Software safety assurance - what is sufficient?

It is possible to construct a safety argument for the software aspects of a system in order to demonstrate that the software is acceptably safe to operate. In order to be compelling, it is necessary to justify that the arguments and evidence presented for the software provide sufficient safety assurance. In this paper we consider how assurance may be explicitly considered when developing a software safety argument. We propose a framework for making and justifying decisions about the arguments and evidence required to assure the safety of the software.