Department of Computer Science and Information Engineering, National Cheng Kung University, Tainan 701, Taiwan, ROC. jchiang@mail.ncku.edu.tw|Department of Computer Science and Information Engineering, National Cheng Kung University, Tainan 701, Taiwan, ROC. jchiang@mail.ncku.edu.tw|Department of Computer Science and Information Engineering, National Cheng Kung University, Tainan 701, Taiwan, ROC. jchiang@mail.ncku.edu.tw