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diff --git a/extractor/rule_factory.h b/extractor/rule_factory.h
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+#ifndef _RULE_FACTORY_H_
+#define _RULE_FACTORY_H_
+
+#include <memory>
+#include <vector>
+
+#include "matchings_trie.h"
+
+using namespace std;
+
+namespace extractor {
+
+class Alignment;
+class DataArray;
+class FastIntersector;
+class Grammar;
+class MatchingsFinder;
+class PhraseBuilder;
+class Precomputation;
+class Rule;
+class RuleExtractor;
+class Sampler;
+class Scorer;
+class State;
+class SuffixArray;
+class Vocabulary;
+
+/**
+ * Component containing most of the logic for extracting SCFG rules for a given
+ * sentence.
+ *
+ * Given a sentence (as a vector of word ids), this class constructs all the
+ * possible source phrases starting from this sentence. For each source phrase,
+ * it finds all its occurrences in the source data and samples some of these
+ * occurrences to extract aligned source-target phrase pairs. A trie cache is
+ * used to avoid unnecessary computations if a source phrase can be constructed
+ * more than once (e.g. some words occur more than once in the sentence).
+ */
+class HieroCachingRuleFactory {
+ public:
+  HieroCachingRuleFactory(
+      shared_ptr<SuffixArray> source_suffix_array,
+      shared_ptr<DataArray> target_data_array,
+      shared_ptr<Alignment> alignment,
+      const shared_ptr<Vocabulary>& vocabulary,
+      shared_ptr<Precomputation> precomputation,
+      shared_ptr<Scorer> scorer,
+      int min_gap_size,
+      int max_rule_span,
+      int max_nonterminals,
+      int max_rule_symbols,
+      int max_samples,
+      bool require_tight_phrases);
+
+  // For testing only.
+  HieroCachingRuleFactory(
+      shared_ptr<MatchingsFinder> finder,
+      shared_ptr<FastIntersector> fast_intersector,
+      shared_ptr<PhraseBuilder> phrase_builder,
+      shared_ptr<RuleExtractor> rule_extractor,
+      shared_ptr<Vocabulary> vocabulary,
+      shared_ptr<Sampler> sampler,
+      shared_ptr<Scorer> scorer,
+      int min_gap_size,
+      int max_rule_span,
+      int max_nonterminals,
+      int max_chunks,
+      int max_rule_symbols);
+
+  virtual ~HieroCachingRuleFactory();
+
+  // Constructs SCFG rules for a given sentence.
+  // (See class description for more details.)
+  virtual Grammar GetGrammar(const vector<int>& word_ids);
+
+ protected:
+  HieroCachingRuleFactory();
+
+ private:
+  // Checks if the phrase (if previously encountered) or its prefix have any
+  // occurrences in the source data.
+  bool CannotHaveMatchings(shared_ptr<TrieNode> node, int word_id);
+
+  // Checks if the phrase has previously been analyzed.
+  bool RequiresLookup(shared_ptr<TrieNode> node, int word_id);
+
+  // Creates a new state in the trie that corresponds to adding a trailing
+  // nonterminal to the current phrase.
+  void AddTrailingNonterminal(vector<int> symbols,
+                              const Phrase& prefix,
+                              const shared_ptr<TrieNode>& prefix_node,
+                              bool starts_with_x);
+
+  // Extends the current state by possibly adding a nonterminal followed by a
+  // terminal.
+  vector<State> ExtendState(const vector<int>& word_ids,
+                            const State& state,
+                            vector<int> symbols,
+                            const Phrase& phrase,
+                            const shared_ptr<TrieNode>& node);
+
+  shared_ptr<MatchingsFinder> matchings_finder;
+  shared_ptr<FastIntersector> fast_intersector;
+  shared_ptr<PhraseBuilder> phrase_builder;
+  shared_ptr<RuleExtractor> rule_extractor;
+  shared_ptr<Vocabulary> vocabulary;
+  shared_ptr<Sampler> sampler;
+  shared_ptr<Scorer> scorer;
+  int min_gap_size;
+  int max_rule_span;
+  int max_nonterminals;
+  int max_chunks;
+  int max_rule_symbols;
+};
+
+} // namespace extractor
+
+#endif