Pp. 243-251 in Reliable Software, vol. 2. Maidenhead, England: Infotech State of the Art Report, 1977.


In an attempt to clarify the concept of software reliability, several concrete situations related to it are first discussed. Reliability is subsequently viewed as a relation between software system behaviour and human expectations. From a discussion of software correctness it is concluded that software reliability must refer to systems that include stochastic elements. In software systems such elements are associated with the hardware and the people who are part of the system. Reliability in the presence of stochastic elements requires stability. This may be achieved through special protection of sensitive system parts. Design for reliability may follow several policies: reduction of expectations; checking and quick recovery; careful and correct design.