Various proposals have been made to extend object-oriented languages and database systems with roles because they allow to weaken strict typing concepts and therefore can provide mechanisms for an object to change its type during its lifetime. This so-called object migration is not the only advantage offered by a suitable role model. This paper studies the possibilities to use roles for a general change management system that also includes support for schema evolution. OPAQUE, as the selected role model, can be extended with schema update mechanisms in a surprisingly clean and straightforward way including the concepts of versions and views as well.

Object-oriented database systems (OODBMS) offer powerful modeling concepts as required by advanced application domains like CAD/CAM/CAE or office automation. Typical applications have to handle large and complex structured objects which frequently change their value and their structure. As the structure is described in the schema of the database, support for schema evolution is a highly required feature. Therefore, a set of schema update primitives must be provided which can be used to perform the required changes, even in the presence of populated databases and running applications. In this paper, we use the versioning approach to schema evolution to support schema updates as a complex design task. The presented propagation mechanism is based on conversion functions that map objects between different types and can be used to support schema evolution and schema integration.