source syntax features ~ blunsom emnlp 2008

4 files changed, 184 insertions, 0 deletions

diff --git a/decoder/Makefile.am b/decoder/Makefile.am
index e5f7505f..ede1cff0 100644
--- a/decoder/Makefile.am
+++ b/decoder/Makefile.am
@@ -72,6 +72,7 @@ libcdec_a_SOURCES = \
   ff_wordalign.cc \
   ff_csplit.cc \
   ff_tagger.cc \
+  ff_source_syntax.cc \
   ff_bleu.cc \
   ff_factory.cc \
   freqdict.cc \
diff --git a/decoder/cdec_ff.cc b/decoder/cdec_ff.cc
index 588842f1..d562bc3a 100644
--- a/decoder/cdec_ff.cc
+++ b/decoder/cdec_ff.cc
@@ -14,6 +14,7 @@
 #include "ff_bleu.h"
 #include "ff_lm_fsa.h"
 #include "ff_sample_fsa.h"
+#include "ff_source_syntax.h"
 #include "ff_register.h"
 #include "ff_charset.h"
 #include "ff_wordset.h"
@@ -55,6 +56,7 @@ void register_feature_functions() {
   ff_registry.Register("SpanFeatures", new FFFactory<SpanFeatures>());
   ff_registry.Register("NgramFeatures", new FFFactory<NgramDetector>());
   ff_registry.Register("RuleIdentityFeatures", new FFFactory<RuleIdentityFeatures>());
+  ff_registry.Register("SourceSyntaxFeatures", new FFFactory<SourceSyntaxFeatures>);
   ff_registry.Register("RuleNgramFeatures", new FFFactory<RuleNgramFeatures>());
   ff_registry.Register("CMR2008ReorderingFeatures", new FFFactory<CMR2008ReorderingFeatures>());
   ff_registry.Register("KLanguageModel", new KLanguageModelFactory());
diff --git a/decoder/ff_source_syntax.cc b/decoder/ff_source_syntax.cc
new file mode 100644
index 00000000..99acbd87
--- /dev/null
+++ b/decoder/ff_source_syntax.cc
@@ -0,0 +1,157 @@
+#include "ff_source_syntax.h"
+
+#include <sstream>
+#include <stack>
+
+#include "sentence_metadata.h"
+#include "array2d.h"
+#include "filelib.h"
+
+using namespace std;
+
+// implements the source side syntax features described in Blunsom et al. (EMNLP 2008)
+// source trees must be represented in Penn Treebank format, e.g.
+//     (S (NP John) (VP (V left)))
+
+struct SourceSyntaxFeaturesImpl {
+  SourceSyntaxFeaturesImpl() {}
+
+  void InitializeGrids(const string& tree, unsigned src_len) {
+    assert(tree.size() > 0);
+    fids_cat.clear();
+    fids_fonly.clear();
+    fids_ef.clear();
+    src_tree.clear();
+    fids_cat.resize(src_len, src_len + 1);
+    fids_fonly.resize(src_len, src_len + 1);
+    fids_ef.resize(src_len, src_len + 1);
+    src_tree.resize(src_len, src_len + 1, TD::Convert("XX"));
+    ParseTreeString(tree, src_len);
+  }
+
+  void ParseTreeString(const string& tree, unsigned src_len) {
+    stack<pair<int, WordID> > stk;  // first = i, second = category
+    pair<int, WordID> cur_cat; cur_cat.first = -1;
+    unsigned i = 0;
+    unsigned p = 0;
+    while(p < tree.size()) {
+      const char cur = tree[p];
+      if (cur == '(') {
+        stk.push(cur_cat);
+        ++p;
+        unsigned k = p + 1;
+        while (k < tree.size() && tree[k] != ' ') { ++k; }
+        cur_cat.first = i;
+        cur_cat.second = TD::Convert(tree.substr(p, k - p));
+        // cerr << "NT: '" << tree.substr(p, k-p) << "' (i=" << i << ")\n";
+        p = k + 1;
+      } else if (cur == ')') {
+        unsigned k = p;
+        while (k < tree.size() && tree[k] == ')') { ++k; }
+        const unsigned num_closes = k - p;
+        for (unsigned ci = 0; ci < num_closes; ++ci) {
+          // cur_cat.second spans from cur_cat.first to i
+          // cerr << TD::Convert(cur_cat.second) << " from " << cur_cat.first << " to " << i << endl;
+          // NOTE: unary rule chains end up being labeled with the top-most category
+          src_tree(cur_cat.first, i) = cur_cat.second;
+          cur_cat = stk.top();
+          stk.pop();
+        }
+        p = k;
+        while (p < tree.size() && (tree[p] == ' ' || tree[p] == '\t')) { ++p; }
+      } else if (cur == ' ' || cur == '\t') {
+        cerr << "Unexpected whitespace in: " << tree << endl;
+        abort();
+      } else { // terminal symbol
+        unsigned k = p + 1;
+        do {
+          while (k < tree.size() && tree[k] != ')' && tree[k] != ' ') { ++k; }
+          // cerr << "TERM: '" << tree.substr(p, k-p) << "' (i=" << i << ")\n";
+          ++i;
+          assert(i <= src_len);
+          while (k < tree.size() && tree[k] == ' ') { ++k; }
+          p = k;
+        } while (p < tree.size() && tree[p] != ')');
+      }
+    }
+    // cerr << "i=" << i << "  src_len=" << src_len << endl;
+    assert(i == src_len);  // make sure tree specified in src_tree is
+                           // the same length as the source sentence
+  }
+
+  WordID FireFeatures(const TRule& rule, const int i, const int j, const WordID* ants, SparseVector<double>* feats) {
+    //cerr << "fire features: " << rule.AsString() << " for " << i << "," << j << endl;
+    const WordID lhs = src_tree(i,j);
+    int& fid_cat = fids_cat(i,j);
+    int& fid_fonly = fids_fonly(i,j)[&rule];
+    int& fid_ef = fids_ef(i,j)[&rule];
+    if (fid_ef <= 0) {
+      ostringstream os;
+      os << "SYN:" << TD::Convert(lhs);
+      fid_cat = FD::Convert(os.str());
+      os << ':';
+      unsigned ntc = 0;
+      for (unsigned k = 0; k < rule.f_.size(); ++k) {
+        if (k > 0) os << '_';
+        int fj = rule.f_[k];
+        if (fj <= 0) {
+          os << '[' << TD::Convert(ants[ntc++]) << ']';
+        } else {
+          os << TD::Convert(fj);
+        }
+      }
+      fid_fonly = FD::Convert(os.str());
+      os << ':';
+      for (unsigned k = 0; k < rule.e_.size(); ++k) {
+        const int ei = rule.e_[k];
+        if (k > 0) os << '_';
+        if (ei <= 0)
+          os << '[' << (1-ei) << ']';
+        else
+          os << TD::Convert(ei);
+      }
+      fid_ef = FD::Convert(os.str());
+    }
+    if (fid_cat > 0)
+      feats->set_value(fid_cat, 1.0);
+    if (fid_fonly > 0)
+      feats->set_value(fid_fonly, 1.0);
+    if (fid_ef > 0)
+      feats->set_value(fid_ef, 1.0);
+    return lhs;
+  }
+
+  Array2D<WordID> src_tree;  // src_tree(i,j) NT = type
+  mutable Array2D<int> fids_cat;   // fires for an LHS match
+  mutable Array2D<map<const TRule*, int> > fids_fonly; // fires for an f-string
+  mutable Array2D<map<const TRule*, int> > fids_ef;    // fires for fully lexicalized
+};
+
+SourceSyntaxFeatures::SourceSyntaxFeatures(const string& param) :
+    FeatureFunction(sizeof(WordID)) {
+  impl = new SourceSyntaxFeaturesImpl;
+}
+
+SourceSyntaxFeatures::~SourceSyntaxFeatures() {
+  delete impl;
+  impl = NULL;
+}
+
+void SourceSyntaxFeatures::TraversalFeaturesImpl(const SentenceMetadata& smeta,
+                                     const Hypergraph::Edge& edge,
+                                     const vector<const void*>& ant_contexts,
+                                     SparseVector<double>* features,
+                                     SparseVector<double>* estimated_features,
+                                     void* context) const {
+  WordID ants[8];
+  for (unsigned i = 0; i < ant_contexts.size(); ++i)
+    ants[i] = *static_cast<const WordID*>(ant_contexts[i]);
+
+  *static_cast<WordID*>(context) =
+     impl->FireFeatures(*edge.rule_, edge.i_, edge.j_, ants, features);
+}
+
+void SourceSyntaxFeatures::PrepareForInput(const SentenceMetadata& smeta) {
+  impl->InitializeGrids(smeta.GetSGMLValue("src_tree"), smeta.GetSourceLength());
+}
+
diff --git a/decoder/ff_source_syntax.h b/decoder/ff_source_syntax.h
new file mode 100644
index 00000000..1e890736
--- /dev/null
+++ b/decoder/ff_source_syntax.h
@@ -0,0 +1,24 @@
+#ifndef _FF_SOURCE_TOOLS_H_
+#define _FF_SOURCE_TOOLS_H_
+
+#include "ff.h"
+
+struct SourceSyntaxFeaturesImpl;
+
+class SourceSyntaxFeatures : public FeatureFunction {
+ public:
+  SourceSyntaxFeatures(const std::string& param);
+  ~SourceSyntaxFeatures();
+ protected:
+  virtual void TraversalFeaturesImpl(const SentenceMetadata& smeta,
+                                     const Hypergraph::Edge& edge,
+                                     const std::vector<const void*>& ant_contexts,
+                                     SparseVector<double>* features,
+                                     SparseVector<double>* estimated_features,
+                                     void* context) const;
+  virtual void PrepareForInput(const SentenceMetadata& smeta);
+ private:
+  SourceSyntaxFeaturesImpl* impl;
+};
+
+#endif