Towards multi-level and modular conceptual schema specifications

The specification of the conceptual schema for a data base application is divided into levels. It is argued that, at the highest level, a direct description of the characteristics of the information kept in a data base and of the constraints governing their existence and transformation of its components characterizes what a particular data base is in a more fundamental way (hence at a higher and more stable level) than the operations that happen to be used for data base manipulation. At a next lower level a specification based on operations, using the encapsulation strategy of abstract data types, is introduced, followed by a specification based on representations used in semantic data models. The discussion includes constraints involving temporal aspects. Modularization is also discussed as another dimension in the specification process, orthogonal to the division into levels.