Department of Computer Science and Information Engineering, National Cheng Kung University, Tainan, Taiwan. jchiang@mail.ncku.edu.tw|Department of Computer Science and Information Engineering, National Cheng Kung University, Tainan, Taiwan. jchiang@mail.ncku.edu.tw|Department of Computer Science and Information Engineering, National Cheng Kung University, Tainan, Taiwan. jchiang@mail.ncku.edu.tw|Department of Computer Science and Information Engineering, National Cheng Kung University, Tainan, Taiwan. jchiang@mail.ncku.edu.tw