edu.umn.cs.nlp.parser
Class Grammar

java.lang.Object
  edu.umn.cs.nlp.parser.Grammar

All Implemented Interfaces:

GrammarInterface

public class Grammar
extends Object
implements GrammarInterface

Context-free grammar capable of parsing sentences using a variant of the CKY+ parsing algorithm.

Rules in this grammar are not required to be in Chomsky Normal Form (CNF).

This class uses a Berkeley DB Java Edition database to store the rules.

Version:

$LastChangedDate: 2007-07-24 16:48:53 -0500 (Tue, 24 Jul 2007) $

Author:

Lane Schwartz

Constructor Summary

Grammar(String databaseName, String databaseDirectory, boolean allowDuplicates)
Opens a grammar stored in the specified database.

Method Summary

void	addRule(BasicRuleLHS lhs, String... rhs) Add a new rule to the grammar.
void	close() Close the grammar.
static void	main(String[] args) Example usage of this class with a small sample grammar and test sentences.
ParseTree	parse(String... token) Attempts to parse the given series of tokens using this grammar.
ParseTree	parse(String sentence) Attempts to parse the given sentence using this grammar.
Collection<ParseTree>	parseAll(String... sentences) Attempts to parse each of the given sentences using parse(String sentence).
boolean	parses(String... token) Determines if the given series of tokens can be successfully parsed by this grammar.
boolean	parses(String sentence) Determines if the given sentence can be successfully parsed by this grammar.
void	setLocale(Locale locale) Sets the locale.

Methods inherited from class java.lang.Object

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

Constructor Detail

Grammar

public Grammar(String databaseName,
               String databaseDirectory,
               boolean allowDuplicates)

Opens a grammar stored in the specified database.

Parameters:

databaseName - the name of the rules database

databaseDirectory - the directory where the database file are stored - this directory must already exist

allowDuplicates - indicates whether duplicate rules are allowed in the specified database

Method Detail

close

public void close()

Close the grammar. This method closes the underlying database which backs the grammar. This method must be called to properly close the database. After this method is called, no further calls on this grammar object should be made.

addRule

public void addRule(BasicRuleLHS lhs,
                    String... rhs)

Add a new rule to the grammar.

Parameters:

lhs - The left-hand-side of the rule. Must be a non-terminal.

rhs - The right-hand-side children of the rule. Each rhs element may be a terminal or a non-terminal.

parse

public ParseTree parse(String sentence)

Attempts to parse the given sentence using this grammar. Uses a modified CKY+ parsing algorithm.

If the grammar produces more than one parse of the sentence, an arbitrary valid parse is returned.

Specified by:

parse in interface GrammarInterface

Parameters:

sentence - The sentence to be parsed. Will be lowercased using the default locale and then tokenized prior to parsing.

Returns:

a valid parse tree representing the most likely parse if this grammar can parse the given sentence; ParseTree.NULL_PARSE otherwise.

See Also:

setLocale(Locale)

parse

public ParseTree parse(String... token)

Attempts to parse the given series of tokens using this grammar. Uses a modified CKY+ parsing algorithm.

If the grammar produces more than one parse of the sentence, an arbitrary valid parse is returned.

Specified by:

parse in interface GrammarInterface

Parameters:

token - Array of tokens specifying the sentence to be parsed. No lowercasing will be performed by this method.

Returns:

a valid parse tree if this grammar can parse the given sentence; ParseTree.NULL_PARSE otherwise.

parseAll

public Collection<ParseTree> parseAll(String... sentences)

Attempts to parse each of the given sentences using parse(String sentence).

Specified by:

parseAll in interface GrammarInterface

Parameters:

sentences - the sentences to be parsed.

Returns:

one ParseTree per sentence

parses

public boolean parses(String sentence)

Determines if the given sentence can be successfully parsed by this grammar.

Specified by:

parses in interface GrammarInterface

Parameters:

sentence - The sentence to be parsed. Will be lowercased using the default locale and then tokenized prior to parsing.

Returns:

true if this grammar can parse the given sentence; false otherwise.

See Also:

setLocale(Locale)

parses

public boolean parses(String... token)

Determines if the given series of tokens can be successfully parsed by this grammar.

Specified by:

parses in interface GrammarInterface

Parameters:

token - Array of tokens specifying the sentence to be parsed. No lowercasing will be performed by this method.

Returns:

true if this grammar can parse the given sentence; false otherwise.

setLocale

public void setLocale(Locale locale)

Sets the locale. This will be used by parse(String sentence) and by parses(String sentence) when lowercasing the sentence.

Parameters:

locale - the locale to use when performing lowercasing

See Also:

String.toLowerCase(Locale)

main

public static void main(String[] args)

Example usage of this class with a small sample grammar and test sentences.

Parameters:

args - arguments are ignored