L. Bollen, A. Harrer, H. Hoppe, и W. van Joolingen. The 7th IEEE International Conference on Advanced Learning Technologies ICALT 2007, стр. 15-17. Los Alamitos, CA., IEEE Computer Society, (2007)
X. Shuai, Z. Jiang, X. Liu, и J. Bollen. Proceedings of the 13th ACM/IEEE-CS Joint Conference on Digital Libraries, стр. 25--28. New York, NY, USA, ACM, (2013)