org.apache.lucene.search.similarities
Class MultiSimilarity

java.lang.Object
  extended by org.apache.lucene.search.similarities.Similarity
      extended by org.apache.lucene.search.similarities.MultiSimilarity

public class MultiSimilarity
extends Similarity

Implements the CombSUM method for combining evidence from multiple similarity values described in: Joseph A. Shaw, Edward A. Fox. In Text REtrieval Conference (1993), pp. 243-252

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.ExactSimScorer, Similarity.SimWeight, Similarity.SloppySimScorer
 
Field Summary
protected  Similarity[] sims
          the sub-similarities used to create the combined score
 
Constructor Summary
MultiSimilarity(Similarity[] sims)
          Creates a MultiSimilarity which will sum the scores of the provided sims.
 
Method Summary
 long computeNorm(FieldInvertState state)
          Computes the normalization value for a field, given the accumulated state of term processing for this field (see FieldInvertState).
 Similarity.SimWeight computeWeight(float queryBoost, CollectionStatistics collectionStats, TermStatistics... termStats)
          Compute any collection-level weight (e.g.
 Similarity.ExactSimScorer exactSimScorer(Similarity.SimWeight stats, AtomicReaderContext context)
          Creates a new Similarity.ExactSimScorer to score matching documents from a segment of the inverted index.
 Similarity.SloppySimScorer sloppySimScorer(Similarity.SimWeight stats, AtomicReaderContext context)
          Creates a new Similarity.SloppySimScorer to score matching documents from a segment of the inverted index.
 
Methods inherited from class org.apache.lucene.search.similarities.Similarity
coord, queryNorm
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

sims

protected final Similarity[] sims
the sub-similarities used to create the combined score

Constructor Detail

MultiSimilarity

public MultiSimilarity(Similarity[] sims)
Creates a MultiSimilarity which will sum the scores of the provided sims.

Method Detail

computeNorm

public long computeNorm(FieldInvertState state)
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.

Specified by:
computeNorm in class Similarity
Parameters:
state - current processing state for this field
Returns:
computed norm value

computeWeight

public Similarity.SimWeight computeWeight(float queryBoost,
                                          CollectionStatistics collectionStats,
                                          TermStatistics... termStats)
Description copied from class: Similarity
Compute any collection-level weight (e.g. IDF, average document length, etc) needed for scoring a query.

Specified by:
computeWeight in class Similarity
Parameters:
queryBoost - the query-time boost.
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.

exactSimScorer

public Similarity.ExactSimScorer exactSimScorer(Similarity.SimWeight stats,
                                                AtomicReaderContext context)
                                         throws IOException
Description copied from class: Similarity
Creates a new Similarity.ExactSimScorer to score matching documents from a segment of the inverted index.

Specified by:
exactSimScorer in class Similarity
Parameters:
stats - collection information from Similarity.computeWeight(float, CollectionStatistics, TermStatistics...)
context - segment of the inverted index to be scored.
Returns:
ExactSimScorer for scoring documents across context
Throws:
IOException - if there is a low-level I/O error

sloppySimScorer

public Similarity.SloppySimScorer sloppySimScorer(Similarity.SimWeight stats,
                                                  AtomicReaderContext context)
                                           throws IOException
Description copied from class: Similarity
Creates a new Similarity.SloppySimScorer to score matching documents from a segment of the inverted index.

Specified by:
sloppySimScorer in class Similarity
Parameters:
stats - collection information from Similarity.computeWeight(float, CollectionStatistics, TermStatistics...)
context - segment of the inverted index to be scored.
Returns:
SloppySimScorer for scoring documents across context
Throws:
IOException - if there is a low-level I/O error


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