School of Information, Renmin University of China, Beijing 100872, PR China. wangrsh@amss.ac.cn|School of Information, Renmin University of China, Beijing 100872, PR China. wangrsh@amss.ac.cn|School of Information, Renmin University of China, Beijing 100872, PR China. wangrsh@amss.ac.cn|School of Information, Renmin University of China, Beijing 100872, PR China. wangrsh@amss.ac.cn