HYASM: A Tool to Verify Hierarchical Systems

Hierarchical state machines represent a natural and useful framework to model and reason about modern systems. These machines encompass the ability to model hierarchical systems where some of the components can be reused in different contexts, e.g., by hierarchically calling subsystems. However, classical model checkers lack support to properly deal with hierarchical systems. Mostly, they treat the hierarchical calls as generic, possibly recursive, procedure calls. In this paper, we present HYASM a model checker for hierarchical systems as an extension of the tool YASM, a symbolic model-checker based on the CEGAR paradigm. Our tool uses a suitable flattening approach over hierarchical state machines, and experimental results show that our approach works very well in practice.