Extending ERS for Modelling Dynamic Workflows in Event-B

Event-B is a state-based formal method for modelling and verifying the consistency of discrete systems. Event refinement structures (ERS) augment Event-B with hierarchical diagrams, providing explicit support for workflows and refinement relationships. Despite the variety of ERS combinators, ERS still lacks the flexibility to model dynamic workflows that support dynamic changes in the degree of concurrency. Specifically in the cases where the degree of parallelism is data dependent and data values can change during execution. In this paper, we propose two types of extensions in ERS to support dynamic modelling using Event-B. The first extension is supporting data-dependent workflows where data changes are possible. The second extension improves ERS by providing exception handling support. Semantics are given to an ERS diagram by generating an Event-B model from it. We demonstrate the Event-B encodings of the proposed ERS extensions by modelling a concurrent emergency dispatch case study.