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diff --git a/src/storage/ngram.h b/src/storage/ngram.h
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+/* 
+ *  novel-pinyin,
+ *  A Simplified Chinese Sentence-Based Pinyin Input Method Engine
+ *  Based On Markov Model.
+ *  
+ *  Copyright (C) 2006-2007 Peng Wu
+ *  
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ * 
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ *  GNU General Public License for more details.
+ *  
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program; if not, write to the Free Software
+ *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#ifndef NGRAM_H
+#define NGRAM_H
+
+#include <db.h>
+
+namespace novel{
+
+class Bigram;
+
+/* Note:
+ * When transfer from system ngram to user ngram, 
+ *   if user ngram doesn't exist,
+ *     copy total freq from system ngram to user ngram,
+ *     so the total freq exists.
+ *   if item freq don't exist, copy item freq from system to user ngram,
+ *     so the item freq exists.
+ *     if user ngram already exists(always true), increases the total freq,
+ *     if item ngram already exists(always true), increases the freq.
+ */
+
+class SingleGram{
+    friend class Bigram;
+private:
+    MemoryChunk m_chunk;
+    SingleGram(void * buffer, size_t length);
+public:
+    /* Null Constructor */
+    SingleGram();
+    /* search method */
+    /* the array result contains many items */
+    bool search(/* in */ PhraseIndexRange * range, 
+	       /* out */ BigramPhraseArray array);
+
+    bool get_freq(/* in */ phrase_token_t token,
+	       /* out */ guint32 & freq); 
+    
+    /* set_freq method
+     */
+    bool set_freq(/* in */ phrase_token_t token,
+		  guint32 freq);
+
+    /* set_total_freq method
+     * used in user bigram table
+     */
+    bool set_total_freq(guint32 m_total);
+    
+    /* get_total_freq method
+     * used in user bigram table
+     */
+    bool get_total_freq(guint32 & m_total);
+    
+    /* prune one method
+     * only used in training
+     */
+    bool prune();
+};
+
+class Bigram{
+private:
+    DB * m_system;
+    DB * m_user;
+public:
+    Bigram(){
+	m_system = NULL; m_user = NULL;
+    }
+
+    ~Bigram(){
+	reset();
+    }
+
+    void reset(){
+	if ( m_system ){
+	    m_system->close(m_system, 0);
+	    m_system = NULL;
+	}
+	if ( m_user ){
+	    m_user->close(m_user, 0);
+	    m_user = NULL;
+	}
+    }
+    
+    /* attach system and user bi-gram */
+    /* when with training systemdb is NULL, only user_gram */
+    bool attach(const char * systemfile, const char * userfile);
+
+    bool load(phrase_token_t index, SingleGram * & system_gram, SingleGram * & user_gram);
+    bool store(phrase_token_t index, SingleGram * user_gram);
+    /* array of phrase_token_t items, for parameter estimation. */
+    bool get_all_items(GArray * system, GArray * user);
+};
+
+};
+
+using namespace novel;
+
+
+#endif