Reverse engineering is reverse forward engineering

Reverse engineering is focused on the challenging task of understanding legacy program code without having suitable documentation. Using a transformational forward engineering perspective, we gain the insight that much of this difficulty is caused by design decisions made during system development. Such decisions "hide" the program functionality and performance requirements in the final system by applying repeated refinements through layers of abstraction and information-spreading optimizations, both of which change representations and force single program entities to serve multiple purposes. To be able to reverse engineer, we essentially have to reverse these design decisions. Following the transformational approach, we can use the transformations of a forward engineering methodology and apply them "backwards" to reverse engineer code to a more abstract specification. Since most existing code was not generated by transformational synthesis, this produces a plausible formal transformational design rather than the original authors' actual design. A by-product of the transformational reverse engineering process is a design database for the program that then can be maintained to minimize the need for further reverse engineering during the remaining lifetime of the system. A consequence of this perspective is the belief that plan recognition methods are not sufficient for reverse engineering. As an example, a small fragment of a real-time operating system is reverse-engineered using this approach.