J. Kreutel. Proceedings of the 8th SIGdial Workshop on Discourse and Dialogue, page 235–238. Association for Computational Linguistics (ACL), (September 2007)
F. Radeke, and P. Forbrig. Proceedings of the 6th international conference on Task models and diagrams for user interface design, page 184--197. Berlin/Heidelberg, Springer-Verlag, (2007)