T. Primo, and R. Vicari. Advanced Learning Technologies (ICALT), 2011 11th IEEE International Conference on, page 598-599. IEEE Computer Society, (2011)
P. Bra, D. Smits, and N. Stash. Innovative Approaches for Learning and Knowledge Sharing, volume 4227 of Lecture Notes in Computer Science, Springer Berlin Heidelberg, (2006)