Congruent Weak Conformance, a Partial Order among Processes

This paper presents a new property between processes arising from a set of relations called weak conformations. The largest, called weak conformance, is analogous to Milner’s observational equivalence. Unlike observational equivalence, however, weak conformance is not an equivalence but rather a preorder between processes. Like the previous property of logic conformance, weak conformance allows behaviors in the implementation that are unreachable in the specification. Unlike logic conformance, however, weak conformance exploits output concurrencies and allows interleaving of extraneous output actions in the implementation. Finally, reasonable restrictions in CCS syntax strengthen weak conformance to a precongruence. The resulting property, congruent weak conformance, forms a partial ordering among processes. As a precongruence, it models safe substitution of hardware.