Management of change in structured verification

The use of formal methods in large complex applications implies the need for an evolutionary formal program development in which specification and verification phases are interleaved. Any change of a specification either by adding new parts or by changing erroneous parts affects existing verification work in a subtle way. We present a truth maintenance system for structured specification and verification. It is based on the simple but powerful notion of a development graph as an underlying data structure to represent an actual consistent state of a formal development. Based on this notion we try to minimize the consequences of changes of existing verification work.