Department of Computer Science, Sogang University, Seoul, Korea. shkim@lex.yonsei.ac.kr|Department of Computer Science, Sogang University, Seoul, Korea. shkim@lex.yonsei.ac.kr|Department of Computer Science, Sogang University, Seoul, Korea. shkim@lex.yonsei.ac.kr|Department of Computer Science, Sogang University, Seoul, Korea. shkim@lex.yonsei.ac.kr