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    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
    • DistributionLL: Log-logistic
    • DistributionLL: Smoothed power-law
    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)

    This is a Lucene.NET EXPERIMENTAL API, use at your own risk
    Inheritance
    System.Object
    Similarity
    SimilarityBase
    IBSimilarity
    Inherited Members
    SimilarityBase.DiscountOverlaps
    SimilarityBase.ComputeWeight(Single, CollectionStatistics, TermStatistics[])
    SimilarityBase.NewStats(String, Single)
    SimilarityBase.FillBasicStats(BasicStats, CollectionStatistics, TermStatistics)
    SimilarityBase.Explain(BasicStats, Int32, Explanation, Single)
    SimilarityBase.GetSimScorer(Similarity.SimWeight, AtomicReaderContext)
    SimilarityBase.ComputeNorm(FieldInvertState)
    SimilarityBase.DecodeNormValue(Byte)
    SimilarityBase.EncodeNormValue(Single, Single)
    SimilarityBase.Log2(Double)
    Similarity.Coord(Int32, Int32)
    Similarity.QueryNorm(Single)
    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
    SimilarityBase.Explain(Explanation, BasicStats, Int32, Single, Single)
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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
    SimilarityBase.Score(BasicStats, Single, Single)
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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
    SimilarityBase.ToString()

    See Also

    DFRSimilarity
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