The most important phase in the design of an information system is, in our opinion, the phase which we have given the name Information Analysis (I.A.). During I.A. a conceptual schema is designed which accurately reflects the deep semantic structure of the information which will eventually be used in the information system.
After analyzing the major problems with current information systems, a description is given of how some of these problems may be solved. An essential tool in narrowing the understanding gap between computer specialists on the one side and managers and end-users on the other, is the conceptual schema. The requirements for the concepts in the conceptual schema are discussed and the major candidates for the conceptual schema are briefly evaluated. A gross architecture for the next generation database management systems is presented; essential in this architecture is the conceptual schema, the coextistence of various user mental models and the coexistent use of various manipulation languages as well as the coexistent use of various physical databases on one or more computers. Hence we have given it the name: COEXISTENCE model.
In a schema written in CODASYL DDL 1973, it is syntactically correct to describe an attribute of an entity either by declaring a data item in the record of the entity or by declaring a CODASYL set type in which the record, describing the entity, is a member record. This is considered a major flaw, because extension of a database or integration of two existing databases will then lead to either reprogramming or inconsistency, or both. Examples are described to illustrate situations which occur with a dynamic database. This flaw in the CODASYL DDL 1973 can easily be corrected by requiring that all attributes are represented as a data item in the (logical) schema.
The concept data base is described to serve as a basis to derive data base management system requirements. The main aspects of CODASYL's common data base management languages, DDL and DML will be explained without going to details. The influence of DDL and DML on application programs will be analyzed.
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