Product-line Requirements Specification (PRS): an approach and case study

Software product-line engineering can provide significant gains in quality and productivity, through systematic reuse of software's conceptual structures. For embedded safety- or mission-critical systems, much of the development effort goes into understanding, specifying, and validating the requirements. If developers can re-use rather than re-do requirements for families of similar systems, we can improve productivity while significantly reducing the opportunity for requirements errors. This paper describes a systematic approach to developing a Product-line Requirements Specification (PRS) for such systems. The PRS explicitly represents the family's common requirements as well as the allowed variations that distinguish family members. When completed, the PRS definition also supports generation of well-formed Software Requirements Specifications (SRS) for members of the product line. We describe a process for developing a PRS starting from an analysis of a program family's commonalities and variabilities. The approach is illustrated with examples from a case study of a real family of systems, the Rockwell Collins Commercial Flight Control System product-line.