org.apache.lucene.search.similarities

Class Axiomatic

java.lang.Object

org.apache.lucene.search.similarities.Similarity

org.apache.lucene.search.similarities.SimilarityBase

org.apache.lucene.search.similarities.Axiomatic

Direct Known Subclasses:

AxiomaticF1EXP, AxiomaticF1LOG, AxiomaticF2EXP, AxiomaticF2LOG, AxiomaticF3EXP, AxiomaticF3LOG

public abstract class Axiomatic
extends SimilarityBase

Axiomatic approaches for IR. From Hui Fang and Chengxiang Zhai 2005. An Exploration of Axiomatic Approaches to Information Retrieval. In Proceedings of the 28th annual international ACM SIGIR conference on Research and development in information retrieval (SIGIR '05). ACM, New York, NY, USA, 480-487.

There are a family of models. All of them are based on BM25, Pivoted Document Length Normalization and Language model with Dirichlet prior. Some components (e.g. Term Frequency, Inverted Document Frequency) in the original models are modified so that they follow some axiomatic constraints.

WARNING: This API is experimental and might change in incompatible ways in the next release.

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.lucene.search.similarities.Similarity

Similarity.SimScorer, Similarity.SimWeight

Field Summary

Fields

Modifier and Type	Field and Description
protected float	k hyperparam for the primitive weighthing function
protected int	queryLen the query length
protected float	s hyperparam for the growth function

Fields inherited from class org.apache.lucene.search.similarities.SimilarityBase

discountOverlaps

Constructor Summary

Constructors

Constructor and Description
Axiomatic() Default constructor
Axiomatic(float s) Constructor setting only s, letting k and queryLen to default
Axiomatic(float s, int queryLen) Constructor setting s and queryLen, letting k to default
Axiomatic(float s, int queryLen, float k) Constructor setting all Axiomatic hyperparameters

Method Summary

Modifier and Type	Method and Description
protected void	explain(List<Explanation> subs, BasicStats stats, int doc, float freq, float docLen) Subclasses should implement this method to explain the score.
protected abstract float	gamma(BasicStats stats, float freq, float docLen) compute the gamma component (only for F3EXp and F3LOG)
protected abstract float	idf(BasicStats stats, float freq, float docLen) compute the inverted document frequency component
protected abstract float	ln(BasicStats stats, float freq, float docLen) compute the document length component
float	score(BasicStats stats, float freq, float docLen) Scores the document doc.
protected abstract float	tf(BasicStats stats, float freq, float docLen) compute the term frequency component
protected abstract float	tfln(BasicStats stats, float freq, float docLen) compute the mixed term frequency and document length component
abstract String	toString() Name of the axiomatic method.

Methods inherited from class org.apache.lucene.search.similarities.SimilarityBase

computeNorm, computeWeight, explain, fillBasicStats, getDiscountOverlaps, log2, newStats, setDiscountOverlaps, simScorer

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

s

protected final float s

hyperparam for the growth function

k

protected final float k

hyperparam for the primitive weighthing function

queryLen

protected final int queryLen

the query length

Constructor Detail

Axiomatic

public Axiomatic(float s,
                 int queryLen,
                 float k)

Constructor setting all Axiomatic hyperparameters

Parameters:

s - hyperparam for the growth function

queryLen - the query length

k - hyperparam for the primitive weighting function

Axiomatic

public Axiomatic(float s)

Constructor setting only s, letting k and queryLen to default

Parameters:

s - hyperparam for the growth function

Axiomatic

public Axiomatic(float s,
                 int queryLen)

Constructor setting s and queryLen, letting k to default

Parameters:

s - hyperparam for the growth function

queryLen - the query length

Axiomatic

public Axiomatic()

Default constructor

Method Detail

score

public float score(BasicStats stats,
                   float freq,
                   float docLen)

Description copied from class: SimilarityBase

Scores the document doc.

Subclasses must apply their scoring formula in this class.

Specified by:

score in class SimilarityBase

Parameters:

stats - the corpus level statistics.

freq - the term frequency.

docLen - the document length.

Returns:

the score.

explain

protected void explain(List<Explanation> subs,
                       BasicStats stats,
                       int doc,
                       float freq,
                       float docLen)

Description copied from class: SimilarityBase

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.

Overrides:

explain in class SimilarityBase

Parameters:

subs - the list of details of the explanation to extend

stats - the corpus level statistics.

doc - the document id.

freq - the term frequency.

docLen - the document length.

toString

public abstract String toString()

Name of the axiomatic method.

Specified by:

toString in class SimilarityBase

tf

protected abstract float tf(BasicStats stats,
                            float freq,
                            float docLen)

compute the term frequency component

ln

protected abstract float ln(BasicStats stats,
                            float freq,
                            float docLen)

compute the document length component

tfln

protected abstract float tfln(BasicStats stats,
                              float freq,
                              float docLen)

compute the mixed term frequency and document length component

idf

protected abstract float idf(BasicStats stats,
                             float freq,
                             float docLen)

compute the inverted document frequency component

gamma

protected abstract float gamma(BasicStats stats,
                               float freq,
                               float docLen)

compute the gamma component (only for F3EXp and F3LOG)