#include <enquire.h>
Inheritance diagram for Xapian::TradWeight:
Public Member Functions | |
| TradWeight (double k) | |
| Construct a TradWeight. | |
| TradWeight () | |
| TradWeight * | clone () const |
| Return a new weight object of this type. | |
| ~TradWeight () | |
| std::string | name () const |
| Name of the weighting scheme. | |
| std::string | serialise () const |
| Serialise object parameters into a string. | |
| TradWeight * | unserialise (const std::string &s) const |
| Create object given string serialisation returned by serialise(). | |
| Xapian::weight | get_sumpart (Xapian::termcount wdf, Xapian::doclength len) const |
| Get a weight which is part of the sum over terms being performed. | |
| Xapian::weight | get_maxpart () const |
| Gets the maximum value that get_sumpart() may return. | |
| Xapian::weight | get_sumextra (Xapian::doclength len) const |
| Get an extra weight for a document to add to the sum calculated over the query terms. | |
| Xapian::weight | get_maxextra () const |
| Gets the maximum value that get_sumextra() may return. | |
| bool | get_sumpart_needs_doclength () const |
| return false if the weight object doesn't need doclength | |
Private Member Functions | |
| void | calc_termweight () const |
Private Attributes | |
| Xapian::weight | termweight |
| Xapian::doclength | lenpart |
| double | param_k |
| bool | weight_calculated |
This class implements the Traditional Probabilistic Weighting scheme, as described by the early papers on Probabilistic Retrieval. BM25 generally gives better results.
The Traditional weighting scheme formula is
![\[ \sum_{t}\frac{f_{t,d}}{k.L_{d}+f_{t,d}}.w_{t} \]](form_10.png)
where
is the termweight of term t
is the within document frequency of term t in document d
is the normalised length of document d
is a user specifiable parameterTradWeight(k) is equivalent to BM25Weight(k, 0, 0, 1, 0), except that the latter returns weights (k+1) times larger.
Definition at line 1252 of file enquire.h.
| Xapian::TradWeight::TradWeight | ( | double | k | ) | [inline, explicit] |
Construct a TradWeight.
| k | parameter governing the importance of within document frequency and document length - any non-negative number (0 meaning to ignore wdf and doc length when calculating weights). Default is 1. |
| Xapian::TradWeight::TradWeight | ( | ) | [inline] |
| void Xapian::TradWeight::calc_termweight | ( | ) | const [private] |
Definition at line 59 of file tradweight.cc.
References Assert, Xapian::Weight::Internal::collection_size, DEBUGCALL, DEBUGLINE, Xapian::Weight::internal, lenpart, param_k, Xapian::Weight::Internal::rset_size, termweight, and weight_calculated.
Referenced by get_maxpart(), get_sumpart(), and get_sumpart_needs_doclength().
| TradWeight * Xapian::TradWeight::clone | ( | ) | const [virtual] |
Return a new weight object of this type.
A subclass called FooWeight taking parameters param1 and param2 should implement this as:
virtual FooWeight * clone() const { return new FooWeight(param1, param2); }
Implements Xapian::Weight.
Definition at line 39 of file tradweight.cc.
References param_k, and TradWeight().
| string Xapian::TradWeight::name | ( | ) | const [virtual] |
Name of the weighting scheme.
If the subclass is called FooWeight, this should return "Foo".
Implements Xapian::Weight.
Definition at line 43 of file tradweight.cc.
Referenced by DEFINE_TESTCASE().
| string Xapian::TradWeight::serialise | ( | ) | const [virtual] |
Serialise object parameters into a string.
Implements Xapian::Weight.
Definition at line 45 of file tradweight.cc.
References param_k, and serialise_double().
Referenced by DEFINE_TESTCASE().
| TradWeight* Xapian::TradWeight::unserialise | ( | const std::string & | s | ) | const [virtual] |
| Xapian::weight Xapian::TradWeight::get_sumpart | ( | Xapian::termcount | wdf, | |
| Xapian::doclength | len | |||
| ) | const [virtual] |
Get a weight which is part of the sum over terms being performed.
This returns a weight for a given term and document. These weights are summed to give a total weight for the document.
| wdf | the within document frequency of the term. | |
| len | the (unnormalised) document length. |
Implements Xapian::Weight.
Definition at line 111 of file tradweight.cc.
References calc_termweight(), DEBUGCALL, lenpart, RETURN, termweight, and weight_calculated.
| Xapian::weight Xapian::TradWeight::get_maxpart | ( | ) | const [virtual] |
Gets the maximum value that get_sumpart() may return.
This is used in optimising searches, by having the postlist tree decay appropriately when parts of it can have limited, or no, further effect.
Implements Xapian::Weight.
Definition at line 124 of file tradweight.cc.
References calc_termweight(), DEBUGCALL, RETURN, termweight, and weight_calculated.
| Xapian::weight Xapian::TradWeight::get_sumextra | ( | Xapian::doclength | len | ) | const [virtual] |
Get an extra weight for a document to add to the sum calculated over the query terms.
This returns a weight for a given document, and is used by some weighting schemes to account for influence such as document length.
| len | the (unnormalised) document length. |
Implements Xapian::Weight.
Definition at line 133 of file tradweight.cc.
| Xapian::weight Xapian::TradWeight::get_maxextra | ( | ) | const [virtual] |
Gets the maximum value that get_sumextra() may return.
This is used in optimising searches.
Implements Xapian::Weight.
Definition at line 140 of file tradweight.cc.
| bool Xapian::TradWeight::get_sumpart_needs_doclength | ( | ) | const [virtual] |
return false if the weight object doesn't need doclength
Reimplemented from Xapian::Weight.
Definition at line 146 of file tradweight.cc.
References calc_termweight(), lenpart, and weight_calculated.
Xapian::weight Xapian::TradWeight::termweight [mutable, private] |
Definition at line 1254 of file enquire.h.
Referenced by calc_termweight(), get_maxpart(), and get_sumpart().
Xapian::doclength Xapian::TradWeight::lenpart [mutable, private] |
Definition at line 1255 of file enquire.h.
Referenced by calc_termweight(), get_sumpart(), and get_sumpart_needs_doclength().
double Xapian::TradWeight::param_k [private] |
Definition at line 1257 of file enquire.h.
Referenced by calc_termweight(), clone(), and serialise().
bool Xapian::TradWeight::weight_calculated [mutable, private] |
Definition at line 1259 of file enquire.h.
Referenced by calc_termweight(), get_maxpart(), get_sumpart(), and get_sumpart_needs_doclength().