Data base abstraction

Real-world systems modelled by data bases are often quite complex. It is essential that the data base be structured in a way which supports a users abstractions about the real-world system. The “relation” data type is introduced as a structuring primitive for relational data bases The relation data type has similar abstraction properties to the “record” data type of PASCAL. A data base defined via relation data types is structured as a hierarchy of n-ary relations. It is shown that the consistency of this hierarchic structure can be preserved during update operations by two simple rules. A top-down methodology for data base design with relation data types is developed. This methodology minimizes the number of details with which a designer must contend at one time. In particular, the methodology allows the separation of decisions concerning abstract structure from decisions concerning key identification. The separation simplifies both types of decision making for the data base designer.