1. Key Laboratory of Data Engineering and Knowledge Engineering, Renmin University of China, 12471 Beijing, Beijing, China, (e-mail: zhangfeng.thu.hpc@gmail.com)
2. Key Laboratory of Data Engineering and Knowledge Engineering, Renmin University of China, 12471 Beijing, Beijing, China, (e-mail: liuyn1999@gmail.com)
3. Key Laboratory of Data Engineering and Knowledge Engineering, Renmin University of China, 12471 Beijing, Beijing, China, (e-mail: whitycatty@gmail.com)
4. Computer Science, Beijing University of Posts and Telecommunications, 12472 Beijing, Beijing, China, 100088 (e-mail: albertyang33@gmail.com)
5. Department of Computer Science & Technology, Tsinghua University, Beijing, Beijing, China, 100084 (e-mail: zhaijidong@gmail.com)
6. Database Systems and Information Management Group (DIMA), Technische Universitt Berlin, 26524 Berlin, Berlin, Germany, (e-mail: shuhao.zhang@tu-berlin.de)
7. Computer Science, National University of Singapore, 37580 Singapore, Singapore, Singapore, 119260 (e-mail: hebs@comp.nus.edu.sg)
8. Department of Information Management, Peking University, 12465 Beijing, Beijing, China, (e-mail: linjz@pku.edu.cn)
9. School of Information, Renmin University of China, Beijing, Beijing, China, (e-mail: zhangxiao@ruc.edu.cn)
10. School of Information, Renmin University of China, Beijing, Beijing, China, (e-mail: duyong@ruc.edu.cn)