M. Pennacchiotti, and A. Popescu. Proceedings of the 17th ACM SIGKDD International Conference on Knowledge Discovery and Data Mining, page 430--438. New York, NY, USA, ACM, (2011)
T. Sakaki, M. Okazaki, and Y. Matsuo. Proceedings of the 19th International Conference on World Wide Web, page 851--860. New York, NY, USA, ACM, (2010)