Institute of Information Science, Academia Sinica, Taipei 115, Taiwan.|Institute of Information Science, Academia Sinica, Taipei 115, Taiwan.|Institute of Information Science, Academia Sinica, Taipei 115, Taiwan.|Institute of Information Science, Academia Sinica, Taipei 115, Taiwan.|Institute of Information Science, Academia Sinica, Taipei 115, Taiwan.|Institute of Information Science, Academia Sinica, Taipei 115, Taiwan.