R. Baeza-Yates, и C. Castillo. Soft Computing Systems - Design, Management and, стр. 565--572. IOS Press Amsterdam, Berlin, Oxford, Tokyo, Washington, (2002)
S. Dumais, E. Cutrell, J. Cadiz, G. Jancke, R. Sarin, и D. Robbins. Proc. of the 26th annual international ACM SIGIR conference on Researchand development in informaion retrieval, стр. 72 - 79. Torontoand Canada, ACM Press New Yorkand NYand USA, (2003)