An entity-relationship approach to schema evolution

A dynamically evolving information system supports changes to its database schema in order to facilitate the needs of new application programs. This paper presents an approach to schema evolution through changes to the entity-relationship schema of a database. This approach has the advantage of being closer to the designer's perception of data, rather than to the logical database schema which describes how data are stored in the database. The underlying database structure is re-organized, if necessary, to accommodate new data without the changes affecting existing objects. In this way and through the construction of views, modifications of existing programs are avoided while all objects in the database are accessible to all application programs, both new and old. Thus, the invariance of the programs' interface is preserved by the views