Extending Symmetry Reduction by Exploiting System Architecture

Symmetry reduction is a technique to alleviate state explosion in model checking by replacing a model of replicated processes with a bisimilar quotient model. The size of the quotient depends strongly on the set of applicable symmetries, which in many practical cases allows only polynomial reduction. We introduce architectural symmetry, a concept that exploits architectural system features to compensate for a lack of symmetry in the system model. We show that the standard symmetry quotient of an architecturally symmetric and well-architected model preserves arbitrary Boolean combinations and nestings of reachability properties. This quotient can be exponentially smaller than the model, even in cases where traditional symmetry reduction is nearly ineffective. Our technique thus extends the benefits of symmetry reduction to systems that are in fact not symmetric. Finally, we generalize our results to all architecturally symmetric models, including those that are not well-architected. We illustrate our method through examples and experimental data.