Interoperability problems-prevention is better than cure

For many years there has been a tendency for very large scale systems to be conceived and built as an amalgamation of a number of smaller systems. Such `systems of systems´ appear to be merely extensions of the normal engineering practice in which systems are made up of a number of sub-systems which can often operate independently to perform a complete function of some sort and so be properly defined as smaller systems in their own right. Given this, why do the large `systems of systems´ or `supersystems´ seem to produce a disproportionate number of problems when compared to their smaller counterparts? The problem in evolving the supersystem is how to integrate the component systems so that they work as a combined whole. The answer clearly lies in achieving interoperability between them, and experience is that this has very rarely been as successful as intended. The purpose of this paper is to discuss the nature of supersystems, to describe interoperability and its role in the development of such systems, and to propose a means for reducing the risk of interoperability problems occurring. The method proposed relies upon the concepts of OSI and recognises the importance and role of the operator as part of the system