G. Sautter, K. Böhm, und D. King. Digital Libraries: Social Media and Community Networks, Seite 161--170. Cham, Springer International Publishing, (2013)
U. Brandes, und T. Willhalm. Proceedings of the symposium on Data Visualisation 2002, Seite 159--ff. Aire-la-Ville, Switzerland, Switzerland, Eurographics Association, (2002)