org.apache.lucene.search
Class DefaultSimilarity

java.lang.Object
  org.apache.lucene.search.Similarity
      org.apache.lucene.search.DefaultSimilarity

All Implemented Interfaces:

Serializable

Direct Known Subclasses:

SweetSpotSimilarity

public class DefaultSimilarity
extends Similarity

Expert: Default scoring implementation.

See Also:

Serialized Form

Constructor Summary

DefaultSimilarity()

Method Summary

float	coord(int overlap, int maxOverlap) Implemented as overlap / maxOverlap.
float	idf(int docFreq, int numDocs) Implemented as log(numDocs/(docFreq+1)) + 1.
float	lengthNorm(String fieldName, int numTerms) Implemented as 1/sqrt(numTerms).
float	queryNorm(float sumOfSquaredWeights) Implemented as 1/sqrt(sumOfSquaredWeights).
float	sloppyFreq(int distance) Implemented as 1 / (distance + 1).
float	tf(float freq) Implemented as sqrt(freq).

Methods inherited from class org.apache.lucene.search.Similarity

decodeNorm, encodeNorm, getDefault, getNormDecoder, idf, idf, scorePayload, setDefault, tf

Methods inherited from class java.lang.Object

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

Constructor Detail

DefaultSimilarity

public DefaultSimilarity()

Method Detail

lengthNorm

public float lengthNorm(String fieldName,
                        int numTerms)

Implemented as 1/sqrt(numTerms).

Specified by:

lengthNorm in class Similarity

Parameters:

fieldName - the name of the field

numTerms - the total number of tokens contained in fields named fieldName of doc.

Returns:

a normalization factor for hits on this field of this document

See Also:

AbstractField.setBoost(float)

queryNorm

public float queryNorm(float sumOfSquaredWeights)

Implemented as 1/sqrt(sumOfSquaredWeights).

Specified by:

queryNorm in class Similarity

Parameters:

sumOfSquaredWeights - the sum of the squares of query term weights

Returns:

a normalization factor for query weights

tf

public float tf(float freq)

Implemented as sqrt(freq).

Specified by:

tf in class Similarity

Parameters:

freq - the frequency of a term within a document

Returns:

a score factor based on a term's within-document frequency

sloppyFreq

public float sloppyFreq(int distance)

Implemented as 1 / (distance + 1).

Specified by:

sloppyFreq in class Similarity

Parameters:

distance - the edit distance of this sloppy phrase match

Returns:

the frequency increment for this match

See Also:

PhraseQuery.setSlop(int)

idf

public float idf(int docFreq,
                 int numDocs)

Implemented as log(numDocs/(docFreq+1)) + 1.

Specified by:

idf in class Similarity

Parameters:

docFreq - the number of documents which contain the term

numDocs - the total number of documents in the collection

Returns:

a score factor based on the term's document frequency

coord

public float coord(int overlap,
                   int maxOverlap)

Implemented as overlap / maxOverlap.

Specified by:

coord in class Similarity

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