diff --git a/include/object-db-file.h b/include/object-db-file.h
new file mode 100644
index 0000000..fb9ca91
--- /dev/null
+++ b/include/object-db-file.h
@@ -0,0 +1,143 @@
+#ifndef OBJECT_DB_FILE_H
+#define OBJECT_DB_FILE_H
+
+#include "object-db.h"
+#include <stdio.h>
+#include <fstream>
+#include <ifstream>
+#include <ofstream>
+#include <sstream>
+#include <boost/thread/locks.hpp>
+#include <boost/thread/recursive_mutex.hpp>
+#include <boost/lexical_cast.hpp>
+
+#define _OVERRIDE
+#ifdef __GNUC__
+#if __GNUC_MAJOR >= 4 && __GNUC_MINOR__ >= 7
+  #undef _OVERRIDE
+  #define _OVERRIDE override
+#endif // __GNUC__ version
+#endif // __GNUC__
+
+using namespace std;
+
+// This is a file based ObjectDB implementation
+// The assumption is, the Content Objects will be stored sequentially
+
+// To provide random access, we will have a table of "address" for each
+// ContentObject at the beginning of the file.
+// This also requires another assumption, that is the number of COs must
+// be know a priori. This requirement is reasonable for our dropbox-like
+// System, as the file we publish is static file and we can easily know
+// the number of COs before we store them into ObjectDB.
+
+/* How file looks like:
+ * |MAGIC_NUM|capacity|size|pos for each CO ...|1st CO|2nd CO| ... |
+ */
+
+class ObjectDBFile
+{
+public:
+  typedef boost::shared_mutex Lock;
+  typedef boost::unique_lock<Lock> WriteLock;
+  typedef boost::shared_lock<Lock> ReadLock;
+
+  ObjectDBFile(const string &filename);
+  virtual ~ObjectDBFile(){}
+
+  // reserve the "address" table for n COs; must reserve before
+  // write anything (unless reserved quota has not be consumed yet)
+  void
+  init(int capacity);
+
+  bool
+  initialized() const { return m_initialized; }
+
+  // assume sequential
+  virtual void
+  append(const Bytes &co) _OVERRIDE;
+
+  // get next CO
+  virtual Bytes
+  next() _OVERRIDE;
+
+  // get n COs; if the remaining number of COs < n, return all;
+  virtual void
+  read(vector<Bytes> &vco, int n) _OVERRIDE;
+
+  // size in terms of number of COs
+  // This is the lazy form of size, i.e. it returns the size cached in this object
+  // but that may not necessarily equal to the actual size kept in file
+  // This is enough if the caller knows for sure that no other thread is changing the
+  // file or the caller does not care about the new size.
+  virtual int
+  size() const _OVERRIDE;
+
+  // this returns the actual size (also update the size cache in this object), but it is more costly, and requires file IO
+  int
+  fSize();
+
+  // the index of the CO to be read
+  int
+  index();
+
+  // set the pos to be the desired CO
+  // return true if success
+  bool
+  seek(int index);
+
+  // reset pos to be zero
+  void
+  rewind();
+
+protected:
+  // write lock should have been grabbed already before the call
+  void
+  prepareWrite();
+
+  // read or write lock should have been grabbed already before the call
+  void
+  checkInit(const string &msg);
+
+  // read lock should have been grabbed already before the call
+  void
+  updateSize();
+
+  #define MAGIC_NUM 0xAAAAAAAA
+
+protected:
+  string m_filename;
+  ifstream m_istream;
+  ofstream m_ostream;
+  Lock m_lock;
+  bool m_writable;
+  bool m_initialized;
+  // capacity in terms of number of COs
+  int m_cap;
+  int m_size;
+  // the index (or seq) of the CO to be read
+  int m_index;
+};
+
+void inline
+writeInt(ostream &out, const int &x)
+{
+  out.write((const char *)&x, sizeof(int));
+}
+
+void inline
+readInt(istream &in, int &x)
+{
+  in.read((char *)&x, sizeof(int));
+}
+
+// write size and then the actual bytes
+// operator << overloading is not used to avoid confusion
+void
+writeBytes(ostream &out, const Bytes &bytes);
+
+// read size and then the actual bytes
+void
+readBytes(istream &in, Bytes &bytes);
+
+#endif
diff --git a/include/object-db.h b/include/object-db.h
index d99eeb6..4ad8504 100644
--- a/include/object-db.h
+++ b/include/object-db.h
@@ -7,6 +7,9 @@
 using namespace std;
 
 struct ObjectDBException : virtual boost::exception, virtual exception { };
+typedef boost::error_info<struct tag_errmsg, std::string> error_info_str;
+
+void throwException(const string &msg) { boost::throw_exception(ObjectDBException() << error_info_str(msg)); }
 
 typedef unsigned char Byte;
 typedef vector<Byte> Bytes;
@@ -32,25 +35,12 @@
 
   // get n COs; if the remaining number of COs < n, return all;
   virtual void
-  read(const vector<Bytes> &vco, int n) = 0;
+  read(vector<Bytes> &vco, int n) = 0;
 
   // size in terms of number of COs
   virtual int
   size() = 0 const;
 
-  // the current index of in terms of COs
-  virtual int
-  pos() = 0 const;
-
-  // set the pos to be desired pos in terms of COs
-  // return true if success
-  virtual bool
-  seek(int pos) = 0;
-
-  // reset pos to be zero
-  virtual void
-  rewind() = 0;
-
 };
 
 #endif