Y. Ahn, S. Han, H. Kwak, S. Moon, and H. Jeong. Proceedings of the 16th International Conference on World Wide Web, page 835--844. New York, NY, USA, ACM, (2007)
A. Brew, D. Greene, and P. Cunningham. Proceedings of the 19th European Conference on Artificial Intelligence, volume 215 of Frontiers in Artificial Intelligence and Applications, page 145--150. Amsterdam, The Netherlands, The Netherlands, IOS Press, (2010)