xapian-core  1.4.20
Public Member Functions | Private Member Functions | Private Attributes | List of all members
Xapian::InL2Weight Class Reference

This class implements the InL2 weighting scheme. More...

#include <weight.h>

+ Inheritance diagram for Xapian::InL2Weight:
+ Collaboration diagram for Xapian::InL2Weight:

Public Member Functions

 InL2Weight (double c)
 Construct an InL2Weight. More...
 
 InL2Weight ()
 
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...
 
InL2Weightunserialise (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

InL2Weightclone () const
 Clone this object. More...
 
void init (double factor)
 Allow the subclass to perform any initialisation it needs to. More...
 

Private Attributes

double param_c
 The wdf normalization parameter in the formula. More...
 
double upper_bound
 The upper bound on the weight a term can give to a document. More...
 
double wqf_product_idf
 The constant values which are used on every call to get_sumpart(). More...
 
double c_product_avlen
 

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 InL2 weighting scheme.

InL2 is a representative scheme of the Divergence from Randomness Framework by Gianni Amati.

This weighting scheme is useful for tasks that require early precision.

It uses the Inverse document frequency model (In), the Laplace method to find the aftereffect of sampling (L) and the second wdf normalization proposed by Amati to normalize the wdf in the document to the length of the document (H2).

For more information about the DFR Framework and the InL2 scheme, please refer to: 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.

Definition at line 838 of file weight.h.

Constructor & Destructor Documentation

◆ InL2Weight() [1/2]

Xapian::InL2Weight::InL2Weight ( double  c)
explicit

Construct an InL2Weight.

Parameters
cA strictly positive parameter controlling the extent of the normalization of the wdf to the document length. The default value of 1 is suitable for longer queries but it may need to be changed for shorter queries. For more information, please refer to Gianni Amati's PHD thesis.

Definition at line 34 of file inl2weight.cc.

References Xapian::Weight::AVERAGE_LENGTH, Xapian::Weight::COLLECTION_SIZE, Xapian::Weight::DOC_LENGTH, Xapian::Weight::DOC_LENGTH_MIN, Xapian::Weight::need_stat(), param_c, Xapian::Weight::TERMFREQ, Xapian::Weight::WDF, Xapian::Weight::WDF_MAX, and Xapian::Weight::WQF.

◆ InL2Weight() [2/2]

Xapian::InL2Weight::InL2Weight ( )
inline

Definition at line 864 of file weight.h.

References name.

Referenced by clone(), and unserialise().

Member Function Documentation

◆ clone()

InL2Weight * Xapian::InL2Weight::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 50 of file inl2weight.cc.

References InL2Weight(), and param_c.

◆ get_maxextra()

double Xapian::InL2Weight::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 140 of file inl2weight.cc.

◆ get_maxpart()

double Xapian::InL2Weight::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 128 of file inl2weight.cc.

References upper_bound.

◆ get_sumextra()

double Xapian::InL2Weight::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
doclenThe document's length (unnormalised).
uniqtermsThe number of unique terms in the document.

Implements Xapian::Weight.

Definition at line 134 of file inl2weight.cc.

◆ get_sumpart()

double Xapian::InL2Weight::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
wdfThe within document frequency of the term in the document.
doclenThe document's length (unnormalised).
uniqtermsNumber of unique terms in the document (used for absolute smoothing).

Implements Xapian::Weight.

Definition at line 114 of file inl2weight.cc.

References c_product_avlen, log2(), and wqf_product_idf.

◆ init()

void Xapian::InL2Weight::init ( double  factor)
privatevirtual

Allow the subclass to perform any initialisation it needs to.

Parameters
factorAny 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 56 of file inl2weight.cc.

References c_product_avlen, Xapian::Weight::get_average_length(), Xapian::Weight::get_collection_size(), Xapian::Weight::get_doclength_lower_bound(), Xapian::Weight::get_termfreq(), Xapian::Weight::get_wdf_upper_bound(), Xapian::Weight::get_wqf(), log2(), param_c, upper_bound, and wqf_product_idf.

◆ name()

string Xapian::InL2Weight::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 91 of file inl2weight.cc.

Referenced by DEFINE_TESTCASE().

◆ serialise()

string Xapian::InL2Weight::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 97 of file inl2weight.cc.

References param_c, and serialise_double().

Referenced by DEFINE_TESTCASE().

◆ unserialise()

InL2Weight * Xapian::InL2Weight::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
serialisedA string containing the serialised parameters.

Reimplemented from Xapian::Weight.

Definition at line 103 of file inl2weight.cc.

References InL2Weight(), rare, and unserialise_double().

Referenced by DEFINE_TESTCASE().

Member Data Documentation

◆ c_product_avlen

double Xapian::InL2Weight::c_product_avlen
private

Definition at line 847 of file weight.h.

Referenced by get_sumpart(), and init().

◆ param_c

double Xapian::InL2Weight::param_c
private

The wdf normalization parameter in the formula.

Definition at line 840 of file weight.h.

Referenced by clone(), init(), InL2Weight(), and serialise().

◆ upper_bound

double Xapian::InL2Weight::upper_bound
private

The upper bound on the weight a term can give to a document.

Definition at line 843 of file weight.h.

Referenced by get_maxpart(), and init().

◆ wqf_product_idf

double Xapian::InL2Weight::wqf_product_idf
private

The constant values which are used on every call to get_sumpart().

Definition at line 846 of file weight.h.

Referenced by get_sumpart(), and init().


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