Systematic incremental validation of rule-based reactive systems

Validating the specification of a reactive system, such as a telephone switching system, traffic controller, or automated network service, is difficult, primarily because it is extremely hard even to state a complete and correct set of requirements, let alone to prove that a specification satisfies them. A previous paper, R.J. Hall(1993), described a new validation proof technique, sound scenario generalization, which computes and proves a general validation lemma from a specific requirement-scenario and a candidate specification. That paper left open how the user should employ the technique to systematically validate a complete system. This paper describes an approach, based on a novel knowledge structure called a library of generalized scenario fragments, that combines the advantages of traditional software testing and automated theorem proving of specifications, avoiding most of their shortcomings. I also describe preliminary experience with ISAT-VA, a prototype of such an assistant.<>