An Integrated Approach to Schema Evolution for Object Databases

This paper deals with the possibility to evolve the schema in an object database management system (ODBMS) by maintaining both the structural consistency of the database and behavioral consistency of applications defined against the schema. The schema evolution model presented in this paper uses both an adaptational approach where the schema and the underlying database are transformed respectively by means of schema update primitives and conversion functions, and a schema versioning approach where new schema versions are created along with the associated databases. The main contribution of this paper is based on the integration of the two approaches in the O 2 object database with the goal of minimizing the overhead of the system. We therefore categorized the set of available schema update primitives into schema extending, and schema modifying primitives, whereby only the latter might require the schema versioning approach as a consequence of applications being corrupted by the schema change. To our knowledge, this s the first time when both approaches have been integrated into a general schema evolution odel.