into the tokenizer, and then we are just left with a (possibly destructive) TreeTransformer.

Author:

Christopher Manning

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
TreeNormalizer()

Method Summary

Modifier and Type	Method and Description
String	normalizeNonterminal(String category) Normalizes a nonterminal contents (and maybe intern it).
String	normalizeTerminal(String leaf) Normalizes a leaf contents (and maybe intern it).
Tree	normalizeWholeTree(Tree tree, TreeFactory tf) Normalize a whole tree -- this method assumes that the argument that it is passed is the root of a complete Tree.

Methods inherited from class java.lang.Object

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

Constructor Detail

TreeNormalizer

public TreeNormalizer()

Method Detail

normalizeTerminal

public String normalizeTerminal(String leaf)

Normalizes a leaf contents (and maybe intern it).

Parameters:

leaf - The String that decorates the leaf

Returns:

The normalized form of this leaf String

normalizeNonterminal

public String normalizeNonterminal(String category)

Normalizes a nonterminal contents (and maybe intern it).

Parameters:

category - The String that decorates this nonterminal node

Returns:

The normalized form of this nonterminal String

normalizeWholeTree

public Tree normalizeWholeTree(Tree tree,
                               TreeFactory tf)

Normalize a whole tree -- this method assumes that the argument that it is passed is the root of a complete Tree. It is normally implemented as a Tree-walking routine.

This method may return null. This is interpreted to mean that this is a tree that should not be included in further processing. PennTreeReader recognizes this return value, and asks for another Tree from the input Reader.

Parameters:

tree - The tree to be normalized

tf - the TreeFactory to create new nodes (if needed)

Returns:

Tree the normalized tree