An Approach For Schema Evolution in ODMG Databases

Schema evolution is the process of applying changes to a schema in a consistent way and propagating these changes to the instances while the database is in operation. However, when a database is shared by many users, updates to the database schema are always difficult. To overcome this problem, in this paper we propose a version mechanism for schema evolution in ODMG databases that preserves old schemas for continued support of existing programs running on the shared database when schema changes are produced. Our approach uses external schema definition techniques and is based on the fact that if a schema change is requested on an external schema, rather than modifying the schema, a new schema, which reflects the semantics of the schema change, is defined.