Database schema evolution using EVER diagrams

We present an approach to schema evolution through changes to the ER diagram representing the schema of a database. In order to facilitate changes to the ER schema we enhance the graphical constructs used in ER diagrams, and develop EVER, an Evolutionary ER diagram for specifying the derivation relationships between schema versions, relationships among attributes, and the conditions for maintaining consistent views of programs. In this paper, we demonstrate the mapping of the EVER diagram into an underlying database and the construction of database views for schema versions. Through the reconstruction of views after database reorganization, changes to an ER diagram can be made transparent to the application programs while all objects in the database remain accessible to the application programs. The EVER system can serve as a front-end for object-oriented databases.