A View Class Mechanism for Object-Oriented Database Systems

Object-oriented database systems generally tend to impose a single, structural view on users. This paper proposes a new mechanism, called view class, which realizes various views for object-oriented databases. The view class, created by query primitives and additional methods, enables information hiding as well as the ability to provide a join view or a group view. In addition to the language for view class definition and manipulation, an implementation scheme is given. The scheme makes it possible to hide methods (called method projection), or to determine a method uniquely where an instance object can belong to several classes. A view anomaly problem, which occurs due to introduction of the method projection and its solution, are presented. Also shown are some problems which occur when a database is updated through a view. They are solved by making direct reference to source objects through view classes, and by storing update semantics in the form of methods.