Types and their management in open distributed systems

Open distributed processing aims to support cooperation within and between large-scale heterogeneous and autonomous computing environments. An inherent issue in such environments is enabling the interoperation of objects whose interfaces have been defined in different type models. In this paper, we present a type management system which provides a means for representing, storing, retrieving and translating types, and for expressing and evaluating relationships between types in a heterogeneous distributed computing environment. This system allows multiple type languages and models, and can relate types expressed in different ones. The type management system is designed to support the instantiation and dynamic binding of objects, run-time type checking of object interactions, and the discovery of new resources (e.g. services) within the system. Current approaches to interface definition in distributed systems are mainly based on the use of a single interface definition language (IDL). While this provides a level of common agreement about the types of system interfaces, the type models of existing IDLs are not rich enough to model either the overall architecture of a system or the behaviour of objects. We illustrate this by briefly describing some aspects of an enhanced type model with the emphasis on the model's impact on the design of the type management system.