diff --git a/src/file-state.h b/src/file-state.h
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--- /dev/null
+++ b/src/file-state.h
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+/* -*- Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil -*- */
+/*
+ * Copyright (c) 2012-2013 University of California, Los Angeles
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation;
+ *
+ * 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
+ *
+ * Author: Alexander Afanasyev <alexander.afanasyev@ucla.edu>
+ *	   Zhenkai Zhu <zhenkai@cs.ucla.edu>
+ */
+
+#ifndef FILE_STATE_H
+#define FILE_STATE_H
+
+#include "file-item.pb.h"
+#include "hash-helper.h"
+
+#include <boost/tuple/tuple.hpp>
+#include <boost/exception/all.hpp>
+
+#include <list>
+
+typedef std::list<FileItem> FileItems;
+typedef boost::shared_ptr<FileItem>  FileItemPtr;
+typedef boost::shared_ptr<FileItems> FileItemsPtr;
+
+
+class FileState
+{
+public:
+  virtual FileItemPtr
+  LookupFile (const std::string &filename) = 0;
+
+  virtual FileItemsPtr
+  LookupFilesForHash (const Hash &hash) = 0;
+
+  virtual FileItemsPtr
+  LookupFilesInFolder (const std::string &folder) = 0;
+
+  virtual FileItemsPtr
+  LookupFilesInFolderRecursively (const std::string &folder) = 0;
+};
+
+namespace Error {
+struct FileState : virtual boost::exception, virtual std::exception { };
+}
+
+
+#endif // ACTION_LOG_H