F.  Giannotti, Pedreschi, D., and Zaniolo, C., ?Semantics and Expressive Power of Nondeterministic Constructs in Deductive Databases?, J. Comput. Syst. Sci., vol. 62, pp. 15-42, 2001.

F.  Giannotti, Greco, S., Saccà, D., and Zaniolo, C., ?Programming with Non-Determinism in Deductive Databases?, Ann. Math. Artif. Intell., vol. 19, pp. 97-125, 1997.

D.  Pedreschi and Zaniolo, C., ?Logic in Databases, International Workshop LID'96, San Miniato, Italy, July 1-2, 1996, Proceedings?, Lecture Notes in Computer Science, vol. 1154. Springer, 1996.

L.  Corciulo, Giannotti, F., Pedreschi, D., and Zaniolo, C., ?Expressive Power of Non-Deterministic Operators for Logic-based Languages?, in Workshop on Deductive Databases and Logic Programming, 1994, pp. 27-40.

F.  Giannotti, Pedreschi, D., Saccà, D., and Zaniolo, C., ?Non-Determinism in Deductive Databases?, in DOOD, 1991, pp. 129-146.