#include <weight.h>
Inheritance diagram for Xapian::TradWeight:
Public Member Functions | |
TradWeight (double k=1.0) | |
std::string | name () const |
std::string | serialise () const |
TradWeight * | unserialise (const std::string &s) const |
Xapian::weight | get_sumpart (Xapian::termcount wdf, Xapian::termcount doclen) const |
Xapian::weight | get_maxpart () const |
Xapian::weight | get_sumextra (Xapian::termcount doclen) const |
Xapian::weight | get_maxextra () const |
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), except that the latter returns weights (k+1) times larger.
Xapian::TradWeight::TradWeight | ( | double | k = 1.0 |
) | [inline, explicit] |
Construct a TradWeight.
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 k1 is, the more they do. (default 1) |
std::string Xapian::TradWeight::name | ( | ) | const [virtual] |
Return the name of this weighting scheme.
This name is used by the remote backend. It is passed 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 in your weighting scheme, you can just implement this to throw Xapian::UnimplementedError.
Implements Xapian::Weight.
std::string Xapian::TradWeight::serialise | ( | ) | const [virtual] |
Return this object's parameters serialised as a single string.
If you don't want to support the remote backend in your weighting scheme, you can just implement this to throw Xapian::UnimplementedError.
Implements Xapian::Weight.
TradWeight* Xapian::TradWeight::unserialise | ( | const std::string & | s | ) | 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 in your weighting scheme, you can just implement this to throw Xapian::UnimplementedError.
Note that the returned object will be deallocated by Xapian after use with "delete". It must therefore have been allocated with "new".
Implements Xapian::Weight.
Xapian::weight Xapian::TradWeight::get_sumpart | ( | Xapian::termcount | wdf, | |
Xapian::termcount | doclen | |||
) | 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:
wdf | The within document frequency of the term in the document. | |
doclen | The document's length (unnormalised). |
Implements Xapian::Weight.
Xapian::weight Xapian::TradWeight::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.
Xapian::weight Xapian::TradWeight::get_sumextra | ( | Xapian::termcount | doclen | ) | 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:
doclen | The document's length (unnormalised). |
Implements Xapian::Weight.
Xapian::weight Xapian::TradWeight::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.