Variability is a central concept in software product-line engineering. Feature Models are a well accepted technique to model variants and invariants within the automotive industry. Feature models are able to express variability through mandatory, optional, and alternative features of a product. Unfortunately the variability information is localised in the feature models and difficult to transfer to other requirements artefacts (e.g. use cases) to express dependencies between different requirements artefacts of a variant. This paper presents a self-contained model to explicitly represent the product-line variability in one central model, and further enables the definition of variability in different requirements models.