org.apache.lucene.search.postingshighlight

Class PassageScorer

    • Constructor Summary

      Constructors 
      Constructor and Description
      PassageScorer()
      Creates PassageScorer with these default values: k1 = 1.2, b = 0.75.
      PassageScorer(float k1, float b, float pivot)
      Creates PassageScorer with specified scoring parameters
    • Constructor Detail

      • PassageScorer

        public PassageScorer()
        Creates PassageScorer with these default values:
        • k1 = 1.2,
        • b = 0.75.
        • pivot = 87
      • PassageScorer

        public PassageScorer(float k1,
                             float b,
                             float pivot)
        Creates PassageScorer with specified scoring parameters
        Parameters:
        k1 - Controls non-linear term frequency normalization (saturation).
        b - Controls to what degree passage length normalizes tf values.
        pivot - Pivot value for length normalization (some rough idea of average sentence length in characters).
    • Method Detail

      • weight

        public float weight(int contentLength,
                            int totalTermFreq)
        Computes term importance, given its in-document statistics.
        Parameters:
        contentLength - length of document in characters
        totalTermFreq - number of time term occurs in document
        Returns:
        term importance
      • tf

        public float tf(int freq,
                        int passageLen)
        Computes term weight, given the frequency within the passage and the passage's length.
        Parameters:
        freq - number of occurrences of within this passage
        passageLen - length of the passage in characters.
        Returns:
        term weight
      • norm

        public float norm(int passageStart)
        Normalize a passage according to its position in the document.

        Typically passages towards the beginning of the document are more useful for summarizing the contents.

        The default implementation is 1 + 1/log(pivot + passageStart)

        Parameters:
        passageStart - start offset of the passage
        Returns:
        a boost value multiplied into the passage's core.