Department of Computer Science and Information Engineering, National Chung Cheng University, Chia-Yi 621, Taiwan. ckting@cs.ccu.edu.tw|Department of Computer Science and Information Engineering, National Chung Cheng University, Chia-Yi 621, Taiwan. ckting@cs.ccu.edu.tw|Department of Computer Science and Information Engineering, National Chung Cheng University, Chia-Yi 621, Taiwan. ckting@cs.ccu.edu.tw