Architecture Level Qualitative Reasoning About Safety

Architects use a variety of techniques to evaluate designs for the desired levels of specific quality attributes. Reasoning frameworks are used to guide architecture definition by determining the extent to which a software architecture satisfies its quality requirements. There is much work on reasoning about quality attributes such as performance and modifiability but there has been little work on defining a reasoning framework for safety. We present a safety reasoning framework that is based on the observation that safety hazards lead to accidents when certain other quality requirements of the system are not satisfied. This naturally leads to the use of reasoning frameworks for these other attributes as a means to indirectly reason about safety. We present our technique for using standard safety engineering activities to provide the data needed for the safety reasoning framework. A riskbased qualitative reasoning technique is used to combine the results from the set of reasoning frameworks and make a judgment on satisfaction of safety requirements by the