Supporting the use of COTS in safety critical applications

With the growing complexity and costs involved with the development of safety-critical applications, the possibility of building systems using pre-existing commercial off-the-shelf (COTS) components becomes increasingly attractive. However, a number of problems are posed by attempting to integrate COTS components, as they exist at the moment, into larger system developments, including: (a) the potential for introducing systematic errors through component mismatch, and (b) meeting the obligations of the system safety case. In this paper, we briefly describe these two problems and argue how they can both be alleviated by appropriate and sufficient component documentation. In an ideal world, additional component information that documents all the critical design features of the component and required safety evidence would be provided by the COTS component suppliers. However, in the absence of this happening, it is important for developers using COTS components to record their own thinking regarding a component (e.g. assumptions), so that, at the very least, this information can be peer-reviewed and used consistently throughout a development. Through documenting COTS components using a sufficiently clear and expressive notation, we would expect to alleviate, at least to some extent, the problems of applying COTS in safety-critical applications.