1. The Hong Kong Polytechnic University,Department of Computing,Hong Kong,P. R. China
2. City University of Hong Kong,Department of Computer Science,Hong Kong,P. R. China
3. Temple University,Department of Computer and Information Sciences,Philadelphia,USA
4. Guangdong University of Technology,Guangzhou,P. R. China,510006
5. Dalian University of Technology,School of Software,Dalian,P. R. China,116621
6. Sichuan University,College of Computer Science,Chengdu,P. R. China,610065