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/** @file synonympostlist.h
* @brief Combine subqueries, weighting as if they are synonyms
*/
/* Copyright 2007,2009 Lemur Consulting Ltd
* Copyright 2009,2011,2014 Olly Betts
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
#ifndef XAPIAN_INCLUDED_SYNONYMPOSTLIST_H
#define XAPIAN_INCLUDED_SYNONYMPOSTLIST_H
#include "multimatch.h"
#include "api/postlist.h"
/** A postlist comprising several postlists SYNONYMed together.
*
* This postlist returns all postings in the OR of the sub postlists, but
* returns weights as if they represented a single term. The term frequency
* portion of the weight is approximated.
*/
class SynonymPostList : public PostList {
/** The subtree, which starts as an OR of all the sub-postlists being
* joined with Synonym, but may decay into something else.
*/
PostList * subtree;
/** The object which is using this postlist to perform a match.
*
* This object needs to be notified when the tree changes such that the
* maximum weights need to be recalculated.
*/
MultiMatch * matcher;
/// Weighting object used for calculating the synonym weights.
const Xapian::Weight * wt;
/// Flag indicating whether the weighting object needs the doclength.
bool want_doclength;
/// Flag indicating whether the weighting object needs the wdf.
bool want_wdf;
/** Flag indicating whether the weighting object needs the number of unique
* terms.
*/
bool want_unique_terms;
/// Flag indicating if we've called recalc_maxweight on the subtree yet.
bool have_calculated_subtree_maxweights;
/// Lower bound on doclength in the subdatabase we're working over.
Xapian::termcount doclen_lower_bound;
public:
SynonymPostList(PostList * subtree_, MultiMatch * matcher_,
Xapian::termcount doclen_lower_bound_)
: subtree(subtree_), matcher(matcher_), wt(NULL),
want_doclength(false), want_wdf(false), want_unique_terms(false),
have_calculated_subtree_maxweights(false),
doclen_lower_bound(doclen_lower_bound_) { }
~SynonymPostList();
/** Set the weight object to be used for the synonym postlist.
*
* Ownership of the weight object passes to the synonym postlist - the
* caller must not delete it after use.
*/
void set_weight(const Xapian::Weight * wt_);
PostList *next(double w_min);
PostList *skip_to(Xapian::docid did, double w_min);
double get_weight() const;
double get_maxweight() const;
double recalc_maxweight();
// The following methods just call through to the subtree.
Xapian::termcount get_wdf() const;
Xapian::doccount get_termfreq_min() const;
Xapian::doccount get_termfreq_est() const;
Xapian::doccount get_termfreq_max() const;
// Note - we don't need to implement get_termfreq_est_using_stats()
// because a synonym when used as a child of a synonym will be optimised
// to an OR.
Xapian::docid get_docid() const;
Xapian::termcount get_doclength() const;
Xapian::termcount get_unique_terms() const;
bool at_end() const;
Xapian::termcount count_matching_subqs() const;
std::string get_description() const;
};
#endif /* XAPIAN_INCLUDED_SYNONYMPOSTLIST_H */
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