1. School of Computer Science and Technology, Xi'an Jiaotong University, Xi'an, China
2. Department of Computer Science, The University of Manchester, Manchester, United Kingdom
3. National University of Singapore, Singapore, Singapore
4. School of Computer Science, Hangzhou Dianzi University, Hangzhou, China
5. National Engineering Lab for Big Data Analytics, Xi'an Jiaotong University, Xi'an, China