ProperNounRetagger.java

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

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

import java.util.*;

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

/**	A proper noun retagger.
 *
 *	<p>
 *	This retagger applies a short list of rules to improve tagging
 *	of proper nouns.
 *	</p>
 */

public class ProperNounRetagger
	extends UnigramTagger
	implements PartOfSpeechRetagger
{
	/**	Part of speech tags. */

	protected static PartOfSpeechTags posTags;

	/**	Create proper noun retagger.
	 */

	public ProperNounRetagger()
	{
		super();
	}

	/**	Retag a sentence.
	 *
	 *	@param	sentence	The sentence as an
	 *						{@link edu.northwestern.at.utils.corpuslinguistics.adornedword.AdornedWord} .
	 *
	 *	@return				The sentence with words retagged.
	 */

	public<T extends AdornedWord> List<T> retagSentence
	(
		List<T> sentence
	)
	{
								//	Get noun part of speech tags
								//	if we don't already have them.

		if ( posTags == null )
		{
			posTags	= getLexicon().getPartOfSpeechTags();
		}
								//	Examine all words in sentence to
								//	see if we should change nouns
								//	to proper nouns.  We do this
								//	if a noun has an initial capital letter.
								//	Note that we skip the first word of
								//	the sentence since the capitalization
								//	check is uninformative in this case.
								//	We also change proper nouns to
								//	common nouns when the word is not
								//	capitalized.

		for ( int i = 1 ; i < sentence.size() ; i++ )
		{
								//	Get next word in sentence.

			AdornedWord adornedWord	= sentence.get( i );

                                //	Get spelling.

			String spelling			= adornedWord.getSpelling();

								//	Is spelling capitalized?

			boolean isCapitalized	=
				Character.isUpperCase( spelling.charAt( 0 ) );

								//	See if word is a proper noun.
								//	Change it to a common noun if it
								//	is not capitalized.

			if ( !isCapitalized  )
			{
				String partsOfSpeech	= adornedWord.getPartsOfSpeech();

				if ( posTags.isProperNounTag( partsOfSpeech ) )
				{
					adornedWord.setPartsOfSpeech
					(
						posTags.getCorrespondingCommonNounTag(
							partsOfSpeech )
					);
				}
				else if ( posTags.isProperAdjectiveTag( partsOfSpeech ) )
				{
					adornedWord.setPartsOfSpeech( posTags.getAdjectiveTag() );
				}
			}
		}
								//	Return updated sentence.
		return sentence;
	}

	/**	Can retagger add or delete words in the original sentence?
	 *
	 *	@return		true if retagger can add or delete words.
	 */

	public boolean canAddOrDeleteWords()
	{
		return false;
	}

	/**	Return retagger description.
	 *
	 *	@return		Retagger description.
	 */

	public String toString()
	{
		return "Proper noun retagger";
	}
}

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