V. Gómez, A. Kaltenbrunner, and V. López. WWW '08: Proceeding of the 17th international conference on World Wide Web, page 645--654. New York, NY, USA, ACM, (2008)
U. Brandes, P. Kenis, J. Lerner, and D. van Raaij. WWW '09: Proceedings of the 18th international conference on World wide web, page 731--740. New York, NY, USA, ACM, (2009)
R. Klamma, and C. Haasler. Proceedings of I-KNOW '08 and I-MEDIA '08, page 276--279. Know-Center, Graz, Journal of Universal Computer Science, (September 2008)