Class IBSimilarity

Provides a framework for the family of information-based models, as described in StÉphane Clinchant and Eric Gaussier. 2010. Information-based models for ad hoc IR. In Proceeding of the 33rd international ACM SIGIR conference on Research and development in information retrieval (SIGIR '10). ACM, New York, NY, USA, 234-241.

The retrieval function is of the form RSV(q, d) = ∑ -xqw log Prob(Xw >= tdw | λw), where

  • xqw is the query boost;
  • Xw is a random variable that counts the occurrences of word w;
  • tdw is the normalized term frequency;
  • λw is a parameter.

The framework described in the paper has many similarities to the DFR framework (see DFRSimilarity). It is possible that the two Similarities will be merged at one point.

To construct an IBSimilarity, you must specify the implementations for all three components of the Information-Based model.

ComponentImplementations
Distribution: Probabilistic distribution used to model term occurrence
Lambda: λw parameter of the probability distribution
  • LambdaDF: Nw/N or average number of documents where w occurs
  • LambdaTTF: Fw/N or average number of occurrences of w in the collection
Normalization: Term frequency normalizationAny supported DFR normalization (listed in DFRSimilarity)

Note

This API is experimental and might change in incompatible ways in the next release.

Inheritance
System.Object
Similarity
SimilarityBase
IBSimilarity
Inherited Members
System.Object.Equals(System.Object)
System.Object.Equals(System.Object, System.Object)
System.Object.GetHashCode()
System.Object.GetType()
System.Object.MemberwiseClone()
System.Object.ReferenceEquals(System.Object, System.Object)
Namespace: Lucene.Net.Search.Similarities
Assembly: Lucene.Net.dll
Syntax
public class IBSimilarity : SimilarityBase

Constructors

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IBSimilarity(Distribution, Lambda, Normalization)

Creates IBSimilarity from the three components.

Note that null values are not allowed: if you want no normalization, instead pass Normalization.NoNormalization.

Declaration
public IBSimilarity(Distribution distribution, Lambda lambda, Normalization normalization)
Parameters
Type Name Description
Distribution distribution

probabilistic distribution modeling term occurrence

Lambda lambda

distribution's λw parameter

Normalization normalization

term frequency normalization

Fields

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m_distribution

The probabilistic distribution used to model term occurrence.

Declaration
protected readonly Distribution m_distribution
Field Value
Type Description
Distribution
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m_lambda

The lambda (λw) parameter.

Declaration
protected readonly Lambda m_lambda
Field Value
Type Description
Lambda
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m_normalization

The term frequency normalization.

Declaration
protected readonly Normalization m_normalization
Field Value
Type Description
Normalization

Properties

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Distribution

Returns the distribution

Declaration
public virtual Distribution Distribution { get; }
Property Value
Type Description
Distribution
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Lambda

Returns the distribution's lambda parameter

Declaration
public virtual Lambda Lambda { get; }
Property Value
Type Description
Lambda
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Normalization

Returns the term frequency normalization

Declaration
public virtual Normalization Normalization { get; }
Property Value
Type Description
Normalization

Methods

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Explain(Explanation, BasicStats, Int32, Single, Single)

Declaration
protected override void Explain(Explanation expl, BasicStats stats, int doc, float freq, float docLen)
Parameters
Type Name Description
Explanation expl
BasicStats stats
System.Int32 doc
System.Single freq
System.Single docLen
Overrides
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Score(BasicStats, Single, Single)

Declaration
public override float Score(BasicStats stats, float freq, float docLen)
Parameters
Type Name Description
BasicStats stats
System.Single freq
System.Single docLen
Returns
Type Description
System.Single
Overrides
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ToString()

The name of IB methods follow the pattern IB <distribution> <lambda><normalization>. The name of the distribution is the same as in the original paper; for the names of lambda parameters, refer to the doc of the Lambda classes.

Declaration
public override string ToString()
Returns
Type Description
System.String
Overrides

See Also