Maintaining Database Consistency in the Presence of Schema Evolution: An Evolutionary Approach based on Versions of Schema

With rapid advances in computer network technology and the increasing interest in global information sharing, grows the need for facilities that can effectively maintain the database consistency and program compatibility as the schema evolves. In this paper, we present a general framework based on versions of schema for supporting seamless schema evolution in large-scale object-oriented software systems. We argue that the effectiveness of using the schema version model to materialize schema evolution relies not only on the management of version derivation of schema, but also on the ability to maintain consistency of the database instances with the new schema versions, and the flexibility of sharing instance access scopes among versions of schema. Semantics of schema versioning is studied with the objective to facilitate instance adaptation and program compatibility in the presence of schema updates. A number of options for sharing of instance access scopes among versions of a schema is..