de.datexis.index.utils

Class ContextSimilarity

java.lang.Object

org.apache.lucene.search.similarities.Similarity

org.apache.lucene.search.similarities.TFIDFSimilarity

org.apache.lucene.search.similarities.ClassicSimilarity

de.datexis.index.utils.ContextSimilarity

public class ContextSimilarity
extends org.apache.lucene.search.similarities.ClassicSimilarity

Term similarity without normalization for Lucene.

Author:

sarnold

Nested Class Summary

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

org.apache.lucene.search.similarities.Similarity.SimScorer, org.apache.lucene.search.similarities.Similarity.SimWeight

Field Summary

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

discountOverlaps

Constructor Summary

Constructors

Constructor and Description
ContextSimilarity()

Method Summary

Modifier and Type	Method and Description
float	coord(int overlap, int maxOverlap) Computes a score factor based on the fraction of all query terms that a document contains.
float	lengthNorm(org.apache.lucene.index.FieldInvertState state) Compute an index-time normalization value for this field instance.
float	queryNorm(float sumOfSquaredWeights) Computes the normalization value for a query given the sum of the squared weights of each of the query terms.

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

decodeNormValue, encodeNormValue, getDiscountOverlaps, idf, scorePayload, setDiscountOverlaps, sloppyFreq, tf, toString

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

computeNorm, computeWeight, idfExplain, idfExplain, simScorer

Methods inherited from class java.lang.Object

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

Constructor Detail

ContextSimilarity

public ContextSimilarity()

Method Detail

lengthNorm

public float lengthNorm(org.apache.lucene.index.FieldInvertState state)

Compute an index-time normalization value for this field instance.

This value will be stored in a single byte lossy representation by ClassicSimilarity.encodeNormValue(float).

Overrides:

lengthNorm in class org.apache.lucene.search.similarities.ClassicSimilarity

Parameters:

state - statistics of the current field (such as length, boost, etc)

Returns:

an index-time normalization value

queryNorm

public float queryNorm(float sumOfSquaredWeights)

Computes the normalization value for a query given the sum of the squared weights of each of the query terms. This value is multiplied into the weight of each query term. While the classic query normalization factor is computed as 1/sqrt(sumOfSquaredWeights), other implementations might completely ignore sumOfSquaredWeights (ie return 1).

This does not affect ranking, but the default implementation does make scores from different queries more comparable than they would be by eliminating the magnitude of the Query vector as a factor in the score.

Overrides:

queryNorm in class org.apache.lucene.search.similarities.ClassicSimilarity

Parameters:

sumOfSquaredWeights - the sum of the squares of query term weights

Returns:

a normalization factor for query weights

coord

public float coord(int overlap,
                   int maxOverlap)

Computes a score factor based on the fraction of all query terms that a document contains. This value is multiplied into scores.

The presence of a large portion of the query terms indicates a better match with the query, so implementations of this method usually return larger values when the ratio between these parameters is large and smaller values when the ratio between them is small.

Overrides:

coord in class org.apache.lucene.search.similarities.ClassicSimilarity

Parameters:

overlap - the number of query terms matched in the document

maxOverlap - the total number of terms in the query

Returns:

a score factor based on term overlap with the query