Class DFRSimilarity

Implements the divergence from randomness (DFR) framework introduced in Gianni Amati and Cornelis Joost Van Rijsbergen. 2002. Probabilistic models of information retrieval based on measuring the divergence from randomness. ACM Trans. Inf. Syst. 20, 4 (October 2002), 357-389.

The DFR scoring formula is composed of three separate components: the basic model, the aftereffect and an additional normalization component, represented by the classes BasicModel, AfterEffect and Normalization, respectively. The names of these classes were chosen to match the names of their counterparts in the Terrier IR engine.

To construct a DFRSimilarity, you must specify the implementations for all three components of DFR:

ComponentImplementations
BasicModel: Basic model of information content:
AfterEffect: First normalization of information gain:
Normalization: Second (length) normalization:

Note that qtf, the multiplicity of term-occurrence in the query, is not handled by this implementation.

This is a Lucene.NET EXPERIMENTAL API, use at your own risk
Inheritance
System.Object
Similarity
SimilarityBase
DFRSimilarity
Inherited Members
Namespace: Lucene.Net.Search.Similarities
Assembly: Lucene.Net.dll
Syntax
public class DFRSimilarity : SimilarityBase

Constructors

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DFRSimilarity(BasicModel, AfterEffect, Normalization)

Creates DFRSimilarity from the three components.

Note that null values are not allowed: if you want no normalization or after-effect, instead pass Normalization.NoNormalization or AfterEffect.NoAfterEffect respectively.

Declaration
public DFRSimilarity(BasicModel basicModel, AfterEffect afterEffect, Normalization normalization)
Parameters
Type Name Description
BasicModel basicModel

Basic model of information content

AfterEffect afterEffect

First normalization of information gain

Normalization normalization

Second (length) normalization

Fields

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m_afterEffect

The first normalization of the information content.

Declaration
protected readonly AfterEffect m_afterEffect
Field Value
Type Description
AfterEffect
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m_basicModel

The basic model for information content.

Declaration
protected readonly BasicModel m_basicModel
Field Value
Type Description
BasicModel
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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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AfterEffect

Returns the first normalization

Declaration
public virtual AfterEffect AfterEffect { get; }
Property Value
Type Description
AfterEffect
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BasicModel

Returns the basic model of information content

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

Returns the second 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()

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

See Also