Database Schema Evolution through the Specification and Maintenance of Changes on Entities and Relationships

Liu, Chien-Tsai; Chrysanthis, Panos K.; Chang, Shi-Kuo
Liu, C
Chrysanthis, P
Chang, S
Proc. 13th Int. Conf. on Entity-Relationship Approach (ER'94), LNCS 881:132-149, December 1994
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A flexible database system needs to support changes to its
schema in order to facilitate the requirements of new applications
and to support interoperability within a multidatabase system. In this
paper, we present an approach to schema evolution through changes to the
EntityRelationship (ER) schema of a database. 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. Algorithms are presented for mapping
the EVER diagram into the underlying database and constructing 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.