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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
***********************************************************************/
#pragma once
#include <string>
#include <vector>
#include "Factor.h"
#include "TypeDef.h"
#include "Util.h"
#include "ScoreProducer.h"
#include "Word.h"
class FactorCollection;
class Factor;
class Phrase;
//! Abstract base class which represent a language model on a contiguous phrase
class LanguageModel : public ScoreProducer
{
protected:
float m_weight; //! scoring weight. Shouldn't this now be superceded by ScoreProducer???
std::string m_filePath; //! for debugging purposes
size_t m_nGramOrder; //! max n-gram length contained in this LM
Word m_sentenceStartArray, m_sentenceEndArray; //! Contains factors which represents the beging and end words for this LM.
//! Usually <s> and </s>
/** constructor to be called by inherited class
* \param registerScore whether this LM will be directly used to score sentence.
* Usually true, except where LM is a component in a composite LM, eg. LanguageModelJoint
*/
LanguageModel(bool registerScore, ScoreIndexManager &scoreIndexManager);
public:
/* Returned from LM implementations which points at the state used. For example, if a trigram score was requested
* but the LM backed off to using the trigram, the State pointer will point to the bigram.
* Used for more agressive pruning of hypothesis
*/
typedef const void* State;
virtual ~LanguageModel();
//! see ScoreProducer.h
size_t GetNumScoreComponents() const;
//! Single or multi-factor
virtual LMType GetLMType() 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
*/
void CalcScore(const Phrase &phrase
, float &fullScore
, float &ngramScore) const;
/* get score of n-gram. n-gram should not be bigger than m_nGramOrder
* Specific implementation can return State and len data to be used in hypothesis pruning
* \param contextFactor n-gram to be scored
* \param finalState state used by LM. Return arg
* \param len ???
*/
virtual float GetValue(const std::vector<const Word*> &contextFactor
, State* finalState = 0
, unsigned int* len = 0) const = 0;
//! get State for a particular n-gram
State GetState(const std::vector<const Word*> &contextFactor, unsigned int* len = 0) const;
//! max n-gram order of LM
size_t GetNGramOrder() const
{
return m_nGramOrder;
}
//! Contains factors which represents the beging and end words for this LM. Usually <s> and </s>
const Word &GetSentenceStartArray() const
{
return m_sentenceStartArray;
}
const Word &GetSentenceEndArray() const
{
return m_sentenceEndArray;
}
//! scoring weight. Shouldn't this now be superceded by ScoreProducer???
float GetWeight() const
{
return m_weight;
}
void SetWeight(float weight)
{
m_weight = weight;
}
virtual std::string GetScoreProducerDescription() const = 0;
//! overrideable funtions for IRST LM to cleanup. Maybe something to do with on demand/cache loading/unloading
virtual void InitializeBeforeSentenceProcessing(){};
virtual void CleanUpAfterSentenceProcessing() {};
};
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