19 research outputs found
Analysing and Comparing Encodability Criteria
Encodings or the proof of their absence are the main way to compare process
calculi. To analyse the quality of encodings and to rule out trivial or
meaningless encodings, they are augmented with quality criteria. There exists a
bunch of different criteria and different variants of criteria in order to
reason in different settings. This leads to incomparable results. Moreover it
is not always clear whether the criteria used to obtain a result in a
particular setting do indeed fit to this setting. We show how to formally
reason about and compare encodability criteria by mapping them on requirements
on a relation between source and target terms that is induced by the encoding
function. In particular we analyse the common criteria full abstraction,
operational correspondence, divergence reflection, success sensitiveness, and
respect of barbs; e.g. we analyse the exact nature of the simulation relation
(coupled simulation versus bisimulation) that is induced by different variants
of operational correspondence. This way we reduce the problem of analysing or
comparing encodability criteria to the better understood problem of comparing
relations on processes.Comment: In Proceedings EXPRESS/SOS 2015, arXiv:1508.06347. The Isabelle/HOL
source files, and a full proof document, are available in the Archive of
Formal Proofs, at
http://afp.sourceforge.net/entries/Encodability_Process_Calculi.shtm
On the expressiveness of forwarding in higher-order communication
Abstract. In higher-order process calculi the values exchanged in communications may contain processes. There are only two capabilities for received processes: execution and forwarding. Here we propose a limited form of forwarding: output actions can only communicate the parallel composition of statically known closed processes and processes received through previously executed input actions. We study the expressiveness of a higher-order process calculus featuring this style of communication. Our main result shows that in this calculus termination is decidable while convergence is undecidable.
When to Move to Transfer Nets On the limits of Petri nets as models for process calculi
International audiencePierpaolo Degano has been an influential pioneer in the investigation of Petri nets as models for concurrent process calculi (see e.g. the well-known seminal work by Degano–De Nicola–Montanari also known as DDM88). In this paper, we address the limits of classical Petri nets by discussing when it is necessary to move to the so-called Transfer nets, in which transitions can also move to a target place all the tokens currently present in a source place. More precisely, we consider a simple calculus of processes that interact by generating/consuming messages into/from a shared repository. For this calculus classical Petri nets can faithfully model the process behavior. Then we present a simple extension with a primitive allowing processes to atomically rename all the data of a given kind. We show that with the addition of such primitive it is necessary to move to Transfer nets to obtain a faithful modeling
On Bisimilarity and Substitution in Presence of Replication
International audienceWe prove a new congruence result for the pi-calculus: bisimilarity is a congruence in the sub-calculus that does not include restriction nor sum, and features top-level replications. Our proof relies on algebraic properties of replication, and on a new syntactic characterisation of bisimilarity. We obtain this characterisation using a rewriting system rather than a purely equational axiomatisation. We then deduce substitution closure, and hence, congruence. Whether bisimilarity is a congruence when replications are unrestricted remains open
Inseguendo fagiani selvatici: Partial order reduction for guarded command languages
This paper presents a method for testing whether objects in actor languages and active object languages exhibit locally deterministic behavior. We investigate such a method for a class of guarded command programs, abstracting from object-oriented features like method calls but focusing on cooperative scheduling of dynamically spawned processes executing in parallel. The proposed method can answer questions such as whether all permutations of an execution trace are equivalent, by generating candidate traces for testing which may lead to different final states. To prune the set of candidate traces, we employ partial order reduction. To further reduce the set, we introduce an analysis technique to decide whether a generated trace is schedulable. Schedulability cannot be decided for guarded commands using standard dependence and interference relations because guard enabledness is non-monotonic. To solve this problem, we use concolic execution to produce linearized symbolic traces of the executed program, which allows a weakest precondition computation to decide on the satisfiability of guards
Comparing Process Calculi Using Encodings
Encodings or the proof of their absence are the main way to compare process
calculi. To analyse the quality of encodings and to rule out trivial or
meaningless encodings, they are augmented with encodability criteria. There
exists a bunch of different criteria and different variants of criteria in
order to reason in different settings. This leads to incomparable results.
Moreover, it is not always clear whether the criteria used to obtain a result
in a particular setting do indeed fit to this setting. This paper provides a
short survey on often used encodability criteria, general frameworks that try
to provide a unified notion of the quality of an encoding, and methods to
analyse and compare encodability criteria.Comment: In Proceedings EXPRESS/SOS 2019, arXiv:1908.0821
Reactive Turing machines
We propose reactive Turing machines (RTMs), extending classical Turing machines with
a process-theoretical notion of interaction, and use it to define a notion of executable
transition system. We show that every computable transition system with a bounded
branching degree is simulated modulo divergence-preserving branching bisimilarity by
an RTM, and that every effective transition system is simulated modulo the variant of
branching bisimilarity that does not require divergence preservation. We conclude from
these results that the parallel composition of (communicating) RTMs can be simulated by
a single RTM. We prove that there exist universal RTMs modulo branching bisimilarity, but
these essentially employ divergence to be able to simulate an RTM of arbitrary branching
degree. We also prove that modulo divergence-preserving branching bisimilarity there are
RTMs that are universal up to their own branching degree. We establish a correspondence
between executability and finite definability in a simple process calculus. Finally, we
establish that RTMs are at least as expressive as persistent Turing machines