View programming for decentralized development of OO programs

There has been a lot of interest recently in the problem of building object-oriented applications by somehow combining other application fragments that provide their own overlapping definitions or expectations of the same domain objects. We propose an approach based on the split objects model of prototype languages whereby an application object is represented by a varying set of instances- - called views- that implement different parts of its domain behavior but that delegate its core functionalities to a core instance: an object's response to a message depends on the views currently attached to its core instance. Our approach is not purely prototype-based in the sense that core instances and views are members of classes. Further, we recognize that the behavior inherent in views (classes) is often an adaptation of a generic behavior to the domain object at hand, and define viewpoints as parameterized class-like algebraic structures to embody such a generic behavior. In this paper, we first describe view programming from the perspective of the developer. Next, we sketch a semi-formal model of view programming, and describe the steps needed to implement it in a class-based statically typed language, for instance, C++. Third, we look at the challenges and opportunities provided by view programming to support safe, robust, and efficient distributed applications.