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// $Id$
/***********************************************************************
Moses - factored phrase-based language decoder
Copyright (C) 2006 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
***********************************************************************/
#ifndef moses_LanguageModel_h
#define moses_LanguageModel_h
#include <string>
#include <cstddef>
#include "../FeatureFunction.h"
namespace Moses
{
class FactorCollection;
class Factor;
class Phrase;
//! Abstract base class which represent a language model on a contiguous phrase
class LanguageModel : public StatefulFeatureFunction {
protected:
LanguageModel();
// This can't be in the constructor for virual function dispatch reasons
bool m_enableOOVFeature;
public:
virtual ~LanguageModel();
// Make another feature without copying the underlying model data.
virtual LanguageModel *Duplicate() const = 0;
bool OOVFeatureEnabled() const {
return m_enableOOVFeature;
}
float GetWeight() const;
float GetOOVWeight() const;
std::string GetScoreProducerWeightShortName(unsigned) const {
return "lm";
}
virtual void InitializeBeforeSentenceProcessing() {}
virtual void CleanUpAfterSentenceProcessing() {}
virtual const FFState* EmptyHypothesisState(const InputType &input) const = 0;
/* whether this LM can be used on a particular phrase.
* Should return false if phrase size = 0 or factor types required don't exists
*/
virtual bool Useable(const Phrase &phrase) const = 0;
/* calc total unweighted LM score of this phrase and return score via arguments.
* Return scores should always be in natural log, regardless of representation with LM implementation.
* Uses GetValue() of inherited class.
* Useable() should be called beforehand on the phrase
* \param fullScore scores of all unigram, bigram... of contiguous n-gram of the phrase
* \param ngramScore score of only n-gram of order m_nGramOrder
* \param oovCount number of LM OOVs
*/
virtual void CalcScore(const Phrase &phrase, float &fullScore, float &ngramScore, std::size_t &oovCount) const = 0;
};
}
#endif
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