org.apache.lucene.search.similarities

Class LMSimilarity

java.lang.Object

org.apache.lucene.search.similarities.Similarity

org.apache.lucene.search.similarities.SimilarityBase

org.apache.lucene.search.similarities.LMSimilarity

Direct Known Subclasses:

LMDirichletSimilarity, LMJelinekMercerSimilarity

public abstract class LMSimilarity
extends SimilarityBase

Abstract superclass for language modeling Similarities. The following inner types are introduced:

• LMSimilarity.LMStats, which defines a new statistic, the probability that the collection language model generates the current term;
• LMSimilarity.CollectionModel, which is a strategy interface for object that compute the collection language model p(w|C);
• LMSimilarity.DefaultCollectionModel, an implementation of the former, that computes the term probability as the number of occurrences of the term in the collection, divided by the total number of tokens.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	LMSimilarity.CollectionModel A strategy for computing the collection language model.
static class	LMSimilarity.DefaultCollectionModel Models p(w|C) as the number of occurrences of the term in the collection, divided by the total number of tokens + 1.
static class	LMSimilarity.LMStats Stores the collection distribution of the current term.

Nested classes/interfaces inherited from class org.apache.lucene.search.similarities.Similarity

Similarity.SimScorer, Similarity.SimWeight

Constructor Summary

Constructors

Constructor and Description
LMSimilarity() Creates a new instance with the default collection language model.
LMSimilarity(LMSimilarity.CollectionModel collectionModel) Creates a new instance with the specified collection language model.

Method Summary

Modifier and Type	Method and Description
abstract String	getName() Returns the name of the LM method.
String	toString() Returns the name of the LM method.

Methods inherited from class org.apache.lucene.search.similarities.SimilarityBase

computeNorm, computeWeight, getDiscountOverlaps, log2, setDiscountOverlaps, simScorer

Methods inherited from class org.apache.lucene.search.similarities.Similarity

coord, queryNorm

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

LMSimilarity

public LMSimilarity(LMSimilarity.CollectionModel collectionModel)

Creates a new instance with the specified collection language model.

LMSimilarity

public LMSimilarity()

Creates a new instance with the default collection language model.

Method Detail

getName

public abstract String getName()

Returns the name of the LM method. The values of the parameters should be included as well.

Used in toString()

.

toString

public String toString()

Returns the name of the LM method. If a custom collection model strategy is used, its name is included as well.

Specified by:

toString in class SimilarityBase

See Also:

getName(), LMSimilarity.CollectionModel.getName(), LMSimilarity.DefaultCollectionModel