A Graded Approach to Requirement Satisfaction for Evolving Systems

There has been a strong trend towards autonomous and semi-autonomous systems in recent years. Evolving and adaptive systems embody the notion of autonomy, by changing their behavior (and possibly their structure) in response to changes in their environment. A consequence is that a designer may not be able to fully define the functional behavior of a system. Hence, formal verification and testing may not be possible. As a result, the self-adapting aspect of an evolving system is often implemented in an informal, ad hoc, manner and there is potential for causing significant harm if a system malfunctions in some way. A safety case requires more than an assertion that a system will work because it has not failed in testing. A more rigorous approach is essential, in which we can formally show that an evolving system meets its requirements and specifications. This paper outlines initial work in combining the X-mu approach (to model fuzzy uncertainty) with flexible requirements for an evolving system specified in RELAX, a formal framework to capture the uncertainty in evolving system requirements. A simple case study is used to illustrate some of the principles.