The safety three-layer framework: a case study

This paper provides a case study to demonstrate the Safety three-Layer Framework (SLF) concept model. The SLF provides a modular Safety Case supported by engineering models and detailed analysis. System-of-Systems (SoS) issues are addressed with the sharing of “need to know” information to negate some of the issues that hinder current SoS Safety Cases. The paper describes a simple worked example which coherently connects the three techniques (modular safety case, engineering models, and detailed analysis) to demonstrate the SLF approach. The case study uses a previously developed and mature example, although not an actual system, implemented by areas of UK Ministry of Defence (MoD) to test safety theories. It explores relationships and interactions between two systems which are part of a representative SoS with Intellectual Property Rights (IPR) and security “need to know” aspects. The study demonstrates a number of features of the SLF such as how a system´s interfaces can be clearly defined internally and externally and how only relevant aspects of the system can be exposed to other suppliers.