S. Charfi, E. Dubois, and R. Bastide. Task Models and Diagrams for User Interface Design, volume 4849 of Lecture Notes in Computer Science, Springer Berlin Heidelberg, (2007)
D. Porta, and J. Conrad. Proceedings of the 13th international conference on intelligent user interfaces, page 393--396. New York, NY, USA, ACM, (2008)