Updatable Views in Object-Oriented Databases

Object-oriented database systems (ooDBMSs) are supposed to offer at least the functionality available in commercial relational DBMSs of today. One important consequence of this is that they have to provide a separation of the global (conceptual) database schema from the external schema (“subschema”) of a particular task. Views are a mechanism to realize this data independence. In addition, they also support multiple levels of detail, security and authorization, and interoperability in a heterogeneous environment. In a relational DBMS, views are defined by queries. However, they can not be freely updated. We describe concepts of an object model and query language that are necessary for object view definitions. We show that updating object views is much more feasible than in the case of relational views. The key property of a query language leading to this result is object preserving operator semantics. That is, in contrast to many previous object algebras, query results are sets of existing objects instead of data tuples or new objects. Consequently, we have to solve the classification problem: where to include the view in the type and class lattices.