Simulation Driven Development - Validation of requirements in the early design stages of complex systems - the example of the German Toll System

Looking at the end-to-end processing, typical software-intensive systems are built as a system-of-systems where each sub-system specializes according to both the business and technology perspective. One challenge is the integration of all systems into a single system – crossing technological and organizational boundaries as well as functional domains. To facilitate the successful integration we propose the use of simulation models in parallel to the existing software engineering procedures. As an example we look at the German tolling system for heavy goods vehicles (HGVs) – a liability-critical system consisting of some 60 sub-systems including a fleet of more than 1 000 000 onboard units deployed in the HGVs. Since its start in 2005 the system regularly undergoes changes and updates. To mitigate the associated costs and risks we developed a microscopic discrete event simulation (DES) model of the tolling system and use it to support both the design of planned changes and the monitoring of the day-to-day operations. The model includes the dynamic aspects of the tolling system and HGVs interacting with the system. In the article we discuss the use of realistic simulation models as part of the system design process. Since simulations are heavily used by the design process it is called Simulation Driven Development (SDD).