1. School of Computer Science and Technology, Soochow University, Suzhou, China
2. Department of Computer and Information of Science and Engineering, University of Florida, Gainesville, FL, USA
3. Department of Computer Science, University College London, London, U.K.
4. State Key Laboratory for Novel Software Technology, Nanjing University, Nanjing, China
5. Department of Informatics, University of Oslo, Oslo, Norway
6. College of Computing, Georgia Institute of Technology, Atlanta, GA, USA