Class Bo2


  • public class Bo2
    extends QueryExpansionModel
    This class implements the Bo2 model for query expansion. See G. Amati's Phd Thesis.
    Author:
    Gianni Amati, Ben He
    • Constructor Detail

      • Bo2

        public Bo2()
        A default constructor.
    • Method Detail

      • getInfo

        public final java.lang.String getInfo()
        Returns the name of the model.
        Specified by:
        getInfo in class QueryExpansionModel
        Returns:
        the name of the model
      • parameterFreeNormaliser

        public final double parameterFreeNormaliser()
        This method computes the normaliser of parameter-free query expansion.
        Specified by:
        parameterFreeNormaliser in class QueryExpansionModel
        Returns:
        The normaliser.
      • parameterFreeNormaliser

        public final double parameterFreeNormaliser​(double maxTermFrequency,
                                                    double collectionLength,
                                                    double totalDocumentLength)
        This method computes the normaliser of parameter-free query expansion.
        Specified by:
        parameterFreeNormaliser in class QueryExpansionModel
        Parameters:
        maxTermFrequency - The maximum of the term frequency of the query terms.
        collectionLength - The number of tokens in the collections.
        totalDocumentLength - The sum of the length of the top-ranked documents.
        Returns:
        The normaliser.
      • score

        public final double score​(double withinDocumentFrequency,
                                  double termFrequency)
        This method implements the query expansion model.
        Specified by:
        score in class QueryExpansionModel
        Parameters:
        withinDocumentFrequency - double The term frequency in the X top-retrieved documents.
        termFrequency - double The term frequency in the collection.
        Returns:
        double The query expansion weight using the Bose-Einstein statistics where the mean is given by the Bernoulli process.
      • score

        public final double score​(double withinDocumentFrequency,
                                  double termFrequency,
                                  double totalDocumentLength,
                                  double collectionLength,
                                  double averageDocumentLength)
        This method implements the query expansion model.
        Specified by:
        score in class QueryExpansionModel
        Parameters:
        withinDocumentFrequency - double The term frequency in the X top-retrieved documents.
        termFrequency - double The term frequency in the collection.
        totalDocumentLength - double The sum of length of the X top-retrieved documents.
        collectionLength - double The number of tokens in the whole collection.
        averageDocumentLength - double The average document length in the collection.
        Returns:
        double The score returned by the implemented model.