College of Computer and Information Sciences, Southwest University, Beibei, Chongqing, China. gxyu@swu.edu.cn.|Department of Computer Science, Hong Kong Baptist University, Hong Kong, Hong Kong. hlzhu@comp.hkbu.edu.hk.|Department of Computer Science, George Mason University, Fairfax, VA, USA. carlotta@cs.gmu.edu.|Department of Computer Science, Hong Kong Baptist University, Hong Kong, Hong Kong. jiming@comp.hkbu.edu.hk.