edu.stanford.nlp.trees
Class GrammaticalRelation

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

public class GrammaticalRelation
extends Object

GrammaticalRelation is used to define a standardized, hierarchical set of grammatical relations, together with patterns for identifying them in parse trees.

Each GrammaticalRelation has:

• a String short name, which should be a lowercase abbreviation of some kind,
• a String long name, which should be descriptive,
• a parent in the GrammaticalRelation hierarchy,
• a Pattern called sourcePattern which matches nodes from which this GrammaticalRelation could hold, and
• a list of zero or more TregexPatterns called targetPatterns, which describe the local tree structure which must hold between the source node and a target node for the GrammaticalRelation to apply.

The targetPatterns associated with a GrammaticalRelation are designed as follows. In order to recognize a grammatical relation X holding between nodes A and B in a parse tree, we want to associate with GrammaticalRelation X a TregexPattern such that:

• the root of the pattern matches A, and
• the pattern includes a special node label, "target", which matches B.

For example, for the grammatical relation PREDICATE which holds between a clause and its primary verb phrase, we might want to use the pattern "S < VP=target", in which the root will match a clause and the node labeled "target" will match the verb phrase.

For a given grammatical relation, the method getRelatedNodes() takes a Tree node as an argument and attempts to return other nodes which have this grammatical relation to the argument node. By default, this method operates as follows: it steps through the patterns in the pattern list, trying to match each pattern against the argument node, until it finds some matches. If a pattern matches, all matching nodes (that is, each node which corresponds to node label "target" in some match) are returned as a list; otherwise the next pattern is tried.

For some grammatical relations, we need more sophisticated logic to identify related nodes. In such cases, getRelatedNodes() can be overridden on a per-relation basis using anonymous subclassing.

Author:

Bill MacCartney, Galen Andrew (refactoring English-specific stuff)

See Also:

GrammaticalStructure, EnglishGrammaticalRelations, EnglishGrammaticalStructure

Field Summary

static GrammaticalRelation	DEPENDENT The "dependent" grammatical relation, which is the inverse of "governor".
static GrammaticalRelation	GOVERNOR The "governor" grammatical relation, which is the inverse of "dependent".

Constructor Summary

GrammaticalRelation(String shortName, String longName, GrammaticalRelation parent, String sourcePattern, String[] targetPatterns)

Method Summary

Collection<Tree>	getRelatedNodes(Tree t) Given a Tree node t, attempts to return a list of nodes to which node t has this grammatical relation.
boolean	isAncestor(GrammaticalRelation gr)
boolean	isApplicable(Tree t) Returns true iff the value of Tree node t matches the sourcePattern for this GrammaticalRelation, indicating that this GrammaticalRelation is one that could hold between Tree node t and some other node.
String	toPrettyString() Returns a String representation of this GrammaticalRelation and the hierarchy below it, with one node per line, indented according to level.
String	toString() Returns short name (abbreviation) for this GrammaticalRelation.

Methods inherited from class java.lang.Object

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

Field Detail

GOVERNOR

public static final GrammaticalRelation GOVERNOR

The "governor" grammatical relation, which is the inverse of "dependent".

Example: "the red car" → gov(red, car)

DEPENDENT

public static final GrammaticalRelation DEPENDENT

The "dependent" grammatical relation, which is the inverse of "governor".

Example: "the red car" → dep(car, red)

Constructor Detail

GrammaticalRelation

public GrammaticalRelation(String shortName,
                           String longName,
                           GrammaticalRelation parent,
                           String sourcePattern,
                           String[] targetPatterns)

Method Detail

getRelatedNodes

public Collection<Tree> getRelatedNodes(Tree t)

Given a Tree node t, attempts to return a list of nodes to which node t has this grammatical relation.

isApplicable

public boolean isApplicable(Tree t)

Returns true iff the value of Tree node t matches the sourcePattern for this GrammaticalRelation, indicating that this GrammaticalRelation is one that could hold between Tree node t and some other node.

isAncestor

public boolean isAncestor(GrammaticalRelation gr)

toString

public String toString()

Returns short name (abbreviation) for this GrammaticalRelation.

Overrides:

toString in class Object

toPrettyString

public String toPrettyString()

Returns a String representation of this GrammaticalRelation and the hierarchy below it, with one node per line, indented according to level.

Returns:

String representation of this GrammaticalRelation