1. Astrahan, M.M. et al.: System R: Relational Approach to Database Management, ACM Trans. on Database Systems, Vol. 1, No. 2, June 1976. pp. 97–137.
2. Bubenko, J. A.: The Temporal Dimension in Information Processing. Architecture and Models in Database Management, G.M. Nijssen, Ed. North Holland, 1977, pp. 93–118.
3. Chamberlin, D.D. et al: SEQUEL 2: A Unified Approach to Data Definition, Manipulation, and Control, IBM Journal of Research and Development, Nov. 1976. pp. 560–575.
4. Clifford, J., Warren, D.S.: Formal Semantics of Time in Databases. ACM TODS, Vol. 8, No. 2, 1983. pp. 214–254.
5. Date, C. J.: An Introduction to Database Systems, Addison-Wesley Publishing Company, 1981.