Xapian::TradWeight Class Reference

Xapian::Weight subclass implementing the traditional probabilistic formula. More...

#include <weight.h>

Inheritance diagram for Xapian::TradWeight:

Public Member Functions
	TradWeight (double k=1.0)
	Construct a TradWeight.
Public Member Functions inherited from Xapian::BM25Weight
	BM25Weight (double k1, double k2, double k3, double b, double min_normlen)
	Construct a BM25Weight.
std::string	name () const
	Return the name of this weighting scheme, e.g.
std::string	serialise () const
	Return this object's parameters serialised as a single string.
BM25Weight *	unserialise (const std::string &serialised) const
	Unserialise parameters.
double	get_sumpart (Xapian::termcount wdf, Xapian::termcount doclen, Xapian::termcount uniqterm, Xapian::termcount wdfdocmax) const
	Calculate the weight contribution for this object's term to a document.
double	get_maxpart () const
	Return an upper bound on what get_sumpart() can return for any document.
double	get_sumextra (Xapian::termcount doclen, Xapian::termcount uniqterms, Xapian::termcount wdfdocmax) const
	Calculate the term-independent weight component for a document.
double	get_maxextra () const
	Return an upper bound on what get_sumextra() can return for any document.
BM25Weight *	create_from_parameters (const char *params) const
	Create from a human-readable parameter string.
Public Member Functions inherited from Xapian::Weight
	Weight ()
	Default constructor, needed by subclass constructors.
virtual	~Weight ()
	Virtual destructor, because we have virtual methods.

Additional Inherited Members
Static Public Member Functions inherited from Xapian::Weight
static const Weight *	create (const std::string &scheme, const Registry &reg=Registry())
	Return the appropriate weighting scheme object.
Protected Types inherited from Xapian::Weight
enum	stat_flags {   COLLECTION_SIZE = 0 , RSET_SIZE = 0 , AVERAGE_LENGTH = 4 , TERMFREQ = 1 ,   RELTERMFREQ = 1 , QUERY_LENGTH = 0 , WQF = 0 , WDF = 2 ,   DOC_LENGTH = 8 , DOC_LENGTH_MIN = 16 , DOC_LENGTH_MAX = 32 , WDF_MAX = 64 ,   COLLECTION_FREQ = 1 , UNIQUE_TERMS = 128 , TOTAL_LENGTH = 256 , WDF_DOC_MAX = 512 ,   UNIQUE_TERMS_MIN = 1024 , UNIQUE_TERMS_MAX = 2048 , DB_DOC_LENGTH_MIN = 4096 , DB_DOC_LENGTH_MAX = 8192 ,   DB_UNIQUE_TERMS_MIN = 16384 , DB_UNIQUE_TERMS_MAX = 32768 , DB_WDF_MAX = 65536 , IS_BOOLWEIGHT_ = static_cast<int>(0x80000000) }
	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.
	Weight (const Weight &)
	Don't allow copying.
Xapian::doccount	get_collection_size () const
	The number of documents in the collection.
Xapian::doccount	get_rset_size () const
	The number of documents marked as relevant.
Xapian::doclength	get_average_length () const
	The average length of a document in the collection.
Xapian::doccount	get_termfreq () const
	The number of documents which this term indexes.
Xapian::doccount	get_reltermfreq () const
	The number of relevant documents which this term indexes.
Xapian::termcount	get_collection_freq () const
	The collection frequency of the term.
Xapian::termcount	get_query_length () const
	The length of the query.
Xapian::termcount	get_wqf () const
	The within-query-frequency of this term.
Xapian::termcount	get_doclength_upper_bound () const
	An upper bound on the maximum length of any document in the shard.
Xapian::termcount	get_doclength_lower_bound () const
	A lower bound on the minimum length of any document in the shard.
Xapian::termcount	get_wdf_upper_bound () const
	An upper bound on the wdf of this term in the shard.
Xapian::totallength	get_total_length () const
	Total length of all documents in the collection.
Xapian::termcount	get_unique_terms_upper_bound () const
	A lower bound on the number of unique terms in any document in the shard.
Xapian::termcount	get_unique_terms_lower_bound () const
	An upper bound on the number of unique terms in any document in the shard.
Xapian::termcount	get_db_doclength_upper_bound () const
	An upper bound on the maximum length of any document in the database.
Xapian::termcount	get_db_doclength_lower_bound () const
	A lower bound on the minimum length of any document in the database.
Xapian::termcount	get_db_unique_terms_upper_bound () const
	A lower bound on the number of unique terms in any document in the database.
Xapian::termcount	get_db_unique_terms_lower_bound () const
	An upper bound on the number of unique terms in any document in the database.
Xapian::termcount	get_db_wdf_upper_bound () const
	An upper bound on the wdf of this term in the database.

Detailed Description

Xapian::Weight subclass implementing the traditional probabilistic formula.

This class implements the "traditional" Probabilistic Weighting scheme, as described by the early papers on Probabilistic Retrieval. BM25 generally gives better results.

TradWeight(k) is equivalent to BM25Weight(k, 0, 0, 1, 0), and since Xapian 2.0.0 TradWeight is actually implemented as a subclass of BM25Weight. In earlier versions is was a separate class which was equivalent except it returned weights (k+1) times smaller.

Deprecated

Use BM25Weight(k, 0, 0, 1, 0) instead.

Constructor & Destructor Documentation

TradWeight()

Xapian::TradWeight::TradWeight ( double k = 1.0 )

inlineexplicit

Construct a TradWeight.

Parameters

k	A non-negative parameter controlling how influential within-document-frequency (wdf) and document length are. k=0 means that wdf and document length don't affect the weights. The larger k is, the more they do. (default 1)

References Xapian::BM25Weight::BM25Weight().

---

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

• xapian/weight.h