A multi-level relational system
John Mylopoulos, Stewart A. Schuster, D. Tsichritzis · 1975
A relation can be conceptually viewed as a table of data. The table's heading defines the relation's name, the column headings are the attribute names, and each row corresponds to an n-tuple of data values describing a single entity. The set of values which can be used in a column is called a domain. A relational data base is composed of a set of time varying relations inter-related through common domains.