M. Boley, T. Horváth, A. Poigné, and S. Wrobel. PKDD 2007: Proceedings of the 11th European conference on Principles and Practice of Knowledge Discovery in Databases, page 382--389. Berlin, Heidelberg, Springer-Verlag, (2007)
S. Brin, R. Motwani, and C. Silverstein. SIGMOD '97: Proceedings of the 1997 ACM SIGMOD international conference on Management of data, page 265--276. New York, NY, USA, ACM, (1997)