C. Ziegler, S. McNee, J. Konstan, and G. Lausen. Proceedings of the 14th International Conference on World Wide Web, page 22--32. New York, NY, USA, ACM, (2005)
K. Badran, and P. Rockett. GECCO '07: Proceedings of the 9th annual conference on
Genetic and evolutionary computation, 2, page 1551--1558. London, ACM Press, (7-11 July 2007)