@book{Lang-etal91,
  author	= {Lang, Ewald and Carstensen, Kai-Uwe and Simmons, Geoffrey},
  year		= {1991},
  title		= {Modelling spatial knowledge on a linguistic basis: theory -- prototype -- integration},
  series	= {Lecture Notes in Artificial Intelligence},
  number	= {481},
  publisher	= {Springer},
  address	= {Berlin, Heidelberg}
}