Merge remote-tracking branch 'upstream/master'

23 files changed, 747 insertions, 0 deletions

diff --git a/extractor/features/count_source_target.cc b/extractor/features/count_source_target.cc
new file mode 100644
index 00000000..db0385e0
--- /dev/null
+++ b/extractor/features/count_source_target.cc
@@ -0,0 +1,17 @@
+#include "count_source_target.h"
+
+#include <cmath>
+
+namespace extractor {
+namespace features {
+
+double CountSourceTarget::Score(const FeatureContext& context) const {
+  return log10(1 + context.pair_count);
+}
+
+string CountSourceTarget::GetName() const {
+  return "CountEF";
+}
+
+} // namespace features
+} // namespace extractor
diff --git a/extractor/features/count_source_target.h b/extractor/features/count_source_target.h
new file mode 100644
index 00000000..8747fa60
--- /dev/null
+++ b/extractor/features/count_source_target.h
@@ -0,0 +1,22 @@
+#ifndef _COUNT_SOURCE_TARGET_H_
+#define _COUNT_SOURCE_TARGET_H_
+
+#include "feature.h"
+
+namespace extractor {
+namespace features {
+
+/**
+ * Feature for the number of times a word pair was found in the bitext.
+ */
+class CountSourceTarget : public Feature {
+ public:
+  double Score(const FeatureContext& context) const;
+
+  string GetName() const;
+};
+
+} // namespace features
+} // namespace extractor
+
+#endif
diff --git a/extractor/features/count_source_target_test.cc b/extractor/features/count_source_target_test.cc
new file mode 100644
index 00000000..1fd0c2aa
--- /dev/null
+++ b/extractor/features/count_source_target_test.cc
@@ -0,0 +1,36 @@
+#include <gtest/gtest.h>
+
+#include <memory>
+#include <string>
+
+#include "count_source_target.h"
+
+using namespace std;
+using namespace ::testing;
+
+namespace extractor {
+namespace features {
+namespace {
+
+class CountSourceTargetTest : public Test {
+ protected:
+  virtual void SetUp() {
+    feature = make_shared<CountSourceTarget>();
+  }
+
+  shared_ptr<CountSourceTarget> feature;
+};
+
+TEST_F(CountSourceTargetTest, TestGetName) {
+  EXPECT_EQ("CountEF", feature->GetName());
+}
+
+TEST_F(CountSourceTargetTest, TestScore) {
+  Phrase phrase;
+  FeatureContext context(phrase, phrase, 0.5, 9, 13);
+  EXPECT_EQ(1.0, feature->Score(context));
+}
+
+} // namespace
+} // namespace features
+} // namespace extractor
diff --git a/extractor/features/feature.cc b/extractor/features/feature.cc
new file mode 100644
index 00000000..939bcc59
--- /dev/null
+++ b/extractor/features/feature.cc
@@ -0,0 +1,11 @@
+#include "feature.h"
+
+namespace extractor {
+namespace features {
+
+const double Feature::MAX_SCORE = 99.0;
+
+Feature::~Feature() {}
+
+} // namespace features
+} // namespace extractor
diff --git a/extractor/features/feature.h b/extractor/features/feature.h
new file mode 100644
index 00000000..36ea504a
--- /dev/null
+++ b/extractor/features/feature.h
@@ -0,0 +1,47 @@
+#ifndef _FEATURE_H_
+#define _FEATURE_H_
+
+#include <string>
+
+#include "phrase.h"
+
+using namespace std;
+
+namespace extractor {
+namespace features {
+
+/**
+ * Structure providing context for computing feature scores.
+ */
+struct FeatureContext {
+  FeatureContext(const Phrase& source_phrase, const Phrase& target_phrase,
+                 double source_phrase_count, int pair_count, int num_samples) :
+    source_phrase(source_phrase), target_phrase(target_phrase),
+    source_phrase_count(source_phrase_count), pair_count(pair_count),
+    num_samples(num_samples) {}
+
+  Phrase source_phrase;
+  Phrase target_phrase;
+  double source_phrase_count;
+  int pair_count;
+  int num_samples;
+};
+
+/**
+ * Base class for features.
+ */
+class Feature {
+ public:
+  virtual double Score(const FeatureContext& context) const = 0;
+
+  virtual string GetName() const = 0;
+
+  virtual ~Feature();
+
+  static const double MAX_SCORE;
+};
+
+} // namespace features
+} // namespace extractor
+
+#endif
diff --git a/extractor/features/is_source_singleton.cc b/extractor/features/is_source_singleton.cc
new file mode 100644
index 00000000..1abb486f
--- /dev/null
+++ b/extractor/features/is_source_singleton.cc
@@ -0,0 +1,17 @@
+#include "is_source_singleton.h"
+
+#include <cmath>
+
+namespace extractor {
+namespace features {
+
+double IsSourceSingleton::Score(const FeatureContext& context) const {
+  return fabs(context.source_phrase_count - 1) < 1e-6;
+}
+
+string IsSourceSingleton::GetName() const {
+  return "IsSingletonF";
+}
+
+} // namespace features
+} // namespace extractor
diff --git a/extractor/features/is_source_singleton.h b/extractor/features/is_source_singleton.h
new file mode 100644
index 00000000..b8352d0e
--- /dev/null
+++ b/extractor/features/is_source_singleton.h
@@ -0,0 +1,22 @@
+#ifndef _IS_SOURCE_SINGLETON_H_
+#define _IS_SOURCE_SINGLETON_H_
+
+#include "feature.h"
+
+namespace extractor {
+namespace features {
+
+/**
+ * Boolean feature checking if the source phrase occurs only once in the data.
+ */
+class IsSourceSingleton : public Feature {
+ public:
+  double Score(const FeatureContext& context) const;
+
+  string GetName() const;
+};
+
+} // namespace features
+} // namespace extractor
+
+#endif
diff --git a/extractor/features/is_source_singleton_test.cc b/extractor/features/is_source_singleton_test.cc
new file mode 100644
index 00000000..f4266671
--- /dev/null
+++ b/extractor/features/is_source_singleton_test.cc
@@ -0,0 +1,39 @@
+#include <gtest/gtest.h>
+
+#include <memory>
+#include <string>
+
+#include "is_source_singleton.h"
+
+using namespace std;
+using namespace ::testing;
+
+namespace extractor {
+namespace features {
+namespace {
+
+class IsSourceSingletonTest : public Test {
+ protected:
+  virtual void SetUp() {
+    feature = make_shared<IsSourceSingleton>();
+  }
+
+  shared_ptr<IsSourceSingleton> feature;
+};
+
+TEST_F(IsSourceSingletonTest, TestGetName) {
+  EXPECT_EQ("IsSingletonF", feature->GetName());
+}
+
+TEST_F(IsSourceSingletonTest, TestScore) {
+  Phrase phrase;
+  FeatureContext context(phrase, phrase, 0.5, 3, 31);
+  EXPECT_EQ(0, feature->Score(context));
+
+  context = FeatureContext(phrase, phrase, 1, 3, 25);
+  EXPECT_EQ(1, feature->Score(context));
+}
+
+} // namespace
+} // namespace features
+} // namespace extractor
diff --git a/extractor/features/is_source_target_singleton.cc b/extractor/features/is_source_target_singleton.cc
new file mode 100644
index 00000000..03b3c62c
--- /dev/null
+++ b/extractor/features/is_source_target_singleton.cc
@@ -0,0 +1,17 @@
+#include "is_source_target_singleton.h"
+
+#include <cmath>
+
+namespace extractor {
+namespace features {
+
+double IsSourceTargetSingleton::Score(const FeatureContext& context) const {
+  return context.pair_count == 1;
+}
+
+string IsSourceTargetSingleton::GetName() const {
+  return "IsSingletonFE";
+}
+
+} // namespace features
+} // namespace extractor
diff --git a/extractor/features/is_source_target_singleton.h b/extractor/features/is_source_target_singleton.h
new file mode 100644
index 00000000..dacfebba
--- /dev/null
+++ b/extractor/features/is_source_target_singleton.h
@@ -0,0 +1,22 @@
+#ifndef _IS_SOURCE_TARGET_SINGLETON_H_
+#define _IS_SOURCE_TARGET_SINGLETON_H_
+
+#include "feature.h"
+
+namespace extractor {
+namespace features {
+
+/**
+ * Boolean feature checking if the phrase pair occurs only once in the data.
+ */
+class IsSourceTargetSingleton : public Feature {
+ public:
+  double Score(const FeatureContext& context) const;
+
+  string GetName() const;
+};
+
+} // namespace features
+} // namespace extractor
+
+#endif
diff --git a/extractor/features/is_source_target_singleton_test.cc b/extractor/features/is_source_target_singleton_test.cc
new file mode 100644
index 00000000..929635b0
--- /dev/null
+++ b/extractor/features/is_source_target_singleton_test.cc
@@ -0,0 +1,39 @@
+#include <gtest/gtest.h>
+
+#include <memory>
+#include <string>
+
+#include "is_source_target_singleton.h"
+
+using namespace std;
+using namespace ::testing;
+
+namespace extractor {
+namespace features {
+namespace {
+
+class IsSourceTargetSingletonTest : public Test {
+ protected:
+  virtual void SetUp() {
+    feature = make_shared<IsSourceTargetSingleton>();
+  }
+
+  shared_ptr<IsSourceTargetSingleton> feature;
+};
+
+TEST_F(IsSourceTargetSingletonTest, TestGetName) {
+  EXPECT_EQ("IsSingletonFE", feature->GetName());
+}
+
+TEST_F(IsSourceTargetSingletonTest, TestScore) {
+  Phrase phrase;
+  FeatureContext context(phrase, phrase, 0.5, 3, 7);
+  EXPECT_EQ(0, feature->Score(context));
+
+  context = FeatureContext(phrase, phrase, 2.3, 1, 28);
+  EXPECT_EQ(1, feature->Score(context));
+}
+
+} // namespace
+} // namespace features
+} // namespace extractor
diff --git a/extractor/features/max_lex_source_given_target.cc b/extractor/features/max_lex_source_given_target.cc
new file mode 100644
index 00000000..65d0ec68
--- /dev/null
+++ b/extractor/features/max_lex_source_given_target.cc
@@ -0,0 +1,37 @@
+#include "max_lex_source_given_target.h"
+
+#include <cmath>
+
+#include "data_array.h"
+#include "translation_table.h"
+
+namespace extractor {
+namespace features {
+
+MaxLexSourceGivenTarget::MaxLexSourceGivenTarget(
+    shared_ptr<TranslationTable> table) :
+    table(table) {}
+
+double MaxLexSourceGivenTarget::Score(const FeatureContext& context) const {
+  vector<string> source_words = context.source_phrase.GetWords();
+  vector<string> target_words = context.target_phrase.GetWords();
+  target_words.push_back(DataArray::NULL_WORD_STR);
+
+  double score = 0;
+  for (string source_word: source_words) {
+    double max_score = 0;
+    for (string target_word: target_words) {
+      max_score = max(max_score,
+          table->GetSourceGivenTargetScore(source_word, target_word));
+    }
+    score += max_score > 0 ? -log10(max_score) : MAX_SCORE;
+  }
+  return score;
+}
+
+string MaxLexSourceGivenTarget::GetName() const {
+  return "MaxLexFgivenE";
+}
+
+} // namespace features
+} // namespace extractor
diff --git a/extractor/features/max_lex_source_given_target.h b/extractor/features/max_lex_source_given_target.h
new file mode 100644
index 00000000..461b0ebf
--- /dev/null
+++ b/extractor/features/max_lex_source_given_target.h
@@ -0,0 +1,34 @@
+#ifndef _MAX_LEX_SOURCE_GIVEN_TARGET_H_
+#define _MAX_LEX_SOURCE_GIVEN_TARGET_H_
+
+#include <memory>
+
+#include "feature.h"
+
+using namespace std;
+
+namespace extractor {
+
+class TranslationTable;
+
+namespace features {
+
+/**
+ * Feature computing max(p(f | e)) across all pairs of words in the phrase pair.
+ */
+class MaxLexSourceGivenTarget : public Feature {
+ public:
+  MaxLexSourceGivenTarget(shared_ptr<TranslationTable> table);
+
+  double Score(const FeatureContext& context) const;
+
+  string GetName() const;
+
+ private:
+  shared_ptr<TranslationTable> table;
+};
+
+} // namespace features
+} // namespace extractor
+
+#endif
diff --git a/extractor/features/max_lex_source_given_target_test.cc b/extractor/features/max_lex_source_given_target_test.cc
new file mode 100644
index 00000000..7f6aae41
--- /dev/null
+++ b/extractor/features/max_lex_source_given_target_test.cc
@@ -0,0 +1,78 @@
+#include <gtest/gtest.h>
+
+#include <cmath>
+#include <memory>
+#include <string>
+
+#include "data_array.h"
+#include "mocks/mock_translation_table.h"
+#include "mocks/mock_vocabulary.h"
+#include "phrase_builder.h"
+#include "max_lex_source_given_target.h"
+
+using namespace std;
+using namespace ::testing;
+
+namespace extractor {
+namespace features {
+namespace {
+
+class MaxLexSourceGivenTargetTest : public Test {
+ protected:
+  virtual void SetUp() {
+    vector<string> source_words = {"f1", "f2", "f3"};
+    vector<string> target_words = {"e1", "e2", "e3"};
+
+    vocabulary = make_shared<MockVocabulary>();
+    for (size_t i = 0; i < source_words.size(); ++i) {
+      EXPECT_CALL(*vocabulary, GetTerminalValue(i))
+          .WillRepeatedly(Return(source_words[i]));
+    }
+    for (size_t i = 0; i < target_words.size(); ++i) {
+      EXPECT_CALL(*vocabulary, GetTerminalValue(i + source_words.size()))
+          .WillRepeatedly(Return(target_words[i]));
+    }
+
+    phrase_builder = make_shared<PhraseBuilder>(vocabulary);
+
+    table = make_shared<MockTranslationTable>();
+    for (size_t i = 0; i < source_words.size(); ++i) {
+      for (size_t j = 0; j < target_words.size(); ++j) {
+        int value = i - j;
+        EXPECT_CALL(*table, GetSourceGivenTargetScore(
+            source_words[i], target_words[j])).WillRepeatedly(Return(value));
+      }
+    }
+
+    for (size_t i = 0; i < source_words.size(); ++i) {
+      int value = i * 3;
+      EXPECT_CALL(*table, GetSourceGivenTargetScore(
+          source_words[i], DataArray::NULL_WORD_STR))
+          .WillRepeatedly(Return(value));
+    }
+
+    feature = make_shared<MaxLexSourceGivenTarget>(table);
+  }
+
+  shared_ptr<MockVocabulary> vocabulary;
+  shared_ptr<PhraseBuilder> phrase_builder;
+  shared_ptr<MockTranslationTable> table;
+  shared_ptr<MaxLexSourceGivenTarget> feature;
+};
+
+TEST_F(MaxLexSourceGivenTargetTest, TestGetName) {
+  EXPECT_EQ("MaxLexFgivenE", feature->GetName());
+}
+
+TEST_F(MaxLexSourceGivenTargetTest, TestScore) {
+  vector<int> source_symbols = {0, 1, 2};
+  Phrase source_phrase = phrase_builder->Build(source_symbols);
+  vector<int> target_symbols = {3, 4, 5};
+  Phrase target_phrase = phrase_builder->Build(target_symbols);
+  FeatureContext context(source_phrase, target_phrase, 0.3, 7, 11);
+  EXPECT_EQ(99 - log10(18), feature->Score(context));
+}
+
+} // namespace
+} // namespace features
+} // namespace extractor
diff --git a/extractor/features/max_lex_target_given_source.cc b/extractor/features/max_lex_target_given_source.cc
new file mode 100644
index 00000000..33783054
--- /dev/null
+++ b/extractor/features/max_lex_target_given_source.cc
@@ -0,0 +1,37 @@
+#include "max_lex_target_given_source.h"
+
+#include <cmath>
+
+#include "data_array.h"
+#include "translation_table.h"
+
+namespace extractor {
+namespace features {
+
+MaxLexTargetGivenSource::MaxLexTargetGivenSource(
+    shared_ptr<TranslationTable> table) :
+    table(table) {}
+
+double MaxLexTargetGivenSource::Score(const FeatureContext& context) const {
+  vector<string> source_words = context.source_phrase.GetWords();
+  source_words.push_back(DataArray::NULL_WORD_STR);
+  vector<string> target_words = context.target_phrase.GetWords();
+
+  double score = 0;
+  for (string target_word: target_words) {
+    double max_score = 0;
+    for (string source_word: source_words) {
+      max_score = max(max_score,
+          table->GetTargetGivenSourceScore(source_word, target_word));
+    }
+    score += max_score > 0 ? -log10(max_score) : MAX_SCORE;
+  }
+  return score;
+}
+
+string MaxLexTargetGivenSource::GetName() const {
+  return "MaxLexEgivenF";
+}
+
+} // namespace features
+} // namespace extractor
diff --git a/extractor/features/max_lex_target_given_source.h b/extractor/features/max_lex_target_given_source.h
new file mode 100644
index 00000000..c3c87327
--- /dev/null
+++ b/extractor/features/max_lex_target_given_source.h
@@ -0,0 +1,34 @@
+#ifndef _MAX_LEX_TARGET_GIVEN_SOURCE_H_
+#define _MAX_LEX_TARGET_GIVEN_SOURCE_H_
+
+#include <memory>
+
+#include "feature.h"
+
+using namespace std;
+
+namespace extractor {
+
+class TranslationTable;
+
+namespace features {
+
+/**
+ * Feature computing max(p(e | f)) across all pairs of words in the phrase pair.
+ */
+class MaxLexTargetGivenSource : public Feature {
+ public:
+  MaxLexTargetGivenSource(shared_ptr<TranslationTable> table);
+
+  double Score(const FeatureContext& context) const;
+
+  string GetName() const;
+
+ private:
+  shared_ptr<TranslationTable> table;
+};
+
+} // namespace features
+} // namespace extractor
+
+#endif
diff --git a/extractor/features/max_lex_target_given_source_test.cc b/extractor/features/max_lex_target_given_source_test.cc
new file mode 100644
index 00000000..6d0efd9c
--- /dev/null
+++ b/extractor/features/max_lex_target_given_source_test.cc
@@ -0,0 +1,78 @@
+#include <gtest/gtest.h>
+
+#include <cmath>
+#include <memory>
+#include <string>
+
+#include "data_array.h"
+#include "mocks/mock_translation_table.h"
+#include "mocks/mock_vocabulary.h"
+#include "phrase_builder.h"
+#include "max_lex_target_given_source.h"
+
+using namespace std;
+using namespace ::testing;
+
+namespace extractor {
+namespace features {
+namespace {
+
+class MaxLexTargetGivenSourceTest : public Test {
+ protected:
+  virtual void SetUp() {
+    vector<string> source_words = {"f1", "f2", "f3"};
+    vector<string> target_words = {"e1", "e2", "e3"};
+
+    vocabulary = make_shared<MockVocabulary>();
+    for (size_t i = 0; i < source_words.size(); ++i) {
+      EXPECT_CALL(*vocabulary, GetTerminalValue(i))
+          .WillRepeatedly(Return(source_words[i]));
+    }
+    for (size_t i = 0; i < target_words.size(); ++i) {
+      EXPECT_CALL(*vocabulary, GetTerminalValue(i + source_words.size()))
+          .WillRepeatedly(Return(target_words[i]));
+    }
+
+    phrase_builder = make_shared<PhraseBuilder>(vocabulary);
+
+    table = make_shared<MockTranslationTable>();
+    for (size_t i = 0; i < source_words.size(); ++i) {
+      for (size_t j = 0; j < target_words.size(); ++j) {
+        int value = i - j;
+        EXPECT_CALL(*table, GetTargetGivenSourceScore(
+            source_words[i], target_words[j])).WillRepeatedly(Return(value));
+      }
+    }
+
+    for (size_t i = 0; i < target_words.size(); ++i) {
+      int value = i * 3;
+      EXPECT_CALL(*table, GetTargetGivenSourceScore(
+          DataArray::NULL_WORD_STR, target_words[i]))
+          .WillRepeatedly(Return(value));
+    }
+
+    feature = make_shared<MaxLexTargetGivenSource>(table);
+  }
+
+  shared_ptr<MockVocabulary> vocabulary;
+  shared_ptr<PhraseBuilder> phrase_builder;
+  shared_ptr<MockTranslationTable> table;
+  shared_ptr<MaxLexTargetGivenSource> feature;
+};
+
+TEST_F(MaxLexTargetGivenSourceTest, TestGetName) {
+  EXPECT_EQ("MaxLexEgivenF", feature->GetName());
+}
+
+TEST_F(MaxLexTargetGivenSourceTest, TestScore) {
+  vector<int> source_symbols = {0, 1, 2};
+  Phrase source_phrase = phrase_builder->Build(source_symbols);
+  vector<int> target_symbols = {3, 4, 5};
+  Phrase target_phrase = phrase_builder->Build(target_symbols);
+  FeatureContext context(source_phrase, target_phrase, 0.3, 7, 19);
+  EXPECT_EQ(-log10(36), feature->Score(context));
+}
+
+} // namespace
+} // namespace features
+} // namespace extractor
diff --git a/extractor/features/sample_source_count.cc b/extractor/features/sample_source_count.cc
new file mode 100644
index 00000000..b110fc51
--- /dev/null
+++ b/extractor/features/sample_source_count.cc
@@ -0,0 +1,17 @@
+#include "sample_source_count.h"
+
+#include <cmath>
+
+namespace extractor {
+namespace features {
+
+double SampleSourceCount::Score(const FeatureContext& context) const {
+  return log10(1 + context.num_samples);
+}
+
+string SampleSourceCount::GetName() const {
+  return "SampleCountF";
+}
+
+} // namespace features
+} // namespace extractor
diff --git a/extractor/features/sample_source_count.h b/extractor/features/sample_source_count.h
new file mode 100644
index 00000000..ee6e59a0
--- /dev/null
+++ b/extractor/features/sample_source_count.h
@@ -0,0 +1,23 @@
+#ifndef _SAMPLE_SOURCE_COUNT_H_
+#define _SAMPLE_SOURCE_COUNT_H_
+
+#include "feature.h"
+
+namespace extractor {
+namespace features {
+
+/**
+ * Feature scoring the number of times the source phrase occurs in the sampled
+ * set.
+ */
+class SampleSourceCount : public Feature {
+ public:
+  double Score(const FeatureContext& context) const;
+
+  string GetName() const;
+};
+
+} // namespace features
+} // namespace extractor
+
+#endif
diff --git a/extractor/features/sample_source_count_test.cc b/extractor/features/sample_source_count_test.cc
new file mode 100644
index 00000000..63856b9d
--- /dev/null
+++ b/extractor/features/sample_source_count_test.cc
@@ -0,0 +1,40 @@
+#include <gtest/gtest.h>
+
+#include <cmath>
+#include <memory>
+#include <string>
+
+#include "sample_source_count.h"
+
+using namespace std;
+using namespace ::testing;
+
+namespace extractor {
+namespace features {
+namespace {
+
+class SampleSourceCountTest : public Test {
+ protected:
+  virtual void SetUp() {
+    feature = make_shared<SampleSourceCount>();
+  }
+
+  shared_ptr<SampleSourceCount> feature;
+};
+
+TEST_F(SampleSourceCountTest, TestGetName) {
+  EXPECT_EQ("SampleCountF", feature->GetName());
+}
+
+TEST_F(SampleSourceCountTest, TestScore) {
+  Phrase phrase;
+  FeatureContext context(phrase, phrase, 0, 3, 1);
+  EXPECT_EQ(log10(2), feature->Score(context));
+
+  context = FeatureContext(phrase, phrase, 3.2, 3, 9);
+  EXPECT_EQ(1.0, feature->Score(context));
+}
+
+} // namespace
+} // namespace features
+} // namespace extractor
diff --git a/extractor/features/target_given_source_coherent.cc b/extractor/features/target_given_source_coherent.cc
new file mode 100644
index 00000000..c4551d88
--- /dev/null
+++ b/extractor/features/target_given_source_coherent.cc
@@ -0,0 +1,18 @@
+#include "target_given_source_coherent.h"
+
+#include <cmath>
+
+namespace extractor {
+namespace features {
+
+double TargetGivenSourceCoherent::Score(const FeatureContext& context) const {
+  double prob = (double) context.pair_count / context.num_samples;
+  return prob > 0 ? -log10(prob) : MAX_SCORE;
+}
+
+string TargetGivenSourceCoherent::GetName() const {
+  return "EgivenFCoherent";
+}
+
+} // namespace features
+} // namespace extractor
diff --git a/extractor/features/target_given_source_coherent.h b/extractor/features/target_given_source_coherent.h
new file mode 100644
index 00000000..e66d70a5
--- /dev/null
+++ b/extractor/features/target_given_source_coherent.h
@@ -0,0 +1,23 @@
+#ifndef _TARGET_GIVEN_SOURCE_COHERENT_H_
+#define _TARGET_GIVEN_SOURCE_COHERENT_H_
+
+#include "feature.h"
+
+namespace extractor {
+namespace features {
+
+/**
+ * Feature computing the ratio of the phrase pair count over all source phrase
+ * occurrences (sampled).
+ */
+class TargetGivenSourceCoherent : public Feature {
+ public:
+  double Score(const FeatureContext& context) const;
+
+  string GetName() const;
+};
+
+} // namespace features
+} // namespace extractor
+
+#endif
diff --git a/extractor/features/target_given_source_coherent_test.cc b/extractor/features/target_given_source_coherent_test.cc
new file mode 100644
index 00000000..454105e1
--- /dev/null
+++ b/extractor/features/target_given_source_coherent_test.cc
@@ -0,0 +1,39 @@
+#include <gtest/gtest.h>
+
+#include <memory>
+#include <string>
+
+#include "target_given_source_coherent.h"
+
+using namespace std;
+using namespace ::testing;
+
+namespace extractor {
+namespace features {
+namespace {
+
+class TargetGivenSourceCoherentTest : public Test {
+ protected:
+  virtual void SetUp() {
+    feature = make_shared<TargetGivenSourceCoherent>();
+  }
+
+  shared_ptr<TargetGivenSourceCoherent> feature;
+};
+
+TEST_F(TargetGivenSourceCoherentTest, TestGetName) {
+  EXPECT_EQ("EgivenFCoherent", feature->GetName());
+}
+
+TEST_F(TargetGivenSourceCoherentTest, TestScore) {
+  Phrase phrase;
+  FeatureContext context(phrase, phrase, 0.3, 2, 20);
+  EXPECT_EQ(1.0, feature->Score(context));
+
+  context = FeatureContext(phrase, phrase, 1.9, 0, 1);
+  EXPECT_EQ(99.0, feature->Score(context));
+}
+
+} // namespace
+} // namespace features
+} // namespace extractor