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Sensoria Bibliography Site On the Expressive Power of Global and Local Priority in Process Calculi
Cristian Versari, Nadia Busi, Roberto Gorrieri
abstract:
Priority is a frequently used feature of many computational systems. In this paper we study the expressiveness of two process algebras enriched with different priority mechanisms. In particular, we consider a finite (i.e. recursion-free) fragment of asynchronous CCS with global priority (FAP, for short) and Phillipsâ CPG (CCS with local priority), and we contrast their expressive power with that of two non-prioritised calculi, namely the pi-calculus and its broadcast-based version, called bpi. We prove, by means of leader-election-based separation results, that there exists no encoding of FAP into pi-Calculus or CPG, under certain conditions. Moreover, we single out another problem in distributed computing, we call the last man standing problem (LMS for short), that better reveals the gap between the two prioritised calculi above and the two non prioritised ones, by proving that there exists no parallel-preserving encoding of the prioritised calculi into the non-prioritised calculi retaining any sincere (complete but partially correct, i.e., admitting divergence or premature termination) semantics.