1. Central University of Finance and Economics, Beijing, China
2. College of Computer Science and Technology, Huazhong University of Science and Technology (HUST), Wuhan, China
3. Key Laboratory of Intelligent Education Technology and Application of Zhejiang Province, Zhejiang Normal University, Jinhua, China
4. Department of Computer Science, University of Illinois, Chicago, USA
5. Department of Computer Science, University of York, U.K.