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java.lang.Objectorg.apache.lucene.search.similarities.Similarity
org.apache.lucene.search.similarities.SimilarityBase
org.apache.lucene.search.similarities.DFRSimilarity
public 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.
Note that qtf, the multiplicity of term-occurrence in the query, is not handled by this implementation.
BasicModel
,
AfterEffect
,
Normalization
Nested Class Summary |
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Nested classes/interfaces inherited from class org.apache.lucene.search.similarities.Similarity |
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Similarity.ExactSimScorer, Similarity.SimWeight, Similarity.SloppySimScorer |
Field Summary | |
---|---|
protected AfterEffect |
afterEffect
The first normalization of the information content. |
protected BasicModel |
basicModel
The basic model for information content. |
protected Normalization |
normalization
The term frequency normalization. |
Fields inherited from class org.apache.lucene.search.similarities.SimilarityBase |
---|
discountOverlaps |
Constructor Summary | |
---|---|
DFRSimilarity(BasicModel basicModel,
AfterEffect afterEffect,
Normalization normalization)
|
Method Summary | |
---|---|
protected void |
explain(Explanation expl,
BasicStats stats,
int doc,
float freq,
float docLen)
Subclasses should implement this method to explain the score. |
AfterEffect |
getAfterEffect()
|
BasicModel |
getBasicModel()
|
Normalization |
getNormalization()
|
protected float |
score(BasicStats stats,
float freq,
float docLen)
Scores the document doc . |
String |
toString()
Subclasses must override this method to return the name of the Similarity and preferably the values of parameters (if any) as well. |
Methods inherited from class org.apache.lucene.search.similarities.SimilarityBase |
---|
computeNorm, computeWeight, decodeNormValue, encodeNormValue, exactSimScorer, explain, fillBasicStats, getDiscountOverlaps, log2, newStats, setDiscountOverlaps, sloppySimScorer |
Methods inherited from class org.apache.lucene.search.similarities.Similarity |
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coord, queryNorm |
Methods inherited from class java.lang.Object |
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clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait |
Field Detail |
---|
protected final BasicModel basicModel
protected final AfterEffect afterEffect
protected final Normalization normalization
Constructor Detail |
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public DFRSimilarity(BasicModel basicModel, AfterEffect afterEffect, Normalization normalization)
Method Detail |
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protected float score(BasicStats stats, float freq, float docLen)
SimilarityBase
doc
.
Subclasses must apply their scoring formula in this class.
score
in class SimilarityBase
stats
- the corpus level statistics.freq
- the term frequency.docLen
- the document length.
protected void explain(Explanation expl, BasicStats stats, int doc, float freq, float docLen)
SimilarityBase
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.
explain
in class SimilarityBase
expl
- the explanation to extend with details.stats
- the corpus level statistics.doc
- the document id.freq
- the term frequency.docLen
- the document length.public String toString()
SimilarityBase
toString
in class SimilarityBase
public BasicModel getBasicModel()
public AfterEffect getAfterEffect()
public Normalization getNormalization()
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