A criterion for separating process calculi

We introduce a new criterion, replacement freeness, to discern the relative expressiveness of process calculi. Intuitively, a calculus is strongly replacement free if replacing, within an enclosing context, a process that cannot perform any visible action by an arbitrary process never inhibits the capability of the resulting process to perform a visible action. We prove that there exists no compositional and interaction sensitive encoding of a not strongly replacement free calculus into any strongly replacement free one. We then define a weaker version of replacement freeness, by only considering replacement of closed processes, and prove that, if we additionally require the encoding to preserve name independence, it is not even possible to encode a non replacement free calculus into a weakly replacement free one. As a consequence of our encodability results, we get that many calculi equipped with priority are not replacement free and hence are not encodable into mainstream calculi like CCS and pi-calculus, that instead are strongly replacement free. We also prove that variants of pi-calculus with match among names, pattern matching or polyadic synchronization are only weakly replacement free, hence they are separated both from process calculi with priority and from mainstream calculi.Comment: In Proceedings EXPRESS'10, arXiv:1011.601

On the Expressiveness of Intensional Communication

The expressiveness of communication primitives has been explored in a common framework based on the pi-calculus by considering four features: synchronism (asynchronous vs synchronous), arity (monadic vs polyadic data), communication medium (shared dataspaces vs channel-based), and pattern-matching (binding to a name vs testing name equality). Here pattern-matching is generalised to account for terms with internal structure such as in recent calculi like Spi calculi, Concurrent Pattern Calculus and Psi calculi. This paper explores intensionality upon terms, in particular communication primitives that can match upon both names and structures. By means of possibility/impossibility of encodings, this paper shows that intensionality alone can encode synchronism, arity, communication-medium, and pattern-matching, yet no combination of these without intensionality can encode any intensional language.Comment: In Proceedings EXPRESS/SOS 2014, arXiv:1408.127

On the Expressiveness of Joining

The expressiveness of communication primitives has been explored in a common framework based on the pi-calculus by considering four features: synchronism (asynchronous vs synchronous), arity (monadic vs polyadic data), communication medium (shared dataspaces vs channel-based), and pattern-matching (binding to a name vs testing name equality vs intensionality). Here another dimension coordination is considered that accounts for the number of processes required for an interaction to occur. Coordination generalises binary languages such as pi-calculus to joining languages that combine inputs such as the Join Calculus and general rendezvous calculus. By means of possibility/impossibility of encodings, this paper shows coordination is unrelated to the other features. That is, joining languages are more expressive than binary languages, and no combination of the other features can encode a joining language into a binary language. Further, joining is not able to encode any of the other features unless they could be encoded otherwise.Comment: In Proceedings ICE 2015, arXiv:1508.04595. arXiv admin note: substantial text overlap with arXiv:1408.145

On the relative expressiveness of higher-order session processes

By integrating constructs from the λ-calculus and the π-calculus, in higher-order process calculi exchanged values may contain processes. This paper studies the relative expressiveness of HOπ, the higher-order π-calculus in which communications are governed by session types. Our main discovery is that HO, a subcalculus of HOπ which lacks name-passing and recursion, can serve as a new core calculus for session-typed higher-order concurrency. By exploring a new bisimulation for HO, we show that HO can encode HOπ fully abstractly (up to typed contextual equivalence) more precisely and efficiently than the first-order session π-calculus (π). Overall, under session types, HOπ, HO, and π are equally expressive; however, HOπ and HO are more tightly related than HOπ and π

Full abstraction for expressiveness: history, myths and facts

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.What does it mean that an encoding is fully abstract? What does it not mean? In this position paper, we want to help the reader to evaluate the real benefits of using such a notion when studying the expressiveness of programming languages. Several examples and counterexamples are given. In some cases, we work at a very abstract level; in other cases, we give concrete samples taken from the field of process calculi, where the theory of expressiveness has been mostly developed in the last years

Recursion vs Replication in Process Calculi: Expressiveness

International audienceIn this paper we shall survey and discuss in detail the work on the relative expressiveness of recursion and replication in various process calculi. Namely, CCS, the pi-calculus, and the Ambient calculus. We shall give evidence that the ability of expressing recursive behaviour via replication often depends on the scoping mechanisms of the given calculus which compensate for the restriction of replication

Expressiveness of Recursion, Replication and Scope Mechanisms in Process Calculi

International audienceIn this paper we shall survey and discuss in detail the work on the relative expressiveness of recursion and replication in various process calculi. Namely, CCS, the pi-calculus, the Ambient calculus, Concurrent Constraint Programming and calculi for Cryptographic Protocols. We shall give evidence that the ability of expressing recursive behaviour via replication often depends on the scoping mechanisms of the given calculus which compensate for the restriction of replication