B. Pinkerton. Proceedings of the 2nd International World Wide Web, том 18(6) из Online & CDROM review: the international journal of, Medford, NJ, USA, Learned Information, (1994)
R. Baeza-Yates, и C. Castillo. Soft Computing Systems - Design, Management and, стр. 565--572. IOS Press Amsterdam, Berlin, Oxford, Tokyo, Washington, (2002)