P. Koehn, F. Och, and D. Marcu. Proceedings of the 2003 Conference of the North American Chapter of the Association for Computational Linguistics on Human Language Technology-Volume 1, page 48--54. Association for Computational Linguistics, (2003)
M. Zhang, Y. Liu, H. Luan, and M. Sun. Proceedings of the 55th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers), 1, page 1959--1970. (2017)