@misc{Kees1997,
  author    = {A. Kees},
  title     = {Das Aachener PPS-Modell},
  series = {Vorlesung Diplomstudiengang Wirtschaftsinformatik, Westf{\"a}lische Wilhelms-Universit{\"a}t M{\"u}nster, M{\"u}nster, 09.06.1997},
  year      = {1997},
  language  = {de}
}