Department of Computer Science and Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan. wujs@mail.cse.nsysu.edu|Department of Computer Science and Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan. wujs@mail.cse.nsysu.edu|Department of Computer Science and Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan. wujs@mail.cse.nsysu.edu|Department of Computer Science and Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan. wujs@mail.cse.nsysu.edu