@incollection{WahlsterKobsa89,
  author	= {Wahlster, Wolfgang and Kobsa, Alfred},
  editor	= {Kobsa, Alfred and Wahlster, Wolfgang},
  year		= {1989},
  title		= {User models in dialog systems},
  booktitle	= {User Models in Dialog Systems},
  pages		= {4--34},
  note		= {(Symbolic Computation Series)},
  publisher	= {Springer},
  address	= {Berlin}
}