Package org.apache.lucene.search.similarities

Class 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.

    • 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 at index-time.

        The default implementation uses SmallFloat.intToByte4(int) to encode the number of terms as a single byte.

        WARNING: The default implementation is used by Lucene's supplied Similarity classes, which means you can change the Similarity at runtime without reindexing. If you override this method, you'll need to re-index documents for it to take effect.

        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.

        Overrides:
        computeNorm in class Similarity
        Parameters:
        state - accumulated state of term processing for this field
        Returns:
        computed norm value

      • scorer

        public Similarity.SimScorer scorer​(float boost,
                                   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:
        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.