Flexible Object-Oriented Views Using Method Propagation

Object-oriented views play a key role when giving accessing applications a new or restricted perspective on persistent object-oriented data. However, traditional object-oriented view systems only allow for limited changes when it comes to restructuring a database schema and the related persistent objects in a view. We present a new approach for defining object-oriented views that enables view schemas and view objects whose structure is highly flexible with respect to the underlying database structure. Nevertheless we can guarantee complete type-safety of view schemas and a well-defined and consistent behavior when running updates on view objects as well as on underlying database objects. We reach this goal through the concept of method propagation: given that a method of a persistent base class fulfills certain conditions, it can be attached to view classes after its signature is appropriately adjusted. At runtime a method call on a view object is delegated to a corresponding base object and executed there. In the course of this paper we introduce a formal model for objectoriented databases which serves as a basis for defining method propagation conditions. We then present a view language that is derived from our formal approach and highlight the architecture of a prototypical view system.