B. Weischedel, and E. Huizingh. ICEC '06: Proceedings of the 8th international conference on Electronic commerce, page 463--470. New York, NY, USA, ACM, (2006)
D. Millen, J. Feinberg, and B. Kerr. CHI '06: Proceedings of the SIGCHI conference on Human Factors in computing systems, page 111--120. New York, NY, USA, ACM Press, (2006)
D. Gruhl, R. Guha, D. Liben-Nowell, and A. Tomkins. WWW '04: Proceedings of the 13th international conference on World Wide Web, page 491--501. New York, NY, USA, ACM Press, (2004)