High assurance engineering: the good, the bad, and the ugly

Over the past two decades, substantial research efforts have been devoted to the design and development of high assurance systems, including general approaches and specific systems. Researchers in fault tolerant systems have developed effective approaches to handle hardware and software failures and provide high system reliability and availability. Techniques for developing high assurance systems span a wide spectrum, ranging from informal to formal methods, from cost-effective to highly expensive approaches, and from ad-hoc to theoretically sound mechanisms. As an informal classification, the paper categorizes these techniques into the good, the bad, and the ugly.