1. School of Software, Dalian, Liaoning, China
2. Department of Computer Science, City University of Hong Kong, Hong Kong
3. International School of Information Science and Engineering, Key Laboratory for Ubiquitous Network and Service Software of Liaoning Province, Dalian University of Technology, Dalian, Liaoning, China
4. Department of Computer Science, Sichuan University, Chengdu, Sichuan, China
5. School of Cyber Science and Engineering, Huazhong University of Science and Technology, Wuhan, Hubei, China