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.
['John Mylopoulos', 'Stewart A. Schuster', 'Dennis Tsichritzis']
A multi-level relational system