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
|
#include "hg_intersect.h"
#include <vector>
#include <tr1/unordered_map>
#include <boost/lexical_cast.hpp>
#include <boost/functional/hash.hpp>
#include "tdict.h"
#include "hg.h"
#include "trule.h"
#include "wordid.h"
#include "bottom_up_parser.h"
using boost::lexical_cast;
using namespace std::tr1;
using namespace std;
struct RuleFilter {
unordered_map<vector<WordID>, bool, boost::hash<vector<WordID> > > exists_;
bool true_lattice;
RuleFilter(const Lattice& target, int max_phrase_size) {
true_lattice = false;
for (int i = 0; i < target.size(); ++i) {
vector<WordID> phrase;
int lim = min(static_cast<int>(target.size()), i + max_phrase_size);
for (int j = i; j < lim; ++j) {
if (target[j].size() > 1) { true_lattice = true; break; }
phrase.push_back(target[j][0].label);
exists_[phrase] = true;
}
}
vector<WordID> sos(1, TD::Convert("<s>"));
exists_[sos] = true;
}
bool operator()(const TRule& r) const {
// TODO do some smarter filtering for lattices
if (true_lattice) return false; // don't filter "true lattice" input
const vector<WordID>& e = r.e();
for (int i = 0; i < e.size(); ++i) {
if (e[i] <= 0) continue;
vector<WordID> phrase;
for (int j = i; j < e.size(); ++j) {
if (e[j] <= 0) break;
phrase.push_back(e[j]);
if (exists_.count(phrase) == 0) return true;
}
}
return false;
}
};
static bool FastLinearIntersect(const Lattice& target, Hypergraph* hg) {
cerr << " Fast linear-chain intersection...\n";
vector<bool> prune(hg->edges_.size(), false);
set<int> cov;
for (int i = 0; i < prune.size(); ++i) {
Hypergraph::Edge& edge = hg->edges_[i];
if (edge.Arity() == 0) {
const int trg_index = edge.prev_i_;
const WordID trg = target[trg_index][0].label;
assert(edge.rule_->EWords() == 1);
prune[i] = (edge.rule_->e_[0] != trg);
if (!prune[i]) {
cov.insert(trg_index);
swap(edge.prev_i_, edge.i_);
swap(edge.prev_j_, edge.j_);
}
}
}
hg->PruneEdges(prune);
return (cov.size() == target.size());
}
bool HG::Intersect(const Lattice& target, Hypergraph* hg) {
// there are a number of faster algorithms available for restricted
// classes of hypergraph and/or target.
if (hg->IsLinearChain() && target.IsSentence())
return FastLinearIntersect(target, hg);
vector<bool> rem(hg->edges_.size(), false);
const RuleFilter filter(target, 15); // TODO make configurable
for (int i = 0; i < rem.size(); ++i)
rem[i] = filter(*hg->edges_[i].rule_);
hg->PruneEdges(rem);
const int nedges = hg->edges_.size();
const int nnodes = hg->nodes_.size();
TextGrammar* g = new TextGrammar;
GrammarPtr gp(g);
vector<int> cats(nnodes);
// each node in the translation forest becomes a "non-terminal" in the new
// grammar, create the labels here
for (int i = 0; i < nnodes; ++i)
cats[i] = TD::Convert("CAT_" + lexical_cast<string>(i)) * -1;
// construct the grammar
for (int i = 0; i < nedges; ++i) {
const Hypergraph::Edge& edge = hg->edges_[i];
const vector<WordID>& tgt = edge.rule_->e();
const vector<WordID>& src = edge.rule_->f();
TRulePtr rule(new TRule);
rule->prev_i = edge.i_;
rule->prev_j = edge.j_;
rule->lhs_ = cats[edge.head_node_];
vector<WordID>& f = rule->f_;
vector<WordID>& e = rule->e_;
f.resize(tgt.size()); // swap source and target, since the parser
e.resize(src.size()); // parses using the source side!
Hypergraph::TailNodeVector tn(edge.tail_nodes_.size());
int ntc = 0;
for (int j = 0; j < tgt.size(); ++j) {
const WordID& cur = tgt[j];
if (cur > 0) {
f[j] = cur;
} else {
tn[ntc++] = cur;
f[j] = cats[edge.tail_nodes_[-cur]];
}
}
ntc = 0;
for (int j = 0; j < src.size(); ++j) {
const WordID& cur = src[j];
if (cur > 0) {
e[j] = cur;
} else {
e[j] = tn[ntc++];
}
}
rule->scores_ = edge.feature_values_;
rule->parent_rule_ = edge.rule_;
rule->ComputeArity();
//cerr << "ADD: " << rule->AsString() << endl;
g->AddRule(rule);
}
g->SetMaxSpan(target.size() + 1);
const string& new_goal = TD::Convert(cats.back() * -1);
vector<GrammarPtr> grammars(1, gp);
Hypergraph tforest;
ExhaustiveBottomUpParser parser(new_goal, grammars);
if (!parser.Parse(target, &tforest))
return false;
else
hg->swap(tforest);
return true;
}
|
