1. Kerschberg, L., Klug, A. and Tsichritzis, D. — "A taxonomy of data models" — Proc. of the Very Large Data Bases Conference (1976).
2. Reisner, P. — "Use of psychological experimentation as an aid to development of a query language", — IEEE Transactions on Software Engineering, SE-3,3 (1977) 218–229.
3. Zloof, M.M. — "Query by example" — Proc. of National Computer Conference (1975).
4. Mc Donald, N. and Stonebraker, M. — "Cupid: the friendly query language" — Proc. of ACM Pacific Conference (1975).
5. Date, C.J. — "An introduction to data-base systems" — Addison-Wesley (1975).