StratOSphere: unification of code, data, location, scope, and mobility

The StratOSphere system provides a framework for distributed objects written in Java, unifying mobile code and distributed programming systems by providing the basic entities: relocatable instances and methods, persistent repositories, and mobile execution state. Each StratOSphere host provides a repository to store object instances and methods in a persistent manner The repository is partitioned among different hosts, to distribute the storage of objects, and to provide different implementations of an object specification among particular hosts. Client applications visit relevant repositories to acquire specialized behavior from methods stored within the repository. At run-time these entities can be accessed and dispatched, providing a means of invoking an operation in a dynamic fashion, while still ensuring type safety and correctness. In addition to unifying externally-defined methods with compiled objects, and providing location transparency through mobility, StratOSphere further unifies different versions of an object, permitting successive implementations to coexist within the system. We discuss the architecture and implementation of StratOSphere, describing how the goals of unifying different aspects of distributed computing have influenced its design.