org.terrier.matching.models

Class DFRee

java.lang.Object

org.terrier.matching.models.WeightingModel

org.terrier.matching.models.DFRee

All Implemented Interfaces:

Serializable, 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, cs, documentFrequency, es, i, keyFrequency, numberOfDocuments, numberOfPointers, numberOfTokens, numberOfUniqueTerms, rq, termFrequency

Constructor Summary

Constructors

Constructor and Description
DFRee() A default constructor to make this model.

Method Summary

Methods

Modifier and Type	Method and Description
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) Deprecated.

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

clone, getOverflowed, getParameter, prepare, score, setCollectionStatistics, setEntryStatistics, setKeyFrequency, setParameter, setRequest

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 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

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

Deprecated.

This method provides the contract for implementing weighting models. As of Terrier 3.6, the 5-parameter score method is being deprecated since it is not used. The two parameter score method should be used instead. Tagged for removal in a later version.

Specified by:

score in class WeightingModel

Parameters:

tf - The term frequency in the document

docLength - the document's length

documentFrequency - The document frequency of the term

termFrequency - the term frequency in the collection

keyFrequency - the term frequency in the query

Returns:

the score returned by the implemented weighting model.