Abstract. Decomposition is a technique to separate the design of a complex system into smaller sub-models, which improves scalability and team development. In the shared-variable decomposition approach for Event-B sub-models share external variables and communicate through external events which cannot be easily refined.
Our first contribution hence is a proposal for a new construct called interface that encapsulates the external variables, along with a mechanism for interface instantiation. Using the new construct and mechanism, external variables can be refined consistently. Our second contribution is an approach for verifying the correctness of Event-B extensions using the supporting Rodin tool. We illustrate our approach by proving the correctness of interface instantiation.
Keywords: Event-B, Decomposition, Refinement, External variables.