Package edu.stanford.nlp.trees

Class BobChrisTreeNormalizer

  • All Implemented Interfaces:
    TreeTransformer, Serializable, Function<Tree,​Tree>
    Direct Known Subclasses:
    ArabicTreeNormalizer, CharacterLevelTagExtender, CTBErrorCorrectingTreeNormalizer, FrenchTreeNormalizer, HebrewTreeNormalizer, NPTmpRetainingTreeNormalizer, SpanishTreeNormalizer
    public class BobChrisTreeNormalizer
extends TreeNormalizer
implements TreeTransformer
    Normalizes trees in the way used in Manning and Carpenter 1997. NB: This implementation is still incomplete! The normalizations performed are: (i) terminals are interned, (ii) nonterminals are stripped of alternants, functional tags and cross-reference codes, and then interned, (iii) empty elements (ones with nonterminal label "-NONE-") are deleted from the tree, (iv) the null label at the root node is replaced with the label "ROOT".
    17 Apr 2001: This was fixed to work with different kinds of labels, by making proper use of the Label interface, after it was moved into the trees module.

    The normalizations of the original (Prolog) BobChrisNormalize were: 1. Remap the root node to be called 'ROOT' 2. Truncate all nonterminal labels before characters introducing annotations according to TreebankLanguagePack (traditionally, -, =, | or # (last for BLLIP)) 3. Remap the representation of certain leaf symbols (brackets etc.) 4. Map to lowercase all leaf nodes 5. Delete empty/trace nodes (ones marked '-NONE-') 6. Recursively delete any nodes that do not dominate any words 7. Delete A over A nodes where the top A dominates nothing else 8. Remove backslashes from lexical items (the Treebank inserts them to escape slashes (/) and stars (*)). 4 is deliberately omitted, and a few things are purely aesthetic.

    14 June 2002: It now deletes unary A over A if both nodes' labels are equal (7), and (6) was always part of the Tree.prune() functionality... 30 June 2005: Also splice out an EDITED node, just in case you're parsing the Brown corpus.

    Author:
    Christopher Manning
    See Also:
    Serialized Form

    • Constructor Detail

      • BobChrisTreeNormalizer

        public BobChrisTreeNormalizer()

    • Method Detail

      • normalizeTerminal

        public String normalizeTerminal​(String leaf)
        Normalizes a leaf contents. This implementation interns the leaf.
        Overrides:
        normalizeTerminal in class TreeNormalizer
        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. This implementation strips functional tags, etc. and interns the nonterminal.
        Overrides:
        normalizeNonterminal in class TreeNormalizer
        Parameters:
        category - The String that decorates this nonterminal node
        Returns:
        The normalized form of this nonterminal String

      • cleanUpLabel

        protected String cleanUpLabel​(String label)
        Remove things like hyphened functional tags and equals from the end of a node label. This version always just returns the phrase structure category, or "ROOT" if the label was null.
        Parameters:
        label - The label from the treebank
        Returns:
        The cleaned up label (phrase structure category)

      • normalizeWholeTree

        public Tree normalizeWholeTree​(Tree tree,
                               TreeFactory tf)
        Normalize a whole tree -- one can assume that this is the root. This implementation deletes empty elements (ones with nonterminal tag label '-NONE-') from the tree, and splices out unary A over A nodes. It assumes that it is not given a null tree, but it may return one if there are no real words.
        Overrides:
        normalizeWholeTree in class TreeNormalizer
        Parameters:
        tree - The tree to be normalized
        tf - the TreeFactory to create new nodes (if needed)
        Returns:
        The normalized tree. May be null which means to not use this tree at all.

      • transformTree

        public Tree transformTree​(Tree tree)
        Description copied from interface: TreeTransformer
        Does whatever one needs to do to a particular tree. This routine is passed a whole Tree, and could itself work recursively, but the canonical usage is to invoke this method via the Tree.transform() method, which will apply the transformer in a bottom-up manner to each local Tree, and hence the implementation of TreeTransformer should merely examine and change a local (one-level) Tree.
        Specified by:
        transformTree in interface TreeTransformer
        Parameters:
        tree - A tree. Classes implementing this interface can assume that the tree passed in is not null.
        Returns:
        The transformed Tree