Consistency is a major issue that must be properly addressed when considering multiple view architectures. In this paper, we provide a formal definition of views expressed graphically using diagrams with multiplicities and propose a simple algorithm to check the consistency of diagrams. We also put forward a simple language of constraints to express more precise (intra-view and inter-view) consistency requirements. We sketch a complete decision procedure to decide whether diagrams satisfy a given constraint expressed in this language. Our framework is illustrated with excerpts of a case study: the specification of the architecture of a train control system.