A methodological approach to the requirement specification of embedded systems

A systematic development process for describing requirement specifications of embedded safety relevant systems is presented. The procedure resembles the V model, widely used in practice, according to which the software production is divided into different steps. Concrete guidelines are given that lead to structured requirement specifications of embedded cyclic systems for which real time conditions and safety critical characteristics play a role. When describing the system, it is divided into the whole system (hardware and software) and the controller (only software). By doing so, a clear division is gained between the values of the system and the values which are available to the controller. On this basis hardware failures arising in the whole system can be described and considered by means of the control software. Different formal, semi formal, and graphical notations are suggested which can be used in combination in order to describe various aspects of a system. The different notations and the various requirement types are classified so that a simple description and analysis of requirements is possible. Formal notations are not urgently necessary for being able to carry out the development steps suggested here. However, due to their precision and their automation potential the formal notations are strongly recommended especially for safety critical software.