The COAST Project: Design and Implementation

. The Complex Object And Schema Transformation (COAST) project focuses on the design and implementation of a schema evolution support system using the versioning concept both at the instance and at the schema level of object-oriented database management systems (OODBMS). The versioning approach to schema evolution offers a high degree of flexibility. In ordinary systems two elements depend heavily on the database schema, and therefore prevent schema changes in many cases: The database which is stored according to the types specified in the schema and the set of application programs on top of the schema which require certain properties from the instances. The basic idea of the versioning mechanism is to keep the old schema and database state as a version to allow continuous operation of existing application programs. This decouples the schema from existing instances and applications, and allows arbitrary schema updates at any time. The main contributions of this paper include the develo...