Capturing requirements for legacy systems

We recommend both a top-down and bottom-up approach to requirements recovery. The position of this paper is that requirements must be recovered from sources other than code and substantiated against the recovered design. In this paper, we provide details on a case study in which we recovered requirements for the A-6E, a navy attack aircraft. We used Software Cost Reduction (SCR) tabular methods to capture "black box" requirements precisely, and developed analysis techniques to check decision table logic. The SCR tables are excellent for capturing both system and software requirements, and are a primary element of the new Software Productivity Consortium requirements method CoRE.