1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
|
/*
* File: lexdecom.cpp
* Author: Felipe Sánchez-Martínez, Universitat d'Alacant <fsanchez@dlsi.ua.es>
*
* Created on 2010/01/27
*/
#include "lexdecom.h"
#include "scorer-impl.h"
#include <iostream>
#include <fstream>
PhraseScorer*
LexicalDecompositionPhraseScorer::create_scorer(const char *argv[], int &argp, bool reverse, const PhraseScorerFactory &ptf)
{
if(argv[argp] == NULL)
usage();
String lwfile(argv[argp++]);
return new LexicalDecompositionPhraseScorer(ptf.get_phrase_table(), reverse, lwfile, argv, argp, ptf);
}
LexicalDecompositionPhraseScorer::LexicalDecompositionPhraseScorer(PhraseTable &pd, bool reverse,
const String &weightfile, const char *argv[], int &argp,
const PhraseScorerFactory &ptf) :
PhraseScorer(pd, reverse)
{
black_box_scorer = AbsoluteDiscountPhraseScorer::create_scorer(argv, argp, reverse, ptf);
std::ifstream wfile(weightfile.c_str());
//Code copied from LexicalWeightPhraseScorer; it should be factored !! -- 2010/01/27
std::cerr<<"Reading lexical weights from '"<<weightfile<<"' ... ";
while(!wfile.eof()) {
if(wfile.fail()) {
std::cerr << "Problem reading file: " << weightfile << std::endl;
exit(1);
}
String src, tgt;
Score weight;
wfile >> src >> tgt >> weight;
Count src_id = PhraseText::index_word(src);
Count tgt_id = PhraseText::index_word(tgt);
weight_map_.insert(std::make_pair(std::make_pair(src_id, tgt_id), weight));
}
wfile.close();
std::cerr<<"done."<<std::endl;
}
Score
LexicalDecompositionPhraseScorer::get_weight(const String &s_src, const String &s_tgt) const
{
//Code copied from LexicalWeightPhraseScorer; it should be factored !! -- 2010/01/27
Count src = PhraseText::index_word(s_src);
Count tgt = PhraseText::index_word(s_tgt);
return get_weight(src, tgt);
}
inline Score
LexicalDecompositionPhraseScorer::get_weight(Count src, Count tgt) const
{
//Code copied from LexicalWeightPhraseScorer; it should be factored !! -- 2010/01/27
WeightMapType_::const_iterator it = weight_map_.find(std::make_pair(src, tgt));
if(it == weight_map_.end())
return 0.00001; // default value copied from Philipp Koehn's scorer
return it->second;
}
void
LexicalDecompositionPhraseScorer::do_score_phrases()
{
//Estimate p(J|I) = p(src_len|tgt_len)
black_box_scorer->score_phrases();
std::cerr<<"LexicalDecompositionPhraseScorer::do_score_phrases"<<std::endl;
std::map<unsigned, std::map<unsigned, Count> > count_srclen_tgtlen;
std::map<unsigned, Count> total_tgtlen;
for(PhraseTable::iterator it = phrase_table_.begin(); it != phrase_table_.end(); it++) {
const PhrasePairInfo &ppair = *it;
PhraseInfo &src = phrase_table_.get_src_phrase(ppair.get_src());
PhraseInfo &tgt = phrase_table_.get_tgt_phrase(ppair.get_tgt());
unsigned src_len = src.get_phrase().size();
unsigned tgt_len = tgt.get_phrase().size();
/*//Debug code
for (unsigned i=0; i<src_len; i++)
std::cerr<<src.get_phrase().word(i)<<" ";
std::cerr<<"-> "<<src_len<<" ||| ";
for (unsigned i=0; i<tgt_len; i++)
std::cerr<<tgt.get_phrase().word(i)<<" ";
std::cerr<<"-> "<<tgt_len<<std::endl;
*/
count_srclen_tgtlen[src_len][tgt_len]+=ppair.get_count();
total_tgtlen[tgt_len]+=ppair.get_count();
}
std::map<unsigned, std::map<unsigned, Count> >::iterator its;
std::map<unsigned, Count>::iterator itt;
for (its=count_srclen_tgtlen.begin(); its!=count_srclen_tgtlen.end(); its++) {
unsigned src_len=its->first;
for(itt=its->second.begin(); itt!=its->second.end(); itt++) {
unsigned tgt_len=itt->first;
Count cnt=itt->second;
prob_srclen_tgtlen_[src_len][tgt_len] = static_cast<Score>(cnt)/static_cast<Score>(total_tgtlen[tgt_len]);
}
}
}
Score
LexicalDecompositionPhraseScorer::get_noisy_or_combination(Count src_word, PhraseInfo &tgt_phrase)
{
Score sc=1.0;
unsigned tgt_len=tgt_phrase.get_phrase().size();
for(unsigned i=0; i<tgt_len; i++) {
Count tgt_word=tgt_phrase.get_phrase()[i];
sc *= (1.0 - get_weight(src_word, tgt_word));
}
return (1.0 - sc);
}
Score
LexicalDecompositionPhraseScorer::do_get_score(const PhraseTable::const_iterator &it)
{
/*
The implementation of this method relies on the asumption that the
smoothed probabilities produced by AbsoluteDiscountPhraseScorer
are deficient.
*/
PhraseInfo &src_phrase = phrase_table_.get_src_phrase(it->get_src());
PhraseInfo &tgt_phrase = phrase_table_.get_tgt_phrase(it->get_tgt());
unsigned src_len=src_phrase.get_phrase().size();
unsigned tgt_len=tgt_phrase.get_phrase().size();
Score prod=1.0;
for(unsigned j=0; j<src_len; j++)
prod *= get_noisy_or_combination(src_phrase.get_phrase()[j], tgt_phrase);
Score lambda= static_cast<Score>(black_box_scorer->get_discount()) *
tgt_phrase.get_distinct() / tgt_phrase.get_count();
Score ret_value = black_box_scorer->get_score(it) + (lambda * prod * prob_srclen_tgtlen_[src_len][tgt_len]);
/*
//Debug code
for (unsigned i=0; i<src_len; i++)
std::cerr<<src_phrase.get_phrase().word(i)<<" ";
std::cerr<<" ||| ";
for (unsigned i=0; i<tgt_len; i++)
std::cerr<<tgt_phrase.get_phrase().word(i)<<" ";
std::cerr<<"==> discount: "<<black_box_scorer->get_discount()<<"; black box score: "<<black_box_scorer->get_score(it)
<<"; lambda: "<<lambda<<"; prod: "
<<prod<<"; prob_srclen_tgtlen_["<<src_len<<"]["<<tgt_len<<"]: "<<prob_srclen_tgtlen_[src_len][tgt_len]
<<"; count: "<<it->get_count()<<"; score: "<<ret_value;
std::cerr<<std::endl;
*/
return ret_value;
}
|
