@book{KobsaWahlster89,
  editor	= {Kobsa, Alfred and Wahlster, Wolfgang},
  year		= {1989},
  title		= {User Models in Dialog Systems},
  pages		= {4--34},
  publisher	= {Springer},
  series	= {Symbolic Computation Series},
  address	= {Berlin Heidelberg New York Tokyo}
}