The Many Faces of Safety Cases

This paper discusses the input documents and project decisions that are important when developing a safety case. The discussion is based on interviews with seventeen companies - all engaged in building safety cases for commercial products. The majority of the companies are Norwegian and Swedish. However, we have also interviewed companies from Denmark, UK, USA and Turkey. We discuss issues such as when in the project to start developing a safety case, what are the important inputs needed, and what are the roles of the required standards. Some issues will not be included - e.g. AI systems. The main reason for this is that none of the companies we interviewed developed AI systems.

We also discuss important issues such as the purpose of the safety case, safety case maintenance and the role of reuse when developing a safety case. We will also discuss the relationships between safety case and trust case and how a safety case can be used in communication and to build trust in a system. Our further work will focus on two important areas - traceability between the system and safety case, which is important in order to keep the safety case up to date during system changes - and the possibility of expanding the "case" idea to bridge the communication gap between software developers and customers or users.

Keywords: Safety case, Confidence, Trust, Maintenance.

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