mirror of
https://github.com/moses-smt/mosesdecoder.git
synced 2024-11-10 10:59:21 +03:00
395 lines
15 KiB
C++
395 lines
15 KiB
C++
#include "Manager.h"
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#include "Timer.h"
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#include "SearchNormal.h"
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#include "SentenceStats.h"
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using namespace std;
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namespace Moses
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{
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/**
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* Organizing main function
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*
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* /param source input sentence
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* /param transOptColl collection of translation options to be used for this sentence
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*/
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SearchNormal::SearchNormal(Manager& manager, const InputType &source, const TranslationOptionCollection &transOptColl)
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:Search(manager)
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,m_source(source)
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,m_hypoStackColl(source.GetSize() + 1)
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,m_start(clock())
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,interrupted_flag(0)
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,m_transOptColl(transOptColl)
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{
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VERBOSE(1, "Translating: " << m_source << endl);
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const StaticData &staticData = StaticData::Instance();
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// only if constraint decoding (having to match a specified output)
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// long sentenceID = source.GetTranslationId();
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// initialize the stacks: create data structure and set limits
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std::vector < HypothesisStackNormal >::iterator iterStack;
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for (size_t ind = 0 ; ind < m_hypoStackColl.size() ; ++ind) {
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HypothesisStackNormal *sourceHypoColl = new HypothesisStackNormal(m_manager);
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sourceHypoColl->SetMaxHypoStackSize(staticData.GetMaxHypoStackSize(),
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staticData.GetMinHypoStackDiversity());
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sourceHypoColl->SetBeamWidth(staticData.GetBeamWidth());
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m_hypoStackColl[ind] = sourceHypoColl;
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}
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}
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SearchNormal::~SearchNormal()
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{
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RemoveAllInColl(m_hypoStackColl);
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}
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/**
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* Main decoder loop that translates a sentence by expanding
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* hypotheses stack by stack, until the end of the sentence.
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*/
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void SearchNormal::ProcessSentence()
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{
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const StaticData &staticData = StaticData::Instance();
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SentenceStats &stats = m_manager.GetSentenceStats();
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clock_t t=0; // used to track time for steps
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// initial seed hypothesis: nothing translated, no words produced
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Hypothesis *hypo = Hypothesis::Create(m_manager,m_source, m_initialTransOpt);
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m_hypoStackColl[0]->AddPrune(hypo);
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// go through each stack
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std::vector < HypothesisStack* >::iterator iterStack;
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for (iterStack = m_hypoStackColl.begin() ; iterStack != m_hypoStackColl.end() ; ++iterStack) {
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// check if decoding ran out of time
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double _elapsed_time = GetUserTime();
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if (_elapsed_time > staticData.GetTimeoutThreshold()) {
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VERBOSE(1,"Decoding is out of time (" << _elapsed_time << "," << staticData.GetTimeoutThreshold() << ")" << std::endl);
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interrupted_flag = 1;
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return;
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}
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HypothesisStackNormal &sourceHypoColl = *static_cast<HypothesisStackNormal*>(*iterStack);
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// the stack is pruned before processing (lazy pruning):
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VERBOSE(3,"processing hypothesis from next stack");
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IFVERBOSE(2) {
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t = clock();
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}
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sourceHypoColl.PruneToSize(staticData.GetMaxHypoStackSize());
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VERBOSE(3,std::endl);
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sourceHypoColl.CleanupArcList();
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IFVERBOSE(2) {
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stats.AddTimeStack( clock()-t );
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}
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// go through each hypothesis on the stack and try to expand it
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HypothesisStackNormal::const_iterator iterHypo;
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for (iterHypo = sourceHypoColl.begin() ; iterHypo != sourceHypoColl.end() ; ++iterHypo) {
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Hypothesis &hypothesis = **iterHypo;
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ProcessOneHypothesis(hypothesis); // expand the hypothesis
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}
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// some logging
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IFVERBOSE(2) {
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OutputHypoStackSize();
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}
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// this stack is fully expanded;
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actual_hypoStack = &sourceHypoColl;
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}
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// some more logging
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IFVERBOSE(2) {
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m_manager.GetSentenceStats().SetTimeTotal( clock()-m_start );
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}
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VERBOSE(2, m_manager.GetSentenceStats());
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}
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/** Find all translation options to expand one hypothesis, trigger expansion
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* this is mostly a check for overlap with already covered words, and for
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* violation of reordering limits.
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* \param hypothesis hypothesis to be expanded upon
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*/
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void SearchNormal::ProcessOneHypothesis(const Hypothesis &hypothesis)
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{
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// since we check for reordering limits, its good to have that limit handy
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int maxDistortion = StaticData::Instance().GetMaxDistortion();
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bool isWordLattice = StaticData::Instance().GetInputType() == WordLatticeInput;
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// no limit of reordering: only check for overlap
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if (maxDistortion < 0) {
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const WordsBitmap hypoBitmap = hypothesis.GetWordsBitmap();
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const size_t hypoFirstGapPos = hypoBitmap.GetFirstGapPos()
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, sourceSize = m_source.GetSize();
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for (size_t startPos = hypoFirstGapPos ; startPos < sourceSize ; ++startPos) {
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size_t maxSize = sourceSize - startPos;
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size_t maxSizePhrase = StaticData::Instance().GetMaxPhraseLength();
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maxSize = (maxSize < maxSizePhrase) ? maxSize : maxSizePhrase;
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for (size_t endPos = startPos ; endPos < startPos + maxSize ; ++endPos) {
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// basic checks
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// there have to be translation options
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if (m_transOptColl.GetTranslationOptionList(WordsRange(startPos, endPos)).size() == 0 ||
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// no overlap with existing words
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hypoBitmap.Overlap(WordsRange(startPos, endPos)) ||
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// specified reordering constraints (set with -monotone-at-punctuation or xml)
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!m_source.GetReorderingConstraint().Check( hypoBitmap, startPos, endPos ) ) {
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continue;
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}
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//TODO: does this method include incompatible WordLattice hypotheses?
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ExpandAllHypotheses(hypothesis, startPos, endPos);
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}
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}
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return; // done with special case (no reordering limit)
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}
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// if there are reordering limits, make sure it is not violated
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// the coverage bitmap is handy here (and the position of the first gap)
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const WordsBitmap hypoBitmap = hypothesis.GetWordsBitmap();
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const size_t hypoFirstGapPos = hypoBitmap.GetFirstGapPos()
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, sourceSize = m_source.GetSize();
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// MAIN LOOP. go through each possible range
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for (size_t startPos = hypoFirstGapPos ; startPos < sourceSize ; ++startPos) {
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// don't bother expanding phrases if the first position is already taken
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if(hypoBitmap.GetValue(startPos))
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continue;
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WordsRange prevRange = hypothesis.GetCurrSourceWordsRange();
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size_t maxSize = sourceSize - startPos;
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size_t maxSizePhrase = StaticData::Instance().GetMaxPhraseLength();
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maxSize = (maxSize < maxSizePhrase) ? maxSize : maxSizePhrase;
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size_t closestLeft = hypoBitmap.GetEdgeToTheLeftOf(startPos);
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if (isWordLattice) {
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// first question: is there a path from the closest translated word to the left
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// of the hypothesized extension to the start of the hypothesized extension?
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// long version: is there anything to our left? is it farther left than where we're starting anyway? can we get to it?
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// closestLeft is exclusive: a value of 3 means 2 is covered, our arc is currently ENDING at 3 and can start at 3 implicitly
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if (closestLeft != 0 && closestLeft != startPos && !m_source.CanIGetFromAToB(closestLeft, startPos)) {
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continue;
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}
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if (prevRange.GetStartPos() != NOT_FOUND &&
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prevRange.GetStartPos() > startPos && !m_source.CanIGetFromAToB(startPos, prevRange.GetStartPos())) {
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continue;
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}
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}
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WordsRange currentStartRange(startPos, startPos);
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if(m_source.ComputeDistortionDistance(prevRange, currentStartRange) > maxDistortion)
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continue;
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for (size_t endPos = startPos ; endPos < startPos + maxSize ; ++endPos) {
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// basic checks
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WordsRange extRange(startPos, endPos);
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// there have to be translation options
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if (m_transOptColl.GetTranslationOptionList(extRange).size() == 0 ||
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// no overlap with existing words
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hypoBitmap.Overlap(extRange) ||
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// specified reordering constraints (set with -monotone-at-punctuation or xml)
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!m_source.GetReorderingConstraint().Check( hypoBitmap, startPos, endPos ) || //
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// connection in input word lattice
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(isWordLattice && !m_source.IsCoveragePossible(extRange))) {
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continue;
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}
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// ask second question here:
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// we already know we can get to our starting point from the closest thing to the left. We now ask the follow up:
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// can we get from our end to the closest thing on the right?
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// long version: is anything to our right? is it farther right than our (inclusive) end? can our end reach it?
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bool leftMostEdge = (hypoFirstGapPos == startPos);
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// closest right definition:
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size_t closestRight = hypoBitmap.GetEdgeToTheRightOf(endPos);
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if (isWordLattice) {
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//if (!leftMostEdge && closestRight != endPos && closestRight != sourceSize && !m_source.CanIGetFromAToB(endPos, closestRight + 1)) {
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if (closestRight != endPos && ((closestRight + 1) < sourceSize) && !m_source.CanIGetFromAToB(endPos + 1, closestRight + 1)) {
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continue;
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}
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}
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// any length extension is okay if starting at left-most edge
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if (leftMostEdge) {
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ExpandAllHypotheses(hypothesis, startPos, endPos);
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}
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// starting somewhere other than left-most edge, use caution
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else {
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// the basic idea is this: we would like to translate a phrase starting
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// from a position further right than the left-most open gap. The
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// distortion penalty for the following phrase will be computed relative
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// to the ending position of the current extension, so we ask now what
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// its maximum value will be (which will always be the value of the
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// hypothesis starting at the left-most edge). If this value is less than
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// the distortion limit, we don't allow this extension to be made.
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WordsRange bestNextExtension(hypoFirstGapPos, hypoFirstGapPos);
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int required_distortion =
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m_source.ComputeDistortionDistance(extRange, bestNextExtension);
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if (required_distortion > maxDistortion) {
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continue;
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}
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// everything is fine, we're good to go
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ExpandAllHypotheses(hypothesis, startPos, endPos);
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}
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}
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}
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}
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/**
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* Expand a hypothesis given a list of translation options
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* \param hypothesis hypothesis to be expanded upon
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* \param startPos first word position of span covered
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* \param endPos last word position of span covered
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*/
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void SearchNormal::ExpandAllHypotheses(const Hypothesis &hypothesis, size_t startPos, size_t endPos)
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{
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// early discarding: check if hypothesis is too bad to build
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// this idea is explained in (Moore&Quirk, MT Summit 2007)
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float expectedScore = 0.0f;
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if (StaticData::Instance().UseEarlyDiscarding()) {
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// expected score is based on score of current hypothesis
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expectedScore = hypothesis.GetScore();
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// add new future score estimate
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expectedScore += m_transOptColl.GetFutureScore().CalcFutureScore( hypothesis.GetWordsBitmap(), startPos, endPos );
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}
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// loop through all translation options
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const TranslationOptionList &transOptList = m_transOptColl.GetTranslationOptionList(WordsRange(startPos, endPos));
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TranslationOptionList::const_iterator iter;
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for (iter = transOptList.begin() ; iter != transOptList.end() ; ++iter) {
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ExpandHypothesis(hypothesis, **iter, expectedScore);
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}
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}
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/**
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* Expand one hypothesis with a translation option.
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* this involves initial creation, scoring and adding it to the proper stack
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* \param hypothesis hypothesis to be expanded upon
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* \param transOpt translation option (phrase translation)
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* that is applied to create the new hypothesis
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* \param expectedScore base score for early discarding
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* (base hypothesis score plus future score estimation)
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*/
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void SearchNormal::ExpandHypothesis(const Hypothesis &hypothesis, const TranslationOption &transOpt, float expectedScore)
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{
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const StaticData &staticData = StaticData::Instance();
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SentenceStats &stats = m_manager.GetSentenceStats();
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clock_t t=0; // used to track time for steps
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Hypothesis *newHypo;
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if (! staticData.UseEarlyDiscarding()) {
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// simple build, no questions asked
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IFVERBOSE(2) {
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t = clock();
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}
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newHypo = hypothesis.CreateNext(transOpt);
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IFVERBOSE(2) {
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stats.AddTimeBuildHyp( clock()-t );
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}
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if (newHypo==NULL) return;
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newHypo->Evaluate(m_transOptColl.GetFutureScore());
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} else
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// early discarding: check if hypothesis is too bad to build
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{
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// worst possible score may have changed -> recompute
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size_t wordsTranslated = hypothesis.GetWordsBitmap().GetNumWordsCovered() + transOpt.GetSize();
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float allowedScore = m_hypoStackColl[wordsTranslated]->GetWorstScore();
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if (staticData.GetMinHypoStackDiversity()) {
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WordsBitmapID id = hypothesis.GetWordsBitmap().GetIDPlus(transOpt.GetStartPos(), transOpt.GetEndPos());
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float allowedScoreForBitmap = m_hypoStackColl[wordsTranslated]->GetWorstScoreForBitmap( id );
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allowedScore = std::min( allowedScore, allowedScoreForBitmap );
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}
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allowedScore += staticData.GetEarlyDiscardingThreshold();
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// add expected score of translation option
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expectedScore += transOpt.GetFutureScore();
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// TRACE_ERR("EXPECTED diff: " << (newHypo->GetTotalScore()-expectedScore) << " (pre " << (newHypo->GetTotalScore()-expectedScorePre) << ") " << hypothesis.GetTargetPhrase() << " ... " << transOpt.GetTargetPhrase() << " [" << expectedScorePre << "," << expectedScore << "," << newHypo->GetTotalScore() << "]" << endl);
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// check if transOpt score push it already below limit
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if (expectedScore < allowedScore) {
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IFVERBOSE(2) {
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stats.AddNotBuilt();
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}
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return;
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}
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// build the hypothesis without scoring
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IFVERBOSE(2) {
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t = clock();
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}
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newHypo = hypothesis.CreateNext(transOpt);
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if (newHypo==NULL) return;
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IFVERBOSE(2) {
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stats.AddTimeBuildHyp( clock()-t );
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}
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// ... and check if that is below the limit
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if (expectedScore < allowedScore) {
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IFVERBOSE(2) {
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stats.AddEarlyDiscarded();
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}
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FREEHYPO( newHypo );
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return;
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}
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}
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// logging for the curious
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IFVERBOSE(3) {
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newHypo->PrintHypothesis();
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}
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// add to hypothesis stack
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size_t wordsTranslated = newHypo->GetWordsBitmap().GetNumWordsCovered();
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IFVERBOSE(2) {
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t = clock();
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}
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m_hypoStackColl[wordsTranslated]->AddPrune(newHypo);
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IFVERBOSE(2) {
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stats.AddTimeStack( clock()-t );
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}
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}
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const std::vector < HypothesisStack* >& SearchNormal::GetHypothesisStacks() const
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{
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return m_hypoStackColl;
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}
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/**
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* Find best hypothesis on the last stack.
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* This is the end point of the best translation, which can be traced back from here
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*/
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const Hypothesis *SearchNormal::GetBestHypothesis() const
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{
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if (interrupted_flag == 0) {
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const HypothesisStackNormal &hypoColl = *static_cast<HypothesisStackNormal*>(m_hypoStackColl.back());
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return hypoColl.GetBestHypothesis();
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} else {
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const HypothesisStackNormal &hypoColl = *actual_hypoStack;
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return hypoColl.GetBestHypothesis();
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}
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}
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/**
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* Logging of hypothesis stack sizes
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*/
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void SearchNormal::OutputHypoStackSize()
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{
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std::vector < HypothesisStack* >::const_iterator iterStack = m_hypoStackColl.begin();
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TRACE_ERR( "Stack sizes: " << (int)(*iterStack)->size());
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for (++iterStack; iterStack != m_hypoStackColl.end() ; ++iterStack) {
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TRACE_ERR( ", " << (int)(*iterStack)->size());
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}
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TRACE_ERR( endl);
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}
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}
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