Package org.apache.lucene.search

Class BayesianScoreQuery

java.lang.Object
org.apache.lucene.search.Query
org.apache.lucene.search.BayesianScoreQuery
public final class BayesianScoreQuery extends Query
A query wrapper that transforms the inner query's score into a calibrated probability via sigmoid calibration: P = sigmoid(alpha * (score - beta)).

This implements the query-level Bayesian transform from "Bayesian BM25": the inner query (typically a multi-term BooleanQuery with BM25Similarity) produces a raw score, and this wrapper maps it to a probability in (0, 1) suitable for combination with other probability signals via LogOddsFusionQuery.

The alpha parameter controls the sigmoid steepness (score sensitivity), and beta controls the midpoint (decision boundary). These can be set manually or estimated from the score distribution via BayesianScoreEstimator.

An optional base rate encodes the corpus-level prior probability that a random document is relevant to a random query. When set, the posterior is computed in log-odds space: sigmoid(alpha * (score - beta) + logit(baseRate)). This shifts scores down for rare-relevance corpora, improving calibration.

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

  • Constructor Details

    • BayesianScoreQuery

      public BayesianScoreQuery(Query query, float alpha, float beta, float baseRate)
      Creates a BayesianScoreQuery with base rate.
      Parameters:
      query - the inner query whose scores will be transformed
      alpha - sigmoid steepness (must be positive and finite)
      beta - sigmoid midpoint (must be finite)
      baseRate - corpus-level relevance prior in (0, 1), or 0 to disable. When positive, adds logit(baseRate) to the log-odds before sigmoid, shifting scores to account for the rarity of relevant documents.

    • BayesianScoreQuery

      public BayesianScoreQuery(Query query, float alpha, float beta)
      Creates a BayesianScoreQuery without base rate.
      Parameters:
      query - the inner query whose scores will be transformed
      alpha - sigmoid steepness (must be positive and finite)
      beta - sigmoid midpoint (must be finite)

  • Method Details

    • getQuery

      public Query getQuery()
      Returns the wrapped query.

    • getAlpha

      public float getAlpha()
      Returns the sigmoid steepness parameter.

    • getBeta

      public float getBeta()
      Returns the sigmoid midpoint parameter.

    • getBaseRate

      public float getBaseRate()
      Returns the base rate, or 0 if not set.

    • createWeight

      public Weight createWeight(IndexSearcher searcher, ScoreMode scoreMode, float boost) throws IOException
      Description copied from class: Query
      Expert: Constructs an appropriate Weight implementation for this query.

      Only implemented by primitive queries, which re-write to themselves.

      Overrides:
      createWeight in class Query
      Parameters:
      scoreMode - How the produced scorers will be consumed.
      boost - The boost that is propagated by the parent queries.
      Throws:
      IOException

    • rewrite

      public Query rewrite(IndexSearcher indexSearcher) throws IOException
      Description copied from class: Query
      Expert: called to re-write queries into primitive queries. For example, a PrefixQuery will be rewritten into a BooleanQuery that consists of TermQuerys.

      Callers are expected to call rewrite multiple times if necessary, until the rewritten query is the same as the original query.

      The rewrite process may be able to make use of IndexSearcher's executor and be executed in parallel if the executor is provided.

      Overrides:
      rewrite in class Query
      Throws:
      IOException
      See Also:

    • visit

      public void visit(QueryVisitor visitor)
      Description copied from class: Query
      Recurse through the query tree, visiting any child queries.
      Specified by:
      visit in class Query
      Parameters:
      visitor - a QueryVisitor to be called by each query in the tree

    • toString

      public String toString(String field)
      Description copied from class: Query
      Prints a query to a string, with field assumed to be the default field and omitted.
      Specified by:
      toString in class Query

    • equals

      public boolean equals(Object other)
      Description copied from class: Query
      Override and implement query instance equivalence properly in a subclass. This is required so that QueryCache works properly.

      Typically a query will be equal to another only if it's an instance of the same class and its document-filtering properties are identical to those of the other instance. Utility methods are provided for certain repetitive code.

      Specified by:
      equals in class Query
      See Also:

    • hashCode

      public int hashCode()
      Description copied from class: Query
      Override and implement query hash code properly in a subclass. This is required so that QueryCache works properly.
      Specified by:
      hashCode in class Query
      See Also: