A Measures and Metrics Framework for Software Safety

A set of software-safety metrics is presented in this paper. The proposed metrics framework is intended to address software-safety risk assessment and can be used to evaluate the software-safety quality of a process. The framework attempts to assess safety risks from the beginning of the software development lifecycle and helps to implement efficient solutions. The complete framework is based on McCall's Factors, Criteria and Metrics approach and useful for assessing the degree of safety risk prevalence. The objective is to identify software elements that can lead to accidents if not properly addressed with the support of the safety engineering and software engineering disciplines. Various safety analysis methods including hazard analysis, standards, and guidelines are reviewed for their limitations and practical problems are considered. The framework considers measures that contribute to safety assessment through metrics in each of the Software Development Life Cycle phase. An experimental laboratory setup as 'Safety-Critical System' called Railroad Crossing Critical System (RCCS), which implements a safety-critical software, is used for demonstration and to validate the utility of the framework.