Safety Case Composition Using Contracts - Refinements based on Feedback from an Industrial Case Study

Abstract

Modular safety cases provide a means of organising large and/or complex safety cases into separate but interrelated component modules of argument and evidence. Safety case ‘contracts’ can be used to record the interdependencies that exist between safety case modules — e.g. to show how the claims of one module support the arguments of another. A number of techniques for structuring and describing modular safety cases using the Goal Structuring Notation were defined by Kelly in (Kelly 2001). The Industrial Avionics Working Group, (IAWG) has been using these techniques as part of a substantial industrial case study being funded by the UK Ministry of Defence. Based on this experience, and a number of issues encountered, modifications to the original approach have been defined. This paper presents some of these experiences of the IAWG in using’ modular’ GSN — in particular, those relating to capturing and recording safety case contracts — and proposes an enhanced approach.

representing the Industrial Avionics Working Group