Architecture for Open Distributed Software Systems

Distributed applications consist of discrete software components which are spread across multiple systems. The interaction between these components constitutes distributed processing. If the discrete components are capable of exhibiting " openness " , then the interaction between them can be characterized as open distributed processing. In an ideal open distributed system, it should be possible for distributed applications developed in different environments to interact. This can be achieved if distributed environments conform to a common conceptual model or architecture. This chapter describes a common conceptual framework for the design of distributed systems, which is gaining a wide degree of acceptance within the distributed systems research community. This is the basis for the standardization of Reference Model for Open Distributed Processing (RM-ODP). The chapter is divided into five parts. Part-1 is an introduction to the architecture for open distributed systems. A set of five abstraction levels-enterprise viewpoint, information viewpoint, computational viewpoint, engineering viewpoint, and technology viewpoint, are identified in RM-ODP for the specification of distributed software systems. While all the viewpoints are relevant to the design of distributed systems, the computation and engineering models are the ones that bear most directly on the design and implementation of distributed systems. From a distributed software engineering point of view, the computational and engineering viewpoints are the most important; they reflect the software structure of the distributed application most closely. In this chapter, we concentrate on 2 the computational and engineering viewpoints in Part-2 and Part-3 respectively. Part-4 is an illustration of the application of ODP architectural concepts in a simple client-server scenario. Conclusions are drawn in Part-5. Today's distributed systems are complex structures, composed of many types of hardware and software components. In some systems, components are developed separately by different implementors, and then combined together resulting in a heterogeneous system. Well known examples of such systems, which fall within the scope of the distributed systems architecture addressed in this chapter, include telecommunication systems (advanced intelligent networks), computer communication networks (internet), automated manufacturing systems, office automation systems, client-server systems (banking and airline reservation systems), etc. In order to reason about such systems, it is necessary to develop appropriate concepts. These concepts may vary according to the point of view from which the system is being considered. For example, from the end user's point of view, the system will be described in terms of user objectives and requirements. From the application designer's point of …