On the Nature and Content of Safety Contracts

Component-based software engineering researchers have explored component reuse, typically at the source-code level. Contracts explicitly describe component behaviour, reducing development risk by exposing potential incompatibilities early. But to benefit fully from reuse, developers of safety-critical systems must also reuse safety evidence. Full reuse would require both extending the existing notion of component contracts to cover safety properties and using these contracts in both component selection and system certification. In this paper, we explore some of the ways in which this is not as simple as it first appears.