DFR_BM25 (Terrier Information Retrieval Platform 5.5 API)

java.lang.Object
- org.terrier.matching.models.WeightingModel
- - org.terrier.matching.models.DFR_BM25

All Implemented Interfaces:

java.io.Serializable, java.lang.Cloneable, Model
```
public class DFR_BM25
extends WeightingModel
```
This class implements the DFR_BM25 weighting model. This DFR model, if expanded in Taylor's series, provides the BM25 formula, when the parameter c is set to 1.

Author:

Gianni Amati, Ben He

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

DFR_BM25()
A default constructor.

DFR_BM25(double c)
Constructs an instance of this class with the specified value for the parameter c.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`java.lang.String`	`getInfo()`	Returns the name of the model.
`double`	`score(double tf, double docLength)`	Computes the score according to the model DFR_BM25.

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
  - DFR_BM25
```
public DFR_BM25()
```
    A default constructor. This must be followed by specifying the c value.
  - DFR_BM25
```
public DFR_BM25(double c)
```
    Constructs an instance of this class with the specified value for the parameter c.
    
    Parameters:
    
    c - the term frequency normalisation parameter value.
- Method Detail
  - getInfo
```
public final java.lang.String getInfo()
```
    Returns the name of the model.
    
    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)
```
    Computes the score according to the model DFR_BM25.
    
    Specified by:
    
    score in class WeightingModel
    
    Parameters:
    
    tf - The term frequency 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