Hoare-Style Verification of Graph Programs

GP (for Graph Programs) is an experimental nondeterministic programming language for solving problems on graphs and graph-like structures. The language is based on graph transformation rules, allowing visual programming at a high level of abstraction. In particular, GP frees programmers from dealing with low-level data structures. In this paper, we present a Hoare-style proof system for verifying the partial correctness of (a subset of) graph programs. The preand postconditions of the calculus are nested graph conditions with expressions, a formalism for specifying both structural graph properties and properties of labels. We show that our proof system is sound with respect to GP’s operational semantics and give examples of its use.