1. S. Abiteboul and R. Hull, ?IFO: A formal semantic database model,?ACM Trans. Database Syst. vol. 12, no. 3, pp. 525?565, 1987.
2. P. Atzeni and D. S. Parker, ?Formal properties of net-based knowledge representation schemes,?Data Knowledge Eng. vol. 3, pp. 137?147, 1988.
3. T. W. Finin and D. Silverman, ?Interactive classification as a knowledge acquisition tool,? inExpert Database Systems?Proceedings From the 1st International Workshop edited by L. Kerschberg, Benjamin/Cummings: Menlo Park, CA, pp. 79?90, 1986.
4. L. Delcambre and K. Davis, ?Automatic validation of object-oriented database structures,? in5th Int. Conf. Data Eng., Los Angeles, CA, 1989, pp. 2?9.
5. C. Lécluse and P. Richard, ?Modeling complex structures in object-oriented databases,? inProc. 8th ACM SIGACT-SIGMOD-SIGART Symp. Principles of Database-Systems, Philadelphia, PA, 1989, pp. 360?367.