Package org.terrier.matching.models
Class BM25
- java.lang.Object
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- org.terrier.matching.models.WeightingModel
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- org.terrier.matching.models.BM25
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- All Implemented Interfaces:
java.io.Serializable
,java.lang.Cloneable
,Model
public class BM25 extends WeightingModel
This class implements the Okapi BM25 weighting model. This has a number of parameters that can be set using controls in the (Search)Request object.- bm25.k_1 = 1.2d
- bm25.k_3 = 8d
- bm25.b = 0.75d
- Author:
- Gianni Amati, Ben He, Vassilis Plachouras
- See Also:
- Serialized Form
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Field Summary
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Fields inherited from class org.terrier.matching.models.WeightingModel
averageDocumentLength, cs, documentFrequency, es, i, keyFrequency, numberOfDocuments, numberOfPointers, numberOfPostings, numberOfTokens, numberOfUniqueTerms, rq, termFrequency
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Constructor Summary
Constructors Constructor Description BM25()
A default constructor.
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Method Summary
All Methods Instance Methods Concrete Methods Deprecated Methods Modifier and Type Method Description java.lang.String
getInfo()
Returns the name of the model.double
getParameter()
Deprecated.void
prepare()
preparedouble
score(double tf, double docLength)
Uses BM25 to compute a weight for a term in a document.void
setParameter(double _b)
Deprecated.-
Methods inherited from class org.terrier.matching.models.WeightingModel
clone, getOverflowed, score, setCollectionStatistics, setEntryStatistics, setKeyFrequency, setRequest
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Method Detail
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getInfo
public final java.lang.String getInfo()
Returns the name of the model.- Specified by:
getInfo
in interfaceModel
- Specified by:
getInfo
in classWeightingModel
- Returns:
- the name of the model
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score
public double score(double tf, double docLength)
Uses BM25 to compute a weight for a term in a document.- Specified by:
score
in classWeightingModel
- Parameters:
tf
- The term frequency in the documentdocLength
- the document's length- Returns:
- the score assigned to a document with the given tf and docLength, and other preset parameters
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prepare
public void prepare()
Description copied from class:WeightingModel
prepare- Overrides:
prepare
in classWeightingModel
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setParameter
@Deprecated public void setParameter(double _b)
Deprecated.Sets the b parameter to BM25 ranking formula- Specified by:
setParameter
in interfaceModel
- Overrides:
setParameter
in classWeightingModel
- Parameters:
_b
- the b parameter value to use.
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getParameter
@Deprecated public double getParameter()
Deprecated.Returns the b parameter to the BM25 ranking formula as set by setParameter()- Specified by:
getParameter
in interfaceModel
- Overrides:
getParameter
in classWeightingModel
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