edu.stanford.nlp.trees.TreeNormalizer Maven / Gradle / Ivy
package edu.stanford.nlp.trees;
import java.io.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
*/
public class TreeNormalizer implements Serializable {
public TreeNormalizer() {
}
/**
* Normalizes a leaf contents (and maybe intern it).
*
* @param leaf The String that decorates the leaf
* @return The normalized form of this leaf String
*/
public String normalizeTerminal(String leaf) {
return leaf;
}
/**
* Normalizes a nonterminal contents (and maybe intern it).
*
* @param category The String that decorates this nonterminal node
* @return The normalized form of this nonterminal String
*/
public String normalizeNonterminal(String category) {
return category;
}
/**
* 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.
*
* @param tree The tree to be normalized
* @param tf the TreeFactory to create new nodes (if needed)
* @return Tree the normalized tree
*/
public Tree normalizeWholeTree(Tree tree, TreeFactory tf) {
return tree;
}
private static final long serialVersionUID = 1540681875853883387L;
}