Refinement of decomposed models by interface instantiation

•A limited form of refinement called interface instantiation is proposed for the Event-B formalism.•Interface instantiation equips Event-B with a technique for shared-variable refinement.•Interface instantiation fits seamlessly with Event-B decomposition and refinement.•A worked out example is used to demonstrate this.•A correctness proof is provided.

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.