1. School of Software Engineering, Xi’an Jiaotong University, Xi’An, Shaanxi, China
2. Ministry of Education Key Laboratory of Intelligent Networks and Network Security (MOEKLINNS), Xi’an Jiaotong University, Xi’An, Shaanxi, China
3. Department of Computer Science, Drexel University, Philadelphia, PA, USA
4. Department of Information Technology Management, University of Hawaii, Honolulu, HI, USA