Dependability Cases

Many large software systems display fragility or a lack of dependability caused by inattention to details at various stages of development (e.g., missing data, undocumented assumptions, lack of testing), resulting in a failure to catch errors. This technical note explains how to create a dependability case for a system that helps identify and keep track of such details. A dependability case is defined here as a structured argument providing evidence that a system meets its specified dependability requirements. The technical note describes how to structure the argument and present evidence to support it. A sample problem is presented, as well as issues raised by that problem and future goals.