A Global Perspective of Schema Modification Management for Object-Oriented Databases

Schema Modification Management (SMM) is concerned about how schema changes should affect the object base in order to make database objects be compatible with specifications after change. However, a particular problem with existing SMM approaches is the lack of concern for schema-level changes (which may involve multiple classes), or semantic dependencies which applies between non-consecutive versions of the schema. The presented approach adopts a schema versioning approach to SMM (allowing multiple schema versions to coexist), and promotes a global perspective of change management: A powerful means is provided for specifying the presence and maintenance of arbitrary semantic relationships between classes and properties as defined for any schema version in the derivation hierarchy. The fundamental assumption is that semantic dependencies between schema versions do not only follows the derivation relationship, but may go in any directions. To ensure the database behaves consistently as regarded within any schema version context, it is essential that all semantic dependencies are maintained. The approach is able to handle schema version derivations in arbitrary directions, including complex modifications to the class hierarchy, and in accordance with the inherently unpredictable nature of change.