The Shell Model - A Method for System Boundary Analysis

The application of analysis methods in systems and safety engineering depends on the available depth of knowledge about a system in the respective lifecycle phases. However, the analysis method chain shows gaps as it should support system analyses during the whole lifecycle of a system. The aim of this paper is to discuss the Shell Model Analysis method, which aims at closing a gap in early system lifecycle phases, like the concept phase. The Shell Model Analysis is a graphical method that splits up a system and groups its parts into concentric shells, built around a selected system part under consideration. A set of rules and guidelines has been defined in order to enable a proper shell build-up. Originally, the method was intended to assist the analysis of electronic system parts, like e.g. an embedded control unit for a braking system, by supporting the definition and analysis of the system’s boundary and its environment only. Meanwhile, it has been extended to also produce results that can be starting points for consecutive analysis methods.