Class PerFieldSimilarityWrapper


public abstract class PerFieldSimilarityWrapper extends Similarity
Provides the ability to use a different Similarity for different fields.

Subclasses should implement get(String) to return an appropriate Similarity (for example, using field-specific parameter values) for the field.

WARNING: This API is experimental and might change in incompatible ways in the next release.
  • Constructor Details

    • PerFieldSimilarityWrapper

      public PerFieldSimilarityWrapper()
      Sole constructor. (For invocation by subclass constructors, typically implicit.)
  • Method Details

    • computeNorm

      public final 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.

      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
      state - current processing state for this field
      computed norm value
    • scorer

      public final 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
      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.
      SimWeight object with the information this Similarity needs to score a query.
    • get

      public abstract Similarity get(String name)
      Returns a Similarity for scoring a field.