DFRee (Terrier Information Retrieval Platform 5.5 API)

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

Constructor Summary

Constructors
Constructor Description

DFRee()
A default constructor to make this model.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`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.

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 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