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/***********************************************************************
Moses - statistical machine translation system
Copyright (C) 2006-2014 University of Edinburgh
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
This library 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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
***********************************************************************/
#pragma once
#include <cassert>
#include "ChartHypothesis.h"
#include "ScoreComponentCollection.h"
#include "FF/InternalTree.h"
#include <boost/unordered_set.hpp>
#include <boost/weak_ptr.hpp>
#include <boost/shared_ptr.hpp>
#include <queue>
#include <vector>
namespace Moses
{
// k-best list extractor that implements algorithm 3 from this paper:
//
// Liang Huang and David Chiang
// "Better k-best parsing"
// In Proceedings of IWPT 2005
//
class ChartKBestExtractor
{
public:
struct Vertex;
struct UnweightedHyperarc {
boost::shared_ptr<Vertex> head;
std::vector<boost::shared_ptr<Vertex> > tail;
};
struct Derivation {
Derivation(const UnweightedHyperarc &);
Derivation(const Derivation &, std::size_t);
UnweightedHyperarc edge;
std::vector<std::size_t> backPointers;
std::vector<boost::shared_ptr<Derivation> > subderivations;
float score;
};
struct DerivationOrderer {
bool operator()(const boost::weak_ptr<Derivation> &d1,
const boost::weak_ptr<Derivation> &d2) const {
boost::shared_ptr<Derivation> s1(d1);
boost::shared_ptr<Derivation> s2(d2);
return s1->score < s2->score;
}
};
struct Vertex {
typedef std::priority_queue<boost::weak_ptr<Derivation>,
std::vector<boost::weak_ptr<Derivation> >,
DerivationOrderer> DerivationQueue;
Vertex(const ChartHypothesis &h) : hypothesis(h), visited(false) {}
const ChartHypothesis &hypothesis;
std::vector<boost::weak_ptr<Derivation> > kBestList;
DerivationQueue candidates;
bool visited;
};
typedef std::vector<boost::shared_ptr<Derivation> > KBestVec;
// Extract the k-best list from the search hypergraph given the full, sorted
// list of top-level vertices.
void Extract(const std::vector<const ChartHypothesis*> &topHypos,
std::size_t k, KBestVec &);
static Phrase GetOutputPhrase(const Derivation &);
static boost::shared_ptr<ScoreComponentCollection> GetOutputScoreBreakdown(const Derivation &);
static TreePointer GetOutputTree(const Derivation &);
private:
typedef boost::unordered_map<const ChartHypothesis *,
boost::shared_ptr<Vertex> > VertexMap;
struct DerivationHasher {
std::size_t operator()(const boost::shared_ptr<Derivation> &d) const {
std::size_t seed = 0;
boost::hash_combine(seed, d->edge.head);
boost::hash_combine(seed, d->edge.tail);
boost::hash_combine(seed, d->backPointers);
return seed;
}
};
struct DerivationEqualityPred {
bool operator()(const boost::shared_ptr<Derivation> &d1,
const boost::shared_ptr<Derivation> &d2) const {
return d1->edge.head == d2->edge.head &&
d1->edge.tail == d2->edge.tail &&
d1->backPointers == d2->backPointers;
}
};
typedef boost::unordered_set<boost::shared_ptr<Derivation>, DerivationHasher,
DerivationEqualityPred> DerivationSet;
UnweightedHyperarc CreateEdge(const ChartHypothesis &);
boost::shared_ptr<Vertex> FindOrCreateVertex(const ChartHypothesis &);
void GetCandidates(Vertex &, std::size_t);
void LazyKthBest(Vertex &, std::size_t, std::size_t);
void LazyNext(Vertex &, const Derivation &, std::size_t);
VertexMap m_vertexMap;
DerivationSet m_derivations;
};
} // namespace Moses
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