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#include "tagger.h"
#include "tdict.h"
#include "hg_io.h"
#include "filelib.h"
#include "hg.h"
#include "wordid.h"
#include "sentence_metadata.h"
using namespace std;
// This is a really simple linear chain tagger.
// You specify a tagset, and it hypothesizes that each word in the
// input can be tagged with any member of the tagset.
// The are a couple sample features implemented in ff_tagger.h/cc
// One thing to note, that while CRFs typically define the label
// sequence as corresponding to the hidden states in a trellis,
// in our model the labels are on edges, but mathematically
// they are identical.
//
// Things to do if you want to make this a "real" tagger:
// - support dictionaries (for each word, limit the tags considered)
// - add latent variables - this is really easy to do
static void ReadTagset(const string& file, vector<WordID>* tags) {
ReadFile rf(file);
istream& in(*rf.stream());
while(in) {
string tag;
in >> tag;
if (tag.empty()) continue;
tags->push_back(TD::Convert(tag));
}
cerr << "Read " << tags->size() << " labels (tags) from " << file << endl;
}
struct TaggerImpl {
TaggerImpl(const boost::program_options::variables_map& conf) :
kXCAT(TD::Convert("X")*-1),
kNULL(TD::Convert("<eps>")),
kBINARY(new TRule("[X] ||| [X,1] [X,2] ||| [1] [2]")),
kGOAL_RULE(new TRule("[Goal] ||| [X,1] ||| [1]")) {
if (conf.count("tagger_tagset") == 0) {
cerr << "Tagger requires --tagger_tagset FILE!\n";
exit(1);
}
ReadTagset(conf["tagger_tagset"].as<string>(), &tagset_);
}
void BuildTrellis(const vector<WordID>& seq, Hypergraph* forest) {
int prev_node_id = -1;
for (int i = 0; i < seq.size(); ++i) {
const WordID& src = seq[i];
const int new_node_id = forest->AddNode(kXCAT)->id_;
for (int k = 0; k < tagset_.size(); ++k) {
TRulePtr rule(TRule::CreateLexicalRule(src, tagset_[k]));
Hypergraph::Edge* edge = forest->AddEdge(rule, Hypergraph::TailNodeVector());
edge->i_ = i;
edge->j_ = i+1;
edge->prev_i_ = i; // we set these for FastLinearIntersect
edge->prev_j_ = i+1; // " " "
forest->ConnectEdgeToHeadNode(edge->id_, new_node_id);
}
if (prev_node_id >= 0) {
const int comb_node_id = forest->AddNode(kXCAT)->id_;
Hypergraph::TailNodeVector tail(2, prev_node_id);
tail[1] = new_node_id;
Hypergraph::Edge* edge = forest->AddEdge(kBINARY, tail);
edge->i_ = 0;
edge->j_ = i+1;
forest->ConnectEdgeToHeadNode(edge->id_, comb_node_id);
prev_node_id = comb_node_id;
} else {
prev_node_id = new_node_id;
}
}
Hypergraph::TailNodeVector tail(1, forest->nodes_.size() - 1);
Hypergraph::Node* goal = forest->AddNode(TD::Convert("Goal")*-1);
Hypergraph::Edge* hg_edge = forest->AddEdge(kGOAL_RULE, tail);
forest->ConnectEdgeToHeadNode(hg_edge, goal);
}
private:
vector<WordID> tagset_;
const WordID kXCAT;
const WordID kNULL;
const TRulePtr kBINARY;
const TRulePtr kGOAL_RULE;
};
Tagger::Tagger(const boost::program_options::variables_map& conf) :
pimpl_(new TaggerImpl(conf)) {}
bool Tagger::Translate(const string& input,
SentenceMetadata* smeta,
const vector<double>& weights,
Hypergraph* forest) {
Lattice lattice;
LatticeTools::ConvertTextToLattice(input, &lattice);
smeta->SetSourceLength(lattice.size());
vector<WordID> sequence(lattice.size());
for (int i = 0; i < lattice.size(); ++i) {
assert(lattice[i].size() == 1);
sequence[i] = lattice[i][0].label;
}
pimpl_->BuildTrellis(sequence, forest);
forest->Reweight(weights);
forest->is_linear_chain_ = true;
return true;
}
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