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## edu.stanford.nlp.trees
Class AbstractCollinsHeadFinder

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

All Implemented Interfaces:
  HeadFinder, Serializable

Direct Known Subclasses:
  ChineseHeadFinder, CollinsHeadFinder

    public abstract class AbstractCollinsHeadFinder

extends Object
implements HeadFinder

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 "leftexcept" means to take the first thing from the left that isn't in the list "rightexcept" means to take the first thing from the right that isn't on the list

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<String,String[][]>` | `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.
`Tree` | `determineHead(Tree t, Tree parent)` Determine which daughter of the current parse tree is the head.
`protected Tree` | `determineNonTrivialHead(Tree t, Tree parent)` Called by determineHead and may be overridden in subclasses if special treatment is necessary for particular categories.
`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<String,String[][]> 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`

### determineHead

    public Tree determineHead(Tree t,
                              Tree parent)

  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
    `parent` - The parent of t
  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,
                                           Tree parent)

  Called by determineHead and may be overridden in subclasses if special treatment is necessary for particular categories.

### 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

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