Abstract
Assurance cases are documented body of evidence that provide valid and convincing argument that the system is adequately dependable in a given application and an environment. Assurance cases are widely required as a regulation for safety-critical systems in EU. There have been several graphical notations for assurance cases. GSN (Goal Structuring Notation) and CAE (Claim, Argument, Evidence) are such two notations. However, these notations have not been defined in a formal way. This paper presents a formal definition of GSN and its pattern extensions. We take the framework of functional programming language as the basis of our study. The implementation has been done on an Eclipse based GSN editor. We report case studies on previous works about GSN and show the applicability of the design and implementation. This is a step toward developing an assurance case language.
