The Renaissance Distributed Object System

Object-oriented techniques stress modularity through narrow and rigidly deened interfaces as a way of achieving low coupling between individual software components and high cohesion in the implementation of each component. Unfortunately, in a distributed environment object-oriented interfaces are usually only enforced and usable through language mechanisms or rigid programming conventions. Both of these limitations make it diicult for components in a large-scale distributed environment to interact. This paper discusses a technique that overcomes these limitations and allows for strong interface descriptions that are available at runtime with very small overheads. Our system allows for the dynamic querying of objects for their conformance to a client's requirements speciied as an interface description. We also support the automatic generation of local proxy objects to access remote objects once their conformance is connrmed. The conformance rules we have chosen are more exible than other approaches and allow for a high degree of autonomy between client and server. The approach we use converts interface descriptions into code that can be linked to programs written in various object-oriented and non-object-oriented languages. It diiers from other similar systems in both the conformance checking rules used and in the ability to specify semantic attributes of distributed objects separate from their interfaces. The result is an environment that yields many of the beneets of tightly coupled systems (e.g. strong interfaces and support for static type checking) but maintains many of the beneets of loosely coupled systems (e.g. higher degrees of autonomy, dynamic type checking when necessary, and dynamic operating invocation).