Reusing Requirements: The Need for Extended Variability Models

The paper describes a product-line-oriented approach to reusing requirements for systems with highly complex variability. Software product lines are a powerful means to manage comprehensively of all artifacts produced during system development for reuse. Hence, classical product line approaches provide mechanisms to handle requirements for reuse. But especially in the context of automotive systems, we face the challenge of creating reusable requirements specifications that each contain variability; reuse for requirements specifications of this kind means handling variability of variability models. This paper describes techniques for generating requirements specifications with variability from a so-called requirements library. The research results described originate from a process improvement initiative at DaimlerChrysler. The presented approaches are therefore pragmatic and aimed at current industrial practice but are formally based on a category-theoretical notation. Driven by practical issues, the paper comes up with extended means for variability modeling and a new notion of variability, broadening the scope of what can be managed by product lines.