xapiancore
1.4.26

Abstract base class for weighting schemes. More...
#include <weight.h>
Public Types  
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...  
Public Member Functions  
Weight ()  
Default constructor, needed by subclass constructors.  
virtual  ~Weight () 
Virtual destructor, because we have virtual methods.  
virtual Weight *  clone () const =0 
Clone this object.  
virtual std::string  name () const 
Return the name of this weighting scheme.  
virtual std::string  serialise () const 
Return this object's parameters serialised as a single string.  
virtual Weight *  unserialise (const std::string &serialised) const 
Unserialise parameters.  
virtual double  get_sumpart (Xapian::termcount wdf, Xapian::termcount doclen, Xapian::termcount uniqterms) const =0 
Calculate the weight contribution for this object's term to a document.  
virtual double  get_maxpart () const =0 
Return an upper bound on what get_sumpart() can return for any document.  
virtual double  get_sumextra (Xapian::termcount doclen, Xapian::termcount uniqterms) const =0 
Calculate the termindependent weight component for a document.  
virtual double  get_maxextra () const =0 
Return an upper bound on what get_sumextra() can return for any document.  
Protected Types  
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  
void  need_stat (stat_flags flag) 
Tell Xapian that your subclass will want a particular statistic.  
virtual void  init (double factor)=0 
Allow the subclass to perform any initialisation it needs to.  
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 withinqueryfrequency 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.  
Abstract base class for weighting schemes.

protected 
Stats which the weighting scheme can use (see need_stat()).
Enumerator  

COLLECTION_SIZE  Number of documents in the collection. 
RSET_SIZE  Number of documents in the RSet. 
AVERAGE_LENGTH  Average length of documents in the collection. 
TERMFREQ  How many documents the current term is in. 
RELTERMFREQ  How many documents in the RSet the current term is in. 
QUERY_LENGTH  Sum of wqf for terms in the query. 
WQF  Withinqueryfrequency of the current term. 
WDF  Withindocumentfrequency of the current term in the current document. 
DOC_LENGTH  Length of the current document (sum wdf). 
DOC_LENGTH_MIN  Lower bound on (nonzero) document lengths. This bound is for the current shard and is suitable for using to calculate upper bounds to return from get_maxpart() and get_maxextra(). 
DOC_LENGTH_MAX  Upper bound on document lengths. This bound is for the current shard and is suitable for using to calculate upper bounds to return from get_maxpart() and get_maxextra(). 
WDF_MAX  Upper bound on wdf. This bound is for the current shard and is suitable for using to calculate upper bounds to return from get_maxpart() and get_maxextra(). 
COLLECTION_FREQ  Sum of wdf over the whole collection for the current term. 
UNIQUE_TERMS  Number of unique terms in the current document. 
TOTAL_LENGTH  Sum of lengths of all documents in the collection. This gives the total number of term occurrences. 
Type of smoothing to use with the Language Model Weighting scheme.
Default is TWO_STAGE_SMOOTHING.

protected 
Don't allow copying.
This would ideally be private, but that causes a compilation error with GCC 4.1 (which appears to be a bug).

pure virtual 
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
Implemented in Xapian::CoordWeight.

inlineprotected 
A lower bound on the minimum length of any document in the shard.
This bound does not include any zerolength documents.
This should only be used by get_maxpart() and get_maxextra().

inlineprotected 
An upper bound on the maximum length of any document in the shard.
This should only be used by get_maxpart() and get_maxextra().

pure 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.
Implemented in Xapian::BoolWeight, Xapian::TfIdfWeight, Xapian::BM25Weight, Xapian::BM25PlusWeight, Xapian::TradWeight, Xapian::InL2Weight, Xapian::IfB2Weight, Xapian::IneB2Weight, Xapian::BB2Weight, Xapian::DLHWeight, Xapian::PL2Weight, Xapian::PL2PlusWeight, Xapian::DPHWeight, Xapian::LMWeight, and Xapian::CoordWeight.

pure 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.
Implemented in Xapian::BoolWeight, Xapian::TfIdfWeight, Xapian::BM25Weight, Xapian::BM25PlusWeight, Xapian::TradWeight, Xapian::InL2Weight, Xapian::IfB2Weight, Xapian::IneB2Weight, Xapian::BB2Weight, Xapian::DLHWeight, Xapian::PL2Weight, Xapian::PL2PlusWeight, Xapian::DPHWeight, Xapian::LMWeight, and Xapian::CoordWeight.

pure virtual 
Calculate the termindependent 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). 
uniqterms  The number of unique terms in the document. 
Implemented in Xapian::BoolWeight, Xapian::TfIdfWeight, Xapian::BM25Weight, Xapian::BM25PlusWeight, Xapian::TradWeight, Xapian::InL2Weight, Xapian::IfB2Weight, Xapian::IneB2Weight, Xapian::BB2Weight, Xapian::DLHWeight, Xapian::PL2Weight, Xapian::PL2PlusWeight, Xapian::DPHWeight, Xapian::LMWeight, and Xapian::CoordWeight.

pure 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). 
uniqterms  Number of unique terms in the document (used for absolute smoothing). 
Implemented in Xapian::TfIdfWeight, Xapian::BM25Weight, Xapian::BM25PlusWeight, Xapian::IfB2Weight, Xapian::LMWeight, Xapian::CoordWeight, Xapian::BoolWeight, Xapian::InL2Weight, Xapian::IneB2Weight, Xapian::BB2Weight, Xapian::DLHWeight, Xapian::PL2Weight, Xapian::PL2PlusWeight, Xapian::DPHWeight, and Xapian::TradWeight.

inlineprotected 
An upper bound on the wdf of this term in the shard.
This should only be used by get_maxpart() and get_maxextra().

protectedpure virtual 
Allow the subclass to perform any initialisation it needs to.
factor  Any scaling factor (e.g. from OP_SCALE_WEIGHT). If the Weight object is for the termindependent 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). 
Implemented in Xapian::CoordWeight.

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 namespacequalified 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 in Xapian::BoolWeight, Xapian::TfIdfWeight, Xapian::BM25Weight, Xapian::BM25PlusWeight, Xapian::TradWeight, Xapian::InL2Weight, Xapian::IfB2Weight, Xapian::IneB2Weight, Xapian::BB2Weight, Xapian::DLHWeight, Xapian::PL2Weight, Xapian::PL2PlusWeight, Xapian::DPHWeight, Xapian::LMWeight, and Xapian::CoordWeight.

inlineprotected 
Tell Xapian that your subclass will want a particular statistic.
Some of the statistics can be costly to fetch or calculate, so Xapian needs to know which are actually going to be used. You should call need_stat() from your constructor for each such statistic.
flag  The stat_flags value for a required statistic. 

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 in Xapian::BoolWeight, Xapian::TfIdfWeight, Xapian::BM25Weight, Xapian::BM25PlusWeight, Xapian::TradWeight, Xapian::InL2Weight, Xapian::IfB2Weight, Xapian::IneB2Weight, Xapian::BB2Weight, Xapian::DLHWeight, Xapian::PL2Weight, Xapian::PL2PlusWeight, Xapian::DPHWeight, Xapian::LMWeight, and Xapian::CoordWeight.

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
serialised  A string containing the serialised parameters. 
Reimplemented in Xapian::BoolWeight, Xapian::TfIdfWeight, Xapian::BM25Weight, Xapian::BM25PlusWeight, Xapian::TradWeight, Xapian::InL2Weight, Xapian::IfB2Weight, Xapian::IneB2Weight, Xapian::BB2Weight, Xapian::DLHWeight, Xapian::PL2Weight, Xapian::PL2PlusWeight, Xapian::DPHWeight, Xapian::LMWeight, and Xapian::CoordWeight.