Formal semantics for database schemas (Q1124390)

\textit{P. Atzeni} and \textit{D. S. Parker} [Formal properties of net-based knowledge representation schemes. Proc. 2nd IEEE Conf. Data Engineering, 700-706 (1986)] formulated a system of axioms for the concept of a database schema, based on the ``is-a'' and the disjointness relationships between types. This paper investigates the algebraic properties of this model and of some refinements of it. This approach yields as an important by-product a methodology for designing database schemas which are free of inconsistency and redundancy. Some concrete and typical examples lead to a remarkable clarity in the presentation.