Petri Games: Synthesis of Distributed Systems with Causal Memory

We present a new multiplayer game model for the interaction and the flow of information in a distributed system. The players are tokens on a Petri net. As long as the players move in independent parts of the net, they do not know of each other; when they synchronize at a joint transition, each player gets informed of the causal history of the other player. We show that for Petri games with a single environment player and an arbitrary bounded number of system players, deciding the existence of a safety strategy for the system players is EXPTIME-complete.Comment: In Proceedings GandALF 2014, arXiv:1408.556

Correctness of concurrent processes

A new notion of correctness for concurrent processes is introduced and investigated. It is a relationship P sat S between process terms P built up from operators of CCS [Mi 80], CSP [Ho 85] and COSY [LTS 79] and logical formulas S specifying sets of finite communication sequences as in [Zw 89]. The definition of P sat S is based on a Petri net semantics for process terms [Ol 89]. The main point is that P sat S requires a simple liveness property of the net denoted by P. This implies that P is divergence free and externally deterministic. Process correctness P sat S determines a new semantic model for process terms and logical formulas. It is a modification ℜ* of the readiness semantics [OH 86] which is fully abstract with respect to the relation P sat S. The model ℜ* abstracts from the concurrent behaviour of process terms and certain aspects of their internal activity. In ℜ* process correctness P sat S boils down to semantic equality: ℜ*[P]=ℜ*[S]. The modified readiness equivalence is closely related to failure equivalence [BHR 84] and strong testing equivalence [DH 84]

Nondeterminism and Guarded Commands

The purpose of this paper is to discuss the relevance of nondeterminism in computer science, with a special emphasis on Dijkstra's guarded commands language.Comment: 34 pages. This is authors' version of Chapter 8 of the book K.R. Apt and C.A.R. Hoare (editors), Edsger Wybe Dijkstra: His Life, Work, and Legacy, volume 45 of ACM Books. ACM/Morgan & Claypool, 202

Proof rules and transformations dealing with fairness

AbstractWe provide proof rules enabling the treatment of two fairness assumptions in the context of Dijkstra's do-od-programs. These proof rules are derived by considering a transformed version of the original program which uses random assignments z≔? and admits only fair computations. Various, increasingly complicated, examples are discussed. In all cases reasonably simple proofs can be given. The proof rules use well-founded structures corresponding to infinite ordinals and deal with the original programs and not their translated versions