Developing high assurance avionics systems with the SCR requirements method

The SCR (Software Cost Reduction) requirements method is a formal method based on tables for the specification and analysis of the required behavior of safety-critical software systems. Originally developed in 1978 by NRL (Naval Research Laboratory) to document the flight program requirements of the Navy's A-7 aircraft, SCR has also been applied by a number of organizations in industry to a wide range of practical systems, including avionics and space systems. For example, in 1994, in the largest application of SCR to date, Lockheed used SCR to specify the requirements of the C-130J flight control software, which contains more than 250,000 lines of Ada code. To provide tool support for the SCR method, our group at NRL has developed an integrated suite of tools called the SCR toolset. The toolset includes a consistency checker for checking the specification for type errors and missing cases.