1. G. Ausiello, C. Batini, M. Moscarini: ‘Conceptual relations between databases transformed under join and projection's in: Proc. Symp. Math. Found. of Comp. Sc., 9, 1980, pp. 123–136
2. P. Atzeni, G. Aussiello, C. Batini, M. Moscarini: ‘Inclusion and equivalence between relational database schemes', in: Theoretical Computer Science, 19, 1982, pp. 267–285
3. P. Atzeni, D.S. Parker: ‘Assumptions in relational database theory', in: ACM Symp. on Princ. of Database Systems, 1, 1982, pp. 1–9
4. A.V. Aho, Y. Sagiv, J.D. Ullman: ‘Equivalences among relational expressions', in: SIAM Journ. of Computing, 8, 1979, pp. 218–246
5. A.V. Aho, J.D. Ullman: ‘Universality of data retrieval languages', in: ACM Symp. on Princ. of Programming Languages, 6, 1979, pp. 110–117