A software architecture for complex real-time systems

The increasing use of computer-based control systems in complex applications requires modelling techniques which make it easier to develop and maintain these systems. One promising approach is to use object-orientation. The difficulty is that a traditional object-oriented programming language is most suitable for use in small projects and therefore is not directly scalable to a heterogeneous and distributed environment. Even if the ability to handle distribution is added to such a language, there are features missing which are of importance for a computer-based industrial control system. Examples of missing features include the ability to define and generate object events and the ability to subscribe to large amounts of data in an efficient way. This paper presents an extended object model which is an extension of a traditional object model and provide the means to manage events and subscription. This extended model also includes support for the specification of both client and server interfaces of an object. Relations defined in the client interface can be used to describe relations between objects. These relations can be used to model the real world expressively. As temporal requirements can be described as parts of the interfaces, it is possible to utilize this information in performing a timing analysis of soft services in the system. The paper also describes the evolution of software architectures during recent years and, finally, presents an architecture which supports both hard and soft real-time requirements