RegexpTagger.java

package edu.northwestern.at.utils.corpuslinguistics.postagger.regexp;

/*	Please see the license information at the end of this file. */

import java.util.*;
import java.util.regex.*;

import edu.northwestern.at.utils.corpuslinguistics.adornedword.*;
import edu.northwestern.at.utils.corpuslinguistics.postagger.*;
import edu.northwestern.at.utils.corpuslinguistics.postagger.unigram.*;
import edu.northwestern.at.utils.corpuslinguistics.tokenizer.*;

/**	Regular Expression Part of Speech tagger.
 *
 *	<p>
 *	The regular expression part of speech tagger uses a
 *	regular expressions to assign a part of speech tag to a spelling.
 *	</p>
 */

public class RegexpTagger extends UnigramTagger
	implements PartOfSpeechTagger, CanTagOneWord
{
	/**	Parts of speech for each lexical rule.
	 */

	protected Pattern[] regexpPatterns;
	protected Matcher[] regexpMatchers;
	protected String[] regexpTags;

	/**	Create a suffix tagger.
	 */

	public RegexpTagger()
	{
	}

	/**	See if tagger uses lexical rules.
	 *
	 *	@return		True since this tagger uses regular expression based
	 *				lexical rules.
	 */

	public boolean usesLexicalRules()
	{
		return true;
	}

	/**	Set lexical rules for tagging.
	 *
	 *	@param	lexicalRules	String array of lexical rules.
	 *
	 *	@throws	InvalidRuleException if a rule is bad.
	 *
	 *	<p>
	 *	For the regular expression tagger, each rule takes the form:
	 *	</p>
	 *
	 *	<blockquote>
	 *	<p>
	 *	<code>
	 *	regular-expression \t part-of-speech-tag
	 *	</code>
	 *	</p>
	 *	</blockquote>
	 *
	 *	<p>
	 *	where "regular expression" is the regular expression
	 *	and "part-of-speech-tag" is the part of speech tag to
	 *	assign to a spelling matched by the regular expression.
	 *	An ascii tab character (\t) separates the pattern from
	 *	the tag.
	 *	</p>
	 */

	public void setLexicalRules( String[] lexicalRules )
		throws InvalidRuleException
	{
		this.regexpPatterns	= new Pattern[ lexicalRules.length ];
		this.regexpMatchers	= new Matcher[ lexicalRules.length ];
		this.regexpTags		= new String[ lexicalRules.length ];

		for ( int i = 0 ; i < lexicalRules.length ; i++ )
		{
			String[] tokens				= lexicalRules[ i ].split( "\t" );
			this.regexpPatterns[ i ]	= Pattern.compile( tokens[ 0 ] );
			this.regexpMatchers[ i ]	=
				this.regexpPatterns[ i ].matcher( "" );
			this.regexpTags[ i ]		= tokens[ 1 ];
		}
	}

	/**	Tag a single word.
	 *
	 *	@param	word	The word.
	 *
	 *	@return			The part of speech for the word.
	 *
	 *	<p>
	 *	Applies each of the regular expressions stored in the lexical
	 *	rules lexicon and returns the tag of associated with the first
	 *	matching regular expression.
	 *	</p>
	 */

	public String tagWord( String word )
	{
		String result	= "";
								//	Try each regular expression in turn.

		for ( int i = 0 ; i < regexpMatchers.length ; i++ )
		{
			regexpMatchers[ i ].reset( word );

			if ( regexpMatchers[ i ].find() )
			{
				result	= regexpTags[ i ];
				break;
			}
		}

		return result;
	}

	/**	Return tagger description.
	 *
	 *	@return		Tagger description.
	 */

	public String toString()
	{
		return "Regular expression tagger";
	}
}

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   Northwestern University
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