Package org.apache.lucene.search.similarity

Class LegacyBM25Similarity

java.lang.Object

org.apache.lucene.search.similarities.Similarity

org.apache.lucene.search.similarity.LegacyBM25Similarity

@Deprecated
public final class LegacyBM25Similarity
extends Similarity

Deprecated.

BM25Similarity should be used instead

Similarity that behaves like BM25Similarity while also applying the k1+1 factor to the numerator of the scoring formula

See Also:

BM25Similarity

Nested Class Summary

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

Similarity.SimScorer

Constructor Summary

Constructors

Constructor	Description
LegacyBM25Similarity()	Deprecated. BM25 with these default values: k1 = 1.2 b = 0.75
LegacyBM25Similarity(float k1, float b)	Deprecated. BM25 with the supplied parameter values.

Method Summary

Modifier and Type	Method	Description
long	computeNorm(FieldInvertState state)	Deprecated. Computes the normalization value for a field, given the accumulated state of term processing for this field (see FieldInvertState).
float	getB()	Deprecated. Returns the b parameter
boolean	getDiscountOverlaps()	Deprecated. Returns true if overlap tokens are discounted from the document's length.
float	getK1()	Deprecated. Returns the k1 parameter
Similarity.SimScorer	scorer(float boost, CollectionStatistics collectionStats, TermStatistics... termStats)	Deprecated. Compute any collection-level weight (e.g.
void	setDiscountOverlaps(boolean v)	Deprecated. Sets whether overlap tokens (Tokens with 0 position increment) are ignored when computing norm.
String	toString()	Deprecated.

Methods inherited from class java.lang.Object

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

Constructor Detail

LegacyBM25Similarity

public LegacyBM25Similarity()

Deprecated.

BM25 with these default values:

• k1 = 1.2
• b = 0.75

LegacyBM25Similarity

public LegacyBM25Similarity(float k1,
                            float b)

Deprecated.

BM25 with the supplied parameter values.

Parameters:

k1 - Controls non-linear term frequency normalization (saturation).

b - Controls to what degree document length normalizes tf values.

Throws:

IllegalArgumentException - if k1 is infinite or negative, or if b is not within the range [0..1]

Method Detail

computeNorm

public long computeNorm(FieldInvertState state)

Deprecated.

Description copied from class: Similarity

Computes the normalization value for a field, given the accumulated state of term processing for this field (see FieldInvertState).

Matches in longer fields are less precise, so implementations of this method usually set smaller values when state.getLength() is large, and larger values when state.getLength() is small.

Note that for a given term-document frequency, greater unsigned norms must produce scores that are lower or equal, ie. for two encoded norms n1 and n2 so that Long.compareUnsigned(n1, n2) > 0 then SimScorer.score(freq, n1) <= SimScorer.score(freq, n2) for any legal freq.

0 is not a legal norm, so 1 is the norm that produces the highest scores.

Specified by:

computeNorm in class Similarity

Parameters:

state - current processing state for this field

Returns:

computed norm value

scorer

public Similarity.SimScorer scorer(float boost,
                                   CollectionStatistics collectionStats,
                                   TermStatistics... termStats)

Deprecated.

Description copied from class: Similarity

Compute any collection-level weight (e.g. IDF, average document length, etc) needed for scoring a query.

Specified by:

scorer in class Similarity

Parameters:

boost - a multiplicative factor to apply to the produces scores

collectionStats - collection-level statistics, such as the number of tokens in the collection.

termStats - term-level statistics, such as the document frequency of a term across the collection.

Returns:

SimWeight object with the information this Similarity needs to score a query.

getK1

public final float getK1()

Deprecated.

Returns the k1 parameter

See Also:

LegacyBM25Similarity(float, float)

getB

public final float getB()

Deprecated.

Returns the b parameter

See Also:

LegacyBM25Similarity(float, float)

setDiscountOverlaps

public void setDiscountOverlaps(boolean v)

Deprecated.

Sets whether overlap tokens (Tokens with 0 position increment) are ignored when computing norm. By default this is true, meaning overlap tokens do not count when computing norms.

getDiscountOverlaps

public boolean getDiscountOverlaps()

Deprecated.

Returns true if overlap tokens are discounted from the document's length.

See Also:

setDiscountOverlaps(boolean)

toString

public String toString()

Deprecated.

Overrides:

toString in class Object