1. Department of Management Information Systems, Kyonggi University, 154-42 Gwanggyosan-ro, Yeongtong-gu, Suwon-si, Gyeonggi-do 443-760, Republic of Korea
2. Department of Computer & Web Information Engineering, Computer System Institute, Hankyong National University, 327 Jungang-ro, Anseong-si, Gyeonggi-do 456-749, Republic of Korea