org.apache.lucene.search
Class DefaultSimilarity

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

All Implemented Interfaces:

Serializable

public class DefaultSimilarity
extends Similarity

Expert: Default scoring implementation.

See Also:

Serialized Form

Field Summary

protected boolean

discountOverlaps

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

NO_DOC_ID_PROVIDED

Constructor Summary

DefaultSimilarity()

Method Summary

float	computeNorm(String field, FieldInvertState state) Implemented as state.getBoost()*lengthNorm(numTerms), where numTerms is FieldInvertState.getLength() if setDiscountOverlaps(boolean) is false, else it's FieldInvertState.getLength() - FieldInvertState.getNumOverlap().
float	coord(int overlap, int maxOverlap) Implemented as overlap / maxOverlap.
boolean	getDiscountOverlaps()
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).
void	setDiscountOverlaps(boolean v) Determines whether overlap tokens (Tokens with 0 position increment) are ignored when computing norm.
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, idfExplain, idfExplain, scorePayload, setDefault, tf

Methods inherited from class java.lang.Object

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

Field Detail

discountOverlaps

protected boolean discountOverlaps

Constructor Detail

DefaultSimilarity

public DefaultSimilarity()

Method Detail

computeNorm

public float computeNorm(String field,
                         FieldInvertState state)

Implemented as state.getBoost()*lengthNorm(numTerms), where numTerms is FieldInvertState.getLength() if setDiscountOverlaps(boolean) is false, else it's FieldInvertState.getLength() - FieldInvertState.getNumOverlap().

WARNING: This API is new and experimental, and may suddenly change.

Overrides:

computeNorm in class Similarity

Parameters:

field - field name

state - current processing state for this field

Returns:

the calculated float norm

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

setDiscountOverlaps

public void setDiscountOverlaps(boolean v)

Determines whether overlap tokens (Tokens with 0 position increment) are ignored when computing norm. By default this is false, meaning overlap tokens are counted just like non-overlap tokens.

WARNING: This API is new and experimental, and may suddenly change.

See Also:

computeNorm(java.lang.String, org.apache.lucene.index.FieldInvertState)

getDiscountOverlaps

public boolean getDiscountOverlaps()

See Also:

setDiscountOverlaps(boolean)