Main Page   Class Hierarchy   Alphabetical List   Compound List   File List   Compound Members   File Members  

OmEnquire Class Reference

This class provides an interface to the information retrieval system for the purpose of searching. More...

#include <omenquire.h>

List of all members.

Public Methods

 OmEnquire (const OmDatabase &databases, OmErrorHandler *errorhandler_=0)
 Create an OmEnquire object. More...

 ~OmEnquire ()
 Close the OmEnquire object. More...

void set_query (const OmQuery &query_)
 Set the query to run. More...

const OmQueryget_query ()
 Get the query which has been set. More...

void set_weighting_scheme (const OmWeight &weight_)
 Set the weighting scheme to use for queries. More...

void set_collapse_key (om_valueno collapse_key)
 Set the collapse key to use for queries. More...

void set_sort_forward (bool sort_forward)
 Set the collapse key to use for queries. More...

void set_cutoff (int percent_cutoff, om_weight weight_cutoff=0)
 Set the percentage and/or weight cutoffs. More...

void set_sorting (om_valueno sort_key, int sort_bands)
 Set the percentage and/or weight cutoffs. More...

void set_bias (om_weight bias_weight, time_t bias_halflife)
 Set the bias functor parameters. More...

OmMSet get_mset (om_doccount first, om_doccount maxitems, const OmRSet *omrset=0, const OmMatchDecider *mdecider=0) const
 Get (a portion of) the match set for the current query. More...

OmESet get_eset (om_termcount maxitems, const OmRSet &omrset, int flags=0, double k=1.0, const OmExpandDecider *edecider=0) const
 Get the expand set for the given rset. More...

OmESet get_eset (om_termcount maxitems, const OmRSet &omrset, const OmExpandDecider *edecider) const
 Get the expand set for the given rset. More...

OmTermIterator get_matching_terms_begin (om_docid did) const
 Get terms which match a given document, by document id. More...

OmTermIterator get_matching_terms_end (om_docid did) const
 End iterator corresponding to get_matching_terms_begin(). More...

OmTermIterator get_matching_terms_begin (const OmMSetIterator &it) const
 Get terms which match a given document, by match set item. More...

OmTermIterator get_matching_terms_end (const OmMSetIterator &it) const
 End iterator corresponding to get_matching_terms_begin(). More...

void register_match_decider (const std::string &name, const OmMatchDecider *mdecider=NULL)
 Register an OmMatchDecider. More...

std::string get_description () const
 Introspection method. More...


Public Attributes

Internal * internal

Static Public Attributes

const int include_query_terms = 1
const int use_exact_termfreq = 2


Detailed Description

This class provides an interface to the information retrieval system for the purpose of searching.

Databases are usually opened lazily, so exceptions may not be thrown where you would expect them to be. You should catch OmError exceptions when calling any method in OmEnquire.

Exceptions:
OmInvalidArgumentError  will be thrown if an invalid argument is supplied, for example, an unknown database type.
OmOpeningError  will be thrown if the database cannot be opened (for example, a required file cannot be found).


Constructor & Destructor Documentation

OmEnquire::OmEnquire const OmDatabase   databases,
OmErrorHandler   errorhandler_ = 0
 

Create an OmEnquire object.

This specification cannot be changed once the OmEnquire is opened: you must create a new OmEnquire object to access a different database, or set of databases.

Parameters:
database  Specification of the database or databases to use.
errorhandler_  A pointer to the error handler to use. Ownership of the object pointed to is not assumed by the OmEnquire object - the user should delete the OmErrorHandler object after the OmEnquire object is deleted. To use no error handler, this parameter should be 0.

OmEnquire::~OmEnquire  
 

Close the OmEnquire object.

This frees all resources associated with the OmEnquire object, such as handles on the databases used. As a result, any object which refers to these databases, such as an OmDocument, will become invalid after the destruction of the object, and must not be used subsequently. (FIXME: I don't think this is actually true - check)


Member Function Documentation

std::string OmEnquire::get_description   const
 

Introspection method.

Returns:
A string representing the enquire object.

OmESet OmEnquire::get_eset om_termcount    maxitems,
const OmRSet   omrset,
const OmExpandDecider   edecider
const [inline]
 

Get the expand set for the given rset.

Parameters:
maxitems  the maximum number of items to return.
omrset  the relevance set to use when performing the expand operation.
edecider  a decision functor to use to decide whether a given term should be put in the ESet
Returns:
An OmESet object containing the results of the expand.
Exceptions:
OmInvalidArgumentError  See class documentation.
OmOpeningError  See class documentation.

OmESet OmEnquire::get_eset om_termcount    maxitems,
const OmRSet   omrset,
int    flags = 0,
double    k = 1.0,
const OmExpandDecider   edecider = 0
const
 

Get the expand set for the given rset.

Parameters:
maxitems  the maximum number of items to return.
omrset  the relevance set to use when performing the expand operation.
flags  zero or more of these values |-ed together:
  • OmEnquire::include_query_terms query terms may be returned from expand
  • OmEnquire::use_exact_termfreq for multi dbs, calculate the exact termfreq; otherwise an approximation is used which can greatly improve efficiency, but still returns good results.
Parameters:
k  the parameter k in the query expansion algorithm (default is 1.0)
edecider  a decision functor to use to decide whether a given term should be put in the ESet
Returns:
An OmESet object containing the results of the expand.
Exceptions:
OmInvalidArgumentError  See class documentation.
OmOpeningError  See class documentation.

OmTermIterator OmEnquire::get_matching_terms_begin const OmMSetIterator   it const
 

Get terms which match a given document, by match set item.

This method returns the terms in the current query which match the given document.

If the underlying database has suitable support, using this call (rather than passing an om_docid) will enable the system to ensure that the correct data is returned, and that the document has not been deleted or changed since the query was performed.

Parameters:
it  The iterator for which to retrieve the matching terms.
Returns:
An iterator returning the terms which match the document. The terms will be returned (as far as this makes any sense) in the same order as the terms in the query. Terms will not occur more than once, even if they do in the query.
Exceptions:
OmInvalidArgumentError  See class documentation.
OmOpeningError  See class documentation.
OmDocNotFoundError  The document specified could not be found in the database.

OmTermIterator OmEnquire::get_matching_terms_begin om_docid    did const
 

Get terms which match a given document, by document id.

This method returns the terms in the current query which match the given document.

It is possible for the document to have been removed from the database between the time it is returned in an mset, and the time that this call is made. If possible, you should specify an OmMSetIterator instead of a om_docid, since this will enable database backends with suitable support to prevent this occurring.

Note that a query does not need to have been run in order to make this call.

Parameters:
did  The document id for which to retrieve the matching terms.
Returns:
An iterator returning the terms which match the document. The terms will be returned (as far as this makes any sense) in the same order as the terms in the query. Terms will not occur more than once, even if they do in the query.
Exceptions:
OmInvalidArgumentError  See class documentation.
OmOpeningError  See class documentation.
OmDocNotFoundError  The document specified could not be found in the database.

OmTermIterator OmEnquire::get_matching_terms_end const OmMSetIterator   it const
 

End iterator corresponding to get_matching_terms_begin().

OmTermIterator OmEnquire::get_matching_terms_end om_docid    did const
 

End iterator corresponding to get_matching_terms_begin().

OmMSet OmEnquire::get_mset om_doccount    first,
om_doccount    maxitems,
const OmRSet   omrset = 0,
const OmMatchDecider   mdecider = 0
const
 

Get (a portion of) the match set for the current query.

Parameters:
first  the first item in the result set to return. A value of zero corresponds to the first item returned being that with the highest score. A value of 10 corresponds to the first 10 items being ignored, and the returned items starting at the eleventh.
maxitems  the maximum number of items to return.
omrset  the relevance set to use when performing the query.
mdecider  a decision functor to use to decide whether a given document should be put in the MSet
Returns:
An OmMSet object containing the results of the query.
Exceptions:
OmInvalidArgumentError  See class documentation.
OmOpeningError  See class documentation.

const OmQuery& OmEnquire::get_query  
 

Get the query which has been set.

This is only valid after set_query() has been called.

Exceptions:
OmInvalidArgumentError  will be thrown if query has not yet been set.

void OmEnquire::register_match_decider const std::string &    name,
const OmMatchDecider   mdecider = NULL
 

Register an OmMatchDecider.

void OmEnquire::set_bias om_weight    bias_weight,
time_t    bias_halflife
 

Set the bias functor parameters.

NB this is a temporary API for this feature.

Parameters:
bias_weight  Maximum weight bias functor can add (and which is given to document with a time now or in the future).
bias_halflife  the match bias decays exponentially as you go back in time. This sets the half-life of this decay in seconds (default 0 => no bias).

void OmEnquire::set_collapse_key om_valueno    collapse_key
 

Set the collapse key to use for queries.

Parameters:
collapse_key  key number to collapse on - duplicates mset entries will be removed based on this key (default is om_valueno(-1) which means no collapsing).

void OmEnquire::set_cutoff int    percent_cutoff,
om_weight    weight_cutoff = 0
 

Set the percentage and/or weight cutoffs.

Parameters:
percent_cutoff  Minimum percentage score for returned documents. If a document has a lower percentage score than this, it will not appear in the mset. If your intention is to return only matches which contain all the terms in the query, then it's more efficient to use OmQuery::OP_AND instead of OmQuery::OP_OR in the query that to set this to 100%). (default 0 => no percentage cut-off).
weight_cutoff  Minimum weight for a document to be returned. If a document has a lower score that this, it will not appear in the mset. It is usually only possible to choose an appropriate weight for cutoff based on the results of a previous run of the same query; this is thus mainly useful for alerting operations. The other potential use is with a user specified weighting scheme.

void OmEnquire::set_query const OmQuery   query_
 

Set the query to run.

Parameters:
query_  the new query to run.
Exceptions:
OmInvalidArgumentError  See class documentation.
OmOpeningError  See class documentation.

void OmEnquire::set_sort_forward bool    sort_forward
 

Set the collapse key to use for queries.

Parameters:
sort_forward  If true, documents with the same weight will be returned in ascending document order; if false, they will be returned in descending order. (default true)

void OmEnquire::set_sorting om_valueno    sort_key,
int    sort_bands
 

Set the percentage and/or weight cutoffs.

Parameters:
sort_key  value number to reorder on. Sorting is with a string compare. Higher is better. If match_sort_key is set, but match_sort_bands isn't, sort the whole mset my the key. (default is om_valueno(-1) which means re-sort by doc id
  • ascending or descending as controlled by sort_forward).
Parameters:
sort_bands  sort results into this many bands of equal percentage relevance. Within each band, sort by the value number specified by sort_key. (default is 0 which means no re-sorting).

void OmEnquire::set_weighting_scheme const OmWeight   weight_
 

Set the weighting scheme to use for queries.

Parameters:
weight_  the new weighting scheme. If no weighting scheme is specified, the default is BM25 with A=1, B=1, C=0, D=0.5, min_normlen=0.5


The documentation for this class was generated from the following file:
Documentation for Xapian (version 0.6.4).
Generated on 10 Apr 2003 by Doxygen 1.2.15.