When developing a Service-Oriented Architecture(SOA), analyzing the business process is even more important than in normal software projects. Nevertheless, most of the requirements artifacts used in normal software projects apply to SOA-projects, too. This results in competing requirement models (like use cases and business processes) that duplicate information in parts. Even worse, these models are often contradictory, belong to different types of stakeholders, and need much effort to be synchronized. However, these inconsistencies are an important source for requirements. We propose to deliberately switch between different perspectives onto the requirements to clarify them as soon as possible. In this way we a) enrich feedback and b) improve existing models as a by-product by confronting stakeholders with new perspectives. User interface mockups, data models, and business processes complement, enrich, and facilitate a pure use case perspective. We present a set of computer-supported techniques that leverage this friction between models and share our experiences in applying them.