Hierarchical Safety Cases

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The development of a safety case has become common practice for the certification of systems in many safety-critical domains, but large safety cases still remain difficult to develop, evaluate and maintain. We propose hierarchical safety cases (hicases) as a technique to overcome some of the difficulties that arise in manipulating industrial-size safety arguments. This paper introduces and motivates hicases, lays their formal foundations and relates them to other safety case concepts. Our approach extends the existing Goal Structuring Notation (GSN) with abstraction mechanisms that allow viewing the safety case at different levels of detail.