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)
R. Keller, S. Wolfe, J. Chen, J. Rabinowitz, and N. Mathe. Selected papers from the sixth international conference on World Wide Web, page 1103--1114. Essex, UK, Elsevier Science Publishers Ltd., (1997)