Recent efforts in the automotive domain to initiate a para- digm-shift from a traditional hardware-driven to a function-driven development process create new challenges to tackle. A hardware-driven variant handling mechanism will get more and more inappropriate. Instead, new concepts and methods are necessary to model and configure concrete systems. A software document which is used in the early phase of development is the so called function net model. Variability in function nets is captured implicitly and is strongly dependent on the hardware infrastructure, constraints are collected with informal annotations, and variants are generated manually. This results in a situation where function nets get too complex, time consuming and unsuitable for future standards. In this paper, we will present a model-driven approach for function nets to capture variability explicitly, to express formal constraints, and to generate concrete variants with the support of an automated configuration process. By this, it is possible to use the generated variants as skeletons for virtual prototyping, so that requirement specifications can be verified efficiently.