@inproceedings{stumme99numerical,
  author = {Stumme, G. and Wolff, K. E.},
  title = {Numerical Aspects in the Data Model of Conceptual Information Systems},
  booktitle = {Advances in Database Technologies. Proc. Intl. Workshop on Data Warehousing and},
  publisher = {Springer},
  year = {1999},
  volume = {1552},
  pages = {117-128},
  url = {http://www.kde.cs.uni-kassel.de/stumme/papers/1998/ER98.pdf}
}

@inproceedings{Stumme1999acquiring,
  author = {Stumme, Gerd},
  title = {Acquiring Expert Knowledge for the Design of Conceptual Information Systems},
  booktitle = {Knowledge Acquisition, Modeling, and Management. Proc. 11th European},
  publisher = {Springer},
  year = {1999},
  volume = {1621},
  pages = {275-290},
  url = {http://www.kde.cs.uni-kassel.de/stumme/papers/1999/P1997-EKAW99.pdf}
}

@inproceedings{stumme99dual,
  author = {Stumme, Gerd},
  title = {Dual Retrieval in Conceptual Information Systems},
  booktitle = {Datenbanksysteme in Büro, Technik und Wissenschaft. Proc. BTW'99},
  year = {1999},
  pages = {328-342},
  url = {http://www.kde.cs.uni-kassel.de/stumme/papers/1999/P2021-BTW99.pdf}
}