AbstractLexicalSmoother.java

package edu.northwestern.at.utils.corpuslinguistics.postagger.smoothing.lexical;

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

import java.util.*;

import edu.northwestern.at.utils.*;
import edu.northwestern.at.utils.logger.*;
import edu.northwestern.at.utils.corpuslinguistics.lexicon.*;
import edu.northwestern.at.utils.corpuslinguistics.postagger.*;
import edu.northwestern.at.utils.math.*;

/**	Abstract lexical smoother.
 *
 *	<p>
 *	An abstract lexical smoother which provides implementations of
 *	common service methods such as setting the lexicon and the
 *	transition proability matrix.  Extend this class and override
 *	the abstract method "lexicalProbability" to produce a new
 *	lexical smoother.
 *	</p>
 */

abstract public class AbstractLexicalSmoother
	extends IsCloseableObject
	implements LexicalSmoother, UsesLogger
{
	/**	The part of speech tagger for which this smoother provides
	 *	amoother contextual probabilities.
	 */

	protected PartOfSpeechTagger partOfSpeechTagger;

	/**	Cached lexical probabilities for words.
	 */

	protected Map2D<String, String, Probability> cachedLexicalProbabilities;

	/**	Logger used for output. */

	protected Logger logger;

	/**	Create an abstract lexical smoother.
	 */

	public AbstractLexicalSmoother()
	{
								//	Create cache for lexical
								//	probabilities.

		cachedLexicalProbabilities	=
			Map2DFactory.createNewMap2D( 3000 );

								//	Create dummy logger.

		logger						= new DummyLogger();
	}

	/**	Get the logger.
	 *
	 *	@return		The logger.
	 */

	public Logger getLogger()
	{
		return logger;
	}

	/**	Set the logger.
	 *
	 *	@param	logger		The logger.
	 */

	public void setLogger( Logger logger )
	{
		this.logger	= logger;
	}

	/**	Set the part of speech tagger for this smoother.
	 *
	 *	@param	partOfSpeechTagger	Part of speech tagger for which
	 *								this smoother provides probabilities.
	 */

	public void setPartOfSpeechTagger
	(
		PartOfSpeechTagger partOfSpeechTagger
	)
	{
		this.partOfSpeechTagger	= partOfSpeechTagger;
	}

	/**	Get the number of cached lexical probabilities.
	 *
	 *	@return		The number of cached lexical probabilities.
	 */

	public int cachedProbabilitiesCount()
	{
		int result	= 0;

		if ( cachedLexicalProbabilities != null )
		{
			result	= cachedLexicalProbabilities.size();
		}

		return result;
	}

	/**	Clear cached probabilities..
	 */

	public void clearCachedProbabilities()
	{
		cachedLexicalProbabilities.clear();
	}

	/**	Get lexically smoothed probability of a word given a tag.
	 *
	 *	@param	word	The word.
	 *	@param	tag		The part of speech tag.
	 *
	 *	@return			Lexically smoothed probability of word given tag,
	 *					e.g., p( word | tag ).
	 *
 	 *	<p>
 	 *	To avoid redoing potentially expensive probability calculations,
 	 *	you can use the "cachedLexicalProbabilities" HashMap2D to store
 	 *	probabilities once they are calculated.  Your lexicalProbability
 	 *	method should look to see if the cache contains the needed
 	 *	lexical probability.  If so, just retrieve it without recomputing it.
 	 *	If the cache does not contain the probability, compute it, and
	 *	store it in the cache for future use.
 	 *	</p>
 	 *
 	 *	<p>
 	 *	Here is what a lexicalProbability method should look like, using
 	 *	the cache.
	 *	<p>
	 *
	 *	<p>
	 *	<pre>
	 *	protected Probability lexicalProbability( String word , String tag )
	 *	{
	 *								//	See if the lexical probability
	 *								//	p( word | tag ) is in the cache.
	 *
	 *		Probability result	=
	 *			(Probability)cachedLexicalProbabilities.get( word , tag );
     *
	 *								//	If the probability isn't in the
	 *								//	cache, compute it.
	 *
	 *		if ( result == null )
	 *		{
	 *			double prob		= <em>compute smoothed probability value</em>
	 *
	 *								//	Store computed probability in
	 *								//	the cache.
	 *
	 *			result	= new Probability( prob );
	 *
	 *			cachedLexicalProbabilities.put( word , tag , result );
	 *		}
	 *
	 *		return result;
	 *	}
	 *	</pre>
	 *	</p>
	 */

	 public abstract Probability lexicalProbability
	 (
	 	String word ,
	 	String tag
	 );
}

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