org.terrier.matching.models
Class DFRee

java.lang.Object
  org.terrier.matching.models.WeightingModel
      org.terrier.matching.models.DFRee

All Implemented Interfaces:

java.io.Serializable, java.lang.Cloneable, Model

public class DFRee
extends WeightingModel

This class implements the DFRee weighting model. DFRee stands for DFR free from parameters. In particular, the DFRee model computes an average number of extra bits (as information divergence) that are necessary to code one extra token of the query term with respect to the probability distribution observed in the document. There are two possible populations to sample the probability distribution: considering only the document and no other document in the colection, or the document considered as sample drawn from the entire collection statistics. DFRee takes an average of these two information measures, that is their inner product.

Author:

Gianni Amati

See Also:

Serialized Form

Field Summary

Fields inherited from class org.terrier.matching.models.WeightingModel

averageDocumentLength, c, documentFrequency, i, keyFrequency, numberOfDocuments, numberOfPointers, numberOfTokens, numberOfUniqueTerms, termFrequency

Constructor Summary

DFRee()
A default constructor to make this model.

Method Summary

java.lang.String	getInfo() Returns the name of the model, in this case "DFRee"
double	score(double tf, double docLength) Uses DFRee to compute a weight for a term in a document.
double	score(double tf, double docLength, double documentFrequency, double termFrequency, double keyFrequency) Uses DFRee to compute a weight for a term in a document.

Methods inherited from class org.terrier.matching.models.WeightingModel

clone, getOverflowed, getParameter, prepare, score, setAverageDocumentLength, setCollectionStatistics, setDocumentFrequency, setEntryStatistics, setKeyFrequency, setNumberOfDocuments, setNumberOfPointers, setNumberOfTokens, setNumberOfUniqueTerms, setParameter, setRequest, setTermFrequency, stirlingPower

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DFRee

public DFRee()

A default constructor to make this model.

Method Detail

getInfo

public final java.lang.String getInfo()

Returns the name of the model, in this case "DFRee"

Specified by:

getInfo in interface Model

Specified by:

getInfo in class WeightingModel

Returns:

the name of the model

score

public final double score(double tf,
                          double docLength)

Uses DFRee to compute a weight for a term in a document.

Specified by:

score in class WeightingModel

Parameters:

tf - The term frequency of the term in the document

docLength - the document's length

Returns:

the score assigned to a document with the given tf and docLength, and other preset parameters

score

public final double score(double tf,
                          double docLength,
                          double documentFrequency,
                          double termFrequency,
                          double keyFrequency)

Uses DFRee to compute a weight for a term in a document.

Specified by:

score in class WeightingModel

Parameters:

tf - The term frequency of the term in the document

docLength - the document's length

documentFrequency - The document frequency of the term (ignored)

termFrequency - the term frequency in the collection (ignored)

keyFrequency - the term frequency in the query (ignored).

Returns:

the score assigned by the weighting model DFRee.