Rationale Software engineering aims to develop software by using approaches which en able large and complex program suites to be developed in a systematic way. However, it is well known that it is difficult to obtain the level of assurance of correctness required for safety critical software using old fashioned program ming techniques. The level of safety required becomes particularly high in software which is to function without a break for long periods of time, since the software cannot be restarted and errors can accumulate. Consequently programming for mission critical systems, for...