1. P. Loucopoulos and R. Zicari, editors. Conceptual Modeling, Databases, and CASE: An Integrated View of Information Systems Development. John Wiley & Sons, Inc., 1992.
2. R.J. Wieringa. Three Roles of Conceptual Models in Information System Design and Use. In E. Falkenberg and P. Lindgreen, editors, Information System Concepts: An In-Depth Analysis, Proc. IFIP WG8.1 Working Conference, Namur (Belgium), pages 31–51. North-Holland, Amsterdam, 1989.
3. H.-D. Ehrich, G. Denker and A. Sernadas. Constructing Systems as Object Communities. In M.-C. Gaudel and J.-P. Jouannaud, editors, Proc. TAPSOFT'93: Theory and Practice of Software Development, pages 453–467. Springer LNCS 668, 1993.
4. S. Conrad, M. Gogolla and R. Herzig, TROLL light: A Core Language for Specifying Objects. Informatik-Bericht 92-02, Technische Universität Braunschweig, 1992.
5. A. Sernadas, C. Sernadas, and H.-D. Ehrich. Object-Oriented Specification of Databases: An Algebraic Approach. In P.M. Stocker and W. Kent. editors, Proc. 13th Int. Conf. on Very Large Data Bases VLDB, pages 107–116. Morgan-Kaufmann, 1987.