B. G. 1, chapter in Encyclopedia of Portal Technology and Applications, page 522-526. Hershey, PA, Information Science Reference, USA, (2007)http://lccn.loc.gov/2007007262.
J. Gemmell, A. Shepitsen, B. Mobasher, and R. Burke. Proceedings of the 10th international conference on Data Warehousing and Knowledge Discovery, page 196--205. Berlin, Heidelberg, Springer-Verlag, (2008)