T. Scheffler, R. Roller, and N. Reithinger. Proceedings of the 6th IJCAI Workshop on Knowledge and Reasoning in Practical Dialogue Systems, Pasadena, CA, USA, page 93-98. (2009)
P. Ehlen, M. Johnston, and G. Vasireddy. Proceedings of ICSLP---Interspeech 2002: 7th International Conference on Spoken Language Processing, Denver, CO, USA, page 2557-2560. (2002)