Class SimilarityBase

A subclass of Similarity that provides a simplified API for its descendants. Subclasses are only required to implement the Score(BasicStats, Single, Single) and ToString() methods. Implementing Explain(Explanation, BasicStats, Int32, Single, Single) is optional, inasmuch as SimilarityBase already provides a basic explanation of the score and the term frequency. However, implementers of a subclass are encouraged to include as much detail about the scoring method as possible.

Note: multi-word queries such as phrase queries are scored in a different way than Lucene's default ranking algorithm: whereas it "fakes" an IDF value for the phrase as a whole (since it does not know it), this class instead scores phrases as a summation of the individual term scores.

This is a Lucene.NET EXPERIMENTAL API, use at your own risk

Inheritance

System.Object

Similarity

SimilarityBase

DFRSimilarity

IBSimilarity

LMSimilarity

Inherited Members

Similarity.Coord(Int32, Int32)

Similarity.QueryNorm(Single)

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 abstract class SimilarityBase : Similarity

Constructors

SimilarityBase()

Sole constructor. (For invocation by subclass constructors, typically implicit.)

Declaration

public SimilarityBase()

Properties

DiscountOverlaps

Determines whether overlap tokens (Tokens with 0 position increment) are ignored when computing norm. By default this is true, meaning overlap tokens do not count when computing norms.

This is a Lucene.NET EXPERIMENTAL API, use at your own risk

Declaration

public virtual bool DiscountOverlaps { get; set; }

Property Value

Type	Description
System.Boolean

See Also

ComputeNorm(FieldInvertState)

Methods

ComputeNorm(FieldInvertState)

Encodes the document length in the same way as TFIDFSimilarity.

Declaration

public override long ComputeNorm(FieldInvertState state)

Parameters

Type	Name	Description
FieldInvertState	state

Returns

Type	Description
System.Int64

Overrides

Similarity.ComputeNorm(FieldInvertState)

ComputeWeight(Single, CollectionStatistics, TermStatistics[])

Declaration

public override sealed Similarity.SimWeight ComputeWeight(float queryBoost, CollectionStatistics collectionStats, params TermStatistics[] termStats)

Parameters

Type	Name	Description
System.Single	queryBoost
CollectionStatistics	collectionStats
TermStatistics[]	termStats

Returns

Type	Description
Similarity.SimWeight

Overrides

Similarity.ComputeWeight(Single, CollectionStatistics, TermStatistics[])

DecodeNormValue(Byte)

Decodes a normalization factor (document length) stored in an index.

Declaration

protected virtual float DecodeNormValue(byte norm)

Parameters

Type	Name	Description
System.Byte	norm

Returns

Type	Description
System.Single

EncodeNormValue(Single, Single)

Encodes the length to a byte via SmallSingle.

Declaration

protected virtual byte EncodeNormValue(float boost, float length)

Parameters

Type	Name	Description
System.Single	boost
System.Single	length

Returns

Type	Description
System.Byte

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

Subclasses should implement this method to explain the score. expl already contains the score, the name of the class and the doc id, as well as the term frequency and its explanation; subclasses can add additional clauses to explain details of their scoring formulae.

The default implementation does nothing.

Declaration

protected virtual void Explain(Explanation expl, BasicStats stats, int doc, float freq, float docLen)

Parameters

Type	Name	Description
Explanation	expl	the explanation to extend with details.
BasicStats	stats	the corpus level statistics.
System.Int32	doc	the document id.
System.Single	freq	the term frequency.
System.Single	docLen	the document length.

Explain(BasicStats, Int32, Explanation, Single)

Explains the score. The implementation here provides a basic explanation in the format Score(name-of-similarity, doc=doc-id, freq=term-frequency), computed from:, and attaches the score (computed via the Score(BasicStats, Single, Single) method) and the explanation for the term frequency. Subclasses content with this format may add additional details in Explain(Explanation, BasicStats, Int32, Single, Single).

Declaration

public virtual Explanation Explain(BasicStats stats, int doc, Explanation freq, float docLen)

Parameters

Type	Name	Description
BasicStats	stats	the corpus level statistics.
System.Int32	doc	the document id.
Explanation	freq	the term frequency and its explanation.
System.Single	docLen	the document length.

Returns

Type	Description
Explanation	the explanation.

FillBasicStats(BasicStats, CollectionStatistics, TermStatistics)

Fills all member fields defined in BasicStats in stats. Subclasses can override this method to fill additional stats.

Declaration

protected virtual void FillBasicStats(BasicStats stats, CollectionStatistics collectionStats, TermStatistics termStats)

Parameters

Type	Name	Description
BasicStats	stats
CollectionStatistics	collectionStats
TermStatistics	termStats

GetSimScorer(Similarity.SimWeight, AtomicReaderContext)

Declaration

public override Similarity.SimScorer GetSimScorer(Similarity.SimWeight stats, AtomicReaderContext context)

Parameters

Type	Name	Description
Similarity.SimWeight	stats
AtomicReaderContext	context

Returns

Type	Description
Similarity.SimScorer

Overrides

Similarity.GetSimScorer(Similarity.SimWeight, AtomicReaderContext)

Log2(Double)

Returns the base two logarithm of x.

Declaration

public static double Log2(double x)

Parameters

Type	Name	Description
System.Double	x

Returns

Type	Description
System.Double

NewStats(String, Single)

Factory method to return a custom stats object

Declaration

protected virtual BasicStats NewStats(string field, float queryBoost)

Parameters

Type	Name	Description
System.String	field
System.Single	queryBoost

Returns

Type	Description
BasicStats

Score(BasicStats, Single, Single)

Scores the document doc.

Subclasses must apply their scoring formula in this class.

Declaration

public abstract float Score(BasicStats stats, float freq, float docLen)

Parameters

Type	Name	Description
BasicStats	stats	the corpus level statistics.
System.Single	freq	the term frequency.
System.Single	docLen	the document length.

Returns

Type	Description
System.Single	the score.

ToString()

Subclasses must override this method to return the name of the Similarity and preferably the values of parameters (if any) as well.

Declaration

public abstract override string ToString()

Returns

Type	Description
System.String

Overrides

System.Object.ToString()