1. School of Computer Engineering, Chengdu Technological University, Chengdu, China
2. School of Software Engineering, Chengdu University of Information Technology, Chengdu, China
3. School of Software, Sichuan Vocational College of Information Technology, Guangyuan, China
4. Faculty of Informatics, Eötvös Loránd University, Budapest, Hungary
5. The Research and Development Department, HAN Networks Corporation Limited, Beijing, China