This class implements the DPH weighting scheme. More...

#include <weight.h>

Inheritance diagram for Xapian::DPHWeight:

Collaboration diagram for Xapian::DPHWeight:

Public Member Functions
	DPHWeight ()
	Construct a DPHWeight. More...

std::string	name () const
	Return the name of this weighting scheme. More...

std::string	serialise () const
	Return this object's parameters serialised as a single string. More...

DPHWeight *	unserialise (const std::string &serialised) const
	Unserialise parameters. More...

double	get_sumpart (Xapian::termcount wdf, Xapian::termcount doclen, Xapian::termcount uniqterms) const
	Calculate the weight contribution for this object's term to a document. More...

double	get_maxpart () const
	Return an upper bound on what get_sumpart() can return for any document. More...

double	get_sumextra (Xapian::termcount doclen, Xapian::termcount uniqterms) const
	Calculate the term-independent weight component for a document. More...

double	get_maxextra () const
	Return an upper bound on what get_sumextra() can return for any document. More...

Public Member Functions inherited from Xapian::Weight
	Weight ()
	Default constructor, needed by subclass constructors. More...

virtual	~Weight ()
	Virtual destructor, because we have virtual methods. More...

Private Member Functions
DPHWeight *	clone () const
	Clone this object. More...

void	init (double factor)
	Allow the subclass to perform any initialisation it needs to. More...

Private Attributes
double	upper_bound
	The upper bound on the weight. More...

double	lower_bound
	Now unused but left in place in 1.4.x for ABI compatibility. More...

double	log_constant
	The constant value used in get_sumpart() . More...

double	wqf_product_factor

Additional Inherited Members
Public Types inherited from Xapian::Weight
enum	type_smoothing { TWO_STAGE_SMOOTHING = 1, DIRICHLET_SMOOTHING = 2, ABSOLUTE_DISCOUNT_SMOOTHING = 3, JELINEK_MERCER_SMOOTHING = 4, DIRICHLET_PLUS_SMOOTHING = 5 }
	Type of smoothing to use with the Language Model Weighting scheme. More...

Protected Types inherited from Xapian::Weight
enum	stat_flags { COLLECTION_SIZE = 1, RSET_SIZE = 2, AVERAGE_LENGTH = 4, TERMFREQ = 8, RELTERMFREQ = 16, QUERY_LENGTH = 32, WQF = 64, WDF = 128, DOC_LENGTH = 256, DOC_LENGTH_MIN = 512, DOC_LENGTH_MAX = 1024, WDF_MAX = 2048, COLLECTION_FREQ = 4096, UNIQUE_TERMS = 8192, TOTAL_LENGTH = COLLECTION_SIZE \| AVERAGE_LENGTH }
	Stats which the weighting scheme can use (see need_stat()). More...

Protected Member Functions inherited from Xapian::Weight
void	need_stat (stat_flags flag)
	Tell Xapian that your subclass will want a particular statistic. More...

	Weight (const Weight &)
	Don't allow copying. More...

Xapian::doccount	get_collection_size () const
	The number of documents in the collection. More...

Xapian::doccount	get_rset_size () const
	The number of documents marked as relevant. More...

Xapian::doclength	get_average_length () const
	The average length of a document in the collection. More...

Xapian::doccount	get_termfreq () const
	The number of documents which this term indexes. More...

Xapian::doccount	get_reltermfreq () const
	The number of relevant documents which this term indexes. More...

Xapian::termcount	get_collection_freq () const
	The collection frequency of the term. More...

Xapian::termcount	get_query_length () const
	The length of the query. More...

Xapian::termcount	get_wqf () const
	The within-query-frequency of this term. More...

Xapian::termcount	get_doclength_upper_bound () const
	An upper bound on the maximum length of any document in the database. More...

Xapian::termcount	get_doclength_lower_bound () const
	A lower bound on the minimum length of any document in the database. More...

Xapian::termcount	get_wdf_upper_bound () const
	An upper bound on the wdf of this term. More...

Xapian::totallength	get_total_length () const
	Total length of all documents in the collection. More...

Detailed Description

This class implements the DPH weighting scheme.

DPH is a representative scheme of the Divergence from Randomness Framework by Gianni Amati.

This is a parameter free weighting scheme and it should be used with query expansion to obtain better results. It uses the HyperGeometric Probabilistic model and Popper's normalization to calculate the risk gain.

For more information about the DFR Framework and the DPH scheme, please refer to : a.) Gianni Amati and Cornelis Joost Van Rijsbergen Probabilistic models of information retrieval based on measuring the divergence from randomness ACM Transactions on Information Systems (TOIS) 20, (4), 2002, pp. 357-389. b.) FUB, IASI-CNR and University of Tor Vergata at TREC 2007 Blog Track. G. Amati and E. Ambrosi and M. Bianchi and C. Gaibisso and G. Gambosi. Proceedings of the 16th Text Retrieval Conference (TREC-2007), 2008.

Definition at line 1348 of file weight.h.

Constructor & Destructor Documentation

◆ DPHWeight()

Xapian::DPHWeight::DPHWeight ( )

inline

Construct a DPHWeight.

Definition at line 1365 of file weight.h.

References name.

Member Function Documentation

◆ clone()

DPHWeight * Xapian::DPHWeight::clone ( ) const

privatevirtual

Clone this object.

This method allocates and returns a copy of the object it is called on.

If your subclass is called FooWeight and has parameters a and b, then you would implement FooWeight::clone() like so:

FooWeight * FooWeight::clone() const { return new FooWeight(a, b); }

Note that the returned object will be deallocated by Xapian after use with "delete". If you want to handle the deletion in a special way (for example when wrapping the Xapian API for use from another language) then you can define a static operator delete method in your subclass as shown here: https://trac.xapian.org/ticket/554#comment:1

Implements Xapian::Weight.

Definition at line 36 of file dphweight.cc.

◆ get_maxextra()

double Xapian::DPHWeight::get_maxextra ( ) const

virtual

Return an upper bound on what get_sumextra() can return for any document.

This information is used by the matcher to perform various optimisations, so strive to make the bound as tight as possible.

Implements Xapian::Weight.

Definition at line 168 of file dphweight.cc.

◆ get_maxpart()

double Xapian::DPHWeight::get_maxpart ( ) const

virtual

Return an upper bound on what get_sumpart() can return for any document.

This information is used by the matcher to perform various optimisations, so strive to make the bound as tight as possible.

Implements Xapian::Weight.

Definition at line 156 of file dphweight.cc.

◆ get_sumextra()

double Xapian::DPHWeight::get_sumextra	(	Xapian::termcount	doclen,
		Xapian::termcount	uniqterms
	)		const

virtual

Calculate the term-independent weight component for a document.

The parameter gives information about the document which may be used in the calculations:

Parameters

doclen	The document's length (unnormalised).
uniqterms	The number of unique terms in the document.

Implements Xapian::Weight.

Definition at line 162 of file dphweight.cc.

◆ get_sumpart()

double Xapian::DPHWeight::get_sumpart	(	Xapian::termcount	wdf,
		Xapian::termcount	doclen,
		Xapian::termcount	uniqterms
	)		const

virtual

Calculate the weight contribution for this object's term to a document.

The parameters give information about the document which may be used in the calculations:

Parameters

wdf	The within document frequency of the term in the document.
doclen	The document's length (unnormalised).
uniqterms	Number of unique terms in the document (used for absolute smoothing).

Implements Xapian::Weight.

Definition at line 137 of file dphweight.cc.

References log2(), and rare.

◆ init()

void Xapian::DPHWeight::init ( double factor )

privatevirtual

Allow the subclass to perform any initialisation it needs to.

Parameters

factor Any scaling factor (e.g. from OP_SCALE_WEIGHT). If the Weight object is for the term-independent weight supplied by get_sumextra()/get_maxextra(), then init(0.0) is called (starting from Xapian 1.2.11 and 1.3.1 - earlier versions failed to call init() for such Weight objects).

Implements Xapian::Weight.

Definition at line 42 of file dphweight.cc.

References log2(), and rare.

◆ name()

string Xapian::DPHWeight::name ( ) const

virtual

Return the name of this weighting scheme.

This name is used by the remote backend. It is passed along with the serialised parameters to the remote server so that it knows which class to create.

Return the full namespace-qualified name of your class here - if your class is called FooWeight, return "FooWeight" from this method (Xapian::BM25Weight returns "Xapian::BM25Weight" here).

If you don't want to support the remote backend, you can use the default implementation which simply returns an empty string.

Reimplemented from Xapian::Weight.

Definition at line 117 of file dphweight.cc.

Referenced by DEFINE_TESTCASE().

◆ serialise()

string Xapian::DPHWeight::serialise ( ) const

virtual

Return this object's parameters serialised as a single string.

If you don't want to support the remote backend, you can use the default implementation which simply throws Xapian::UnimplementedError.

Reimplemented from Xapian::Weight.

Definition at line 123 of file dphweight.cc.

Referenced by DEFINE_TESTCASE().

◆ unserialise()

DPHWeight * Xapian::DPHWeight::unserialise ( const std::string & serialised ) const

virtual

Unserialise parameters.

This method unserialises parameters serialised by the serialise() method and allocates and returns a new object initialised with them.

If you don't want to support the remote backend, you can use the default implementation which simply throws Xapian::UnimplementedError.

Note that the returned object will be deallocated by Xapian after use with "delete". If you want to handle the deletion in a special way (for example when wrapping the Xapian API for use from another language) then you can define a static operator delete method in your subclass as shown here: https://trac.xapian.org/ticket/554#comment:1

Parameters

serialised A string containing the serialised parameters.

Reimplemented from Xapian::Weight.

Definition at line 129 of file dphweight.cc.

References rare.

Referenced by DEFINE_TESTCASE().

Member Data Documentation

◆ log_constant

double Xapian::DPHWeight::log_constant

private

The constant value used in get_sumpart() .

Definition at line 1356 of file weight.h.

◆ lower_bound

double Xapian::DPHWeight::lower_bound

private

Now unused but left in place in 1.4.x for ABI compatibility.

Definition at line 1353 of file weight.h.

◆ upper_bound

double Xapian::DPHWeight::upper_bound

private

The upper bound on the weight.

Definition at line 1350 of file weight.h.

◆ wqf_product_factor

double Xapian::DPHWeight::wqf_product_factor

private

Definition at line 1357 of file weight.h.

The documentation for this class was generated from the following files:

include/xapian/weight.h
weight/dphweight.cc

Public Member Functions

Private Member Functions

Private Attributes

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

◆ DPHWeight()

Member Function Documentation

◆ clone()

◆ get_maxextra()

◆ get_maxpart()

◆ get_sumextra()

◆ get_sumpart()

◆ init()

◆ name()

◆ serialise()

◆ unserialise()

Member Data Documentation

◆ log_constant

◆ lower_bound

◆ upper_bound

◆ wqf_product_factor