edu.northwestern.at.morphadorner.corpuslinguistics.postagger.smoothing.contextual

Class DeletedInterpolationContextualSmoother

java.lang.Object

edu.northwestern.at.utils.IsCloseableObject

edu.northwestern.at.morphadorner.corpuslinguistics.postagger.smoothing.contextual.AbstractContextualSmoother

edu.northwestern.at.morphadorner.corpuslinguistics.postagger.smoothing.contextual.DeletedInterpolationContextualSmoother

All Implemented Interfaces:

ContextualSmoother, UsesLogger

public class DeletedInterpolationContextualSmoother
extends AbstractContextualSmoother
implements ContextualSmoother

DeletedInterpolation contextual smoother.

A contextual smoother which a weighted combination of unigram and bigram probabilities (for a bigram tagger) or unigram bigram, and trigram probabilities (for a trigram tagger).

Field Summary

Fields

Modifier and Type	Field and Description
protected double[]	bigramWeights Bigram weights for lexical smoothing.
protected double[]	trigramWeights Trigram weights for lexical smoothing.

Fields inherited from class edu.northwestern.at.morphadorner.corpuslinguistics.postagger.smoothing.contextual.AbstractContextualSmoother

cachedContextualProbabilities, logger, partOfSpeechTagger

Constructor Summary

Constructors

Constructor and Description
DeletedInterpolationContextualSmoother() Create a deleted interpolation contextual smoother.

Method Summary

Methods

Modifier and Type	Method and Description
Probability	contextualProbability(java.lang.String tag, java.lang.String previousTag) Compute contextual probability of a tag given the previous tag.
Probability	contextualProbability(java.lang.String tag, java.lang.String previousTag, java.lang.String previousPreviousTag) Compute contextual probability of a tag given the previous tags.
java.lang.String	toString() Description of this smoother for display.

Methods inherited from class edu.northwestern.at.morphadorner.corpuslinguistics.postagger.smoothing.contextual.AbstractContextualSmoother

cachedProbabilitiesCount, clearCachedProbabilities, getLogger, setLogger, setPartOfSpeechTagger

Methods inherited from class edu.northwestern.at.utils.IsCloseableObject

close

Methods inherited from class java.lang.Object

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

Methods inherited from interface edu.northwestern.at.morphadorner.corpuslinguistics.postagger.smoothing.contextual.ContextualSmoother

cachedProbabilitiesCount, clearCachedProbabilities, setPartOfSpeechTagger

Field Detail

bigramWeights

protected double[] bigramWeights

Bigram weights for lexical smoothing.

trigramWeights

protected double[] trigramWeights

Trigram weights for lexical smoothing.

Constructor Detail

DeletedInterpolationContextualSmoother

public DeletedInterpolationContextualSmoother()

Create a deleted interpolation contextual smoother.

Method Detail

contextualProbability

public Probability contextualProbability(java.lang.String tag,
                                java.lang.String previousTag)

Compute contextual probability of a tag given the previous tag.

Specified by:

contextualProbability in interface ContextualSmoother

Specified by:

contextualProbability in class AbstractContextualSmoother

Parameters:

tag - The current tag.

previousTag - The previous tag.

Returns:

The probability of the current tag given the previous tag, e.g, p( tag | previousTag ).

We compute the contextual probability p( tag | previousTag ) using weights determined by deleted interpolation. The smoothed contextual probability is given by:

p*( tag | previousTag ) = l1 * p( tag ) + l2 * p( previousTag , tag )

where l1 and l2 are the unigram and bigram weights respectively.

contextualProbability

public Probability contextualProbability(java.lang.String tag,
                                java.lang.String previousTag,
                                java.lang.String previousPreviousTag)

Compute contextual probability of a tag given the previous tags.

Specified by:

contextualProbability in interface ContextualSmoother

Parameters:

tag - The current tag.

previousTag - The previous tag.

previousPreviousTag - The previous tag of the previous tag.

Returns:

The probability of the current tag given the previous two tags, e.g, p( tag | prevTag , prevPrevTag ).

We compute the contextual probability p( tag | previousPreviousTag , previousTag ) using weights determined by deleted interpolation. The smoothed contextual probability is given by:

p*( tag | previousPreviousTag , previousTag ) = l1 * p( tag ) + l2 * p( previousTag , tag ) + l3 * o( previousPreviousTag , previousTag , tag )

where l1, l2, and l3 are the unigram, bigram, and trigram weights respectively.

toString

public java.lang.String toString()

Description of this smoother for display.

Overrides:

toString in class java.lang.Object

Returns:

Description of this smoother.