Time as non-functional requirement in distributed control systems

When designing a distributed control system consisting of heterogeneous components whose properties are usually not well known, it is difficult or even impossible to use an analytical approach to verify the fulfillment of all requirements. In this contribution, it is shown (at the example of different implementation scenarios for a typical control function) that detailed knowledge about the communication system is required to reliably assess and compare different designs of distributed systems with regard to a real-time characteristic. However, automation engineers typically can neither be expected to have such detailed knowledge about the internal details of computing and communication, nor do they have the time to study different design alternatives in detail. This motivates further work of the authors towards better engineering support for the design of distributed automation systems, by providing helpful advice regarding design decisions.