1. A. Aiken, J. Widom, and J.M. Hellerstein. Behavior of database production rules: Termination, confluence and observable determinism. In Proc. ACM-SIGMOD, San Diego, pages 59–68. ACM, May 1992.
2. E. Baralis and J. Widom. An algebraic approach to rule analysis in expert database systems. In Proceedings of the International Conference on VLDB, 1994.
3. M. Buchheit, M.A. Jeusfeld, W. Nutt, and M. Staudt. Subsump-tion between queries to object-oriented databases. Information Systems, 19(1):33–54, 1994.
4. A.P. Buchmann, H. Branding, T. Kudrass, and J. Zimmermann. Reach: A real-time active and heterogeneous mediator system. IEEE Bulletin of the TC on Data Engineering, 15(1-4):44–47, December 1992.
5. S. Ceri, P. Pratemali, S. Paraboschi, and L. Tanca. Constraint enforcement through production rules: Putting active databases to work. IEEE Bulletin of the TC on Data Engineering, 15(1-4):10–14, December 1992.