86 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
Matching in the Pi-Calculus
We study whether, in the pi-calculus, the match prefix-a conditional operator
testing two names for (syntactic) equality-is expressible via the other
operators. Previously, Carbone and Maffeis proved that matching is not
expressible this way under rather strong requirements (preservation and
reflection of observables). Later on, Gorla developed a by now widely-tested
set of criteria for encodings that allows much more freedom (e.g. instead of
direct translations of observables it allows comparison of calculi with respect
to reachability of successful states). In this paper, we offer a considerably
stronger separation result on the non-expressibility of matching using only
Gorla's relaxed requirements.Comment: In Proceedings EXPRESS/SOS 2014, arXiv:1408.127
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
Matching in the Pi-Calculus (Technical Report)
We study whether, in the pi-calculus, the match prefix---a conditional
operator testing two names for (syntactic) equality---is expressible via the
other operators. Previously, Carbone and Maffeis proved that matching is not
expressible this way under rather strong requirements (preservation and
reflection of observables). Later on, Gorla developed a by now widely-tested
set of criteria for encodings that allows much more freedom (e.g. instead of
direct translations of observables it allows comparison of calculi with respect
to reachability of successful states). In this paper, we offer a considerably
stronger separation result on the non-expressibility of matching using only
Gorla's relaxed requirements.Comment: This report extends a paper in EXPRESS/SOS'14 and provides the
missing proof
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
Probabilistic Operational Correspondence
Encodings are the main way to compare process calculi. By applying quality criteria to encodings we analyse their quality and rule out trivial or meaningless encodings. Thereby, operational correspondence is one of the most common and most important quality criteria. It ensures that processes and their translations have the same abstract behaviour. We analyse probabilistic versions of operational correspondence to enable such a verification for probabilistic systems.
Concretely, we present three versions of probabilistic operational correspondence: weak, middle, and strong. We show the relevance of the weaker version using an encoding from a sublanguage of probabilistic CCS into the probabilistic ?-calculus. Moreover, we map this version of probabilistic operational correspondence onto a probabilistic behavioural relation that directly relates source and target terms. Then we can analyse the quality of the criterion by analysing the relation it induces between a source term and its translation. For the second version of probabilistic operational correspondence we proceed in the opposite direction. We start with a standard simulation relation for probabilistic systems and map it onto a probabilistic operational correspondence criterion
Musings on Encodings and Expressiveness
This paper proposes a definition of what it means for one system description
language to encode another one, thereby enabling an ordering of system
description languages with respect to expressive power. I compare the proposed
definition with other definitions of encoding and expressiveness found in the
literature, and illustrate it on a case study: comparing the expressive power
of CCS and CSP.Comment: In Proceedings EXPRESS/SOS 2012, arXiv:1208.244
On the relative expressiveness of higher-order session processes
By integrating constructs from the Ī»-calculus and the Ļ-calculus, in higher-order process calculi exchanged values may contain processes. This paper studies the relative expressiveness of HOĻ, the higher-order Ļ-calculus in which communications are governed by session types. Our main discovery is that HO, a subcalculus of HOĻ 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 HOĻ fully abstractly (upĀ to typed contextual equivalence) more precisely and efficiently than the first-order session Ļ-calculus (Ļ). Overall, under session types, HOĻ, HO, and Ļ are equally expressive; however, HOĻ and HO are more tightly related than HOĻ and Ļ
Priorities Without Priorities: Representing Preemption in Psi-Calculi
Psi-calculi is a parametric framework for extensions of the pi-calculus with
data terms and arbitrary logics. In this framework there is no direct way to
represent action priorities, where an action can execute only if all other
enabled actions have lower priority. We here demonstrate that the psi-calculi
parameters can be chosen such that the effect of action priorities can be
encoded.
To accomplish this we define an extension of psi-calculi with action
priorities, and show that for every calculus in the extended framework there is
a corresponding ordinary psi-calculus, without priorities, and a translation
between them that satisfies strong operational correspondence. This is a
significantly stronger result than for most encodings between process calculi
in the literature.
We also formally prove in Nominal Isabelle that the standard congruence and
structural laws about strong bisimulation hold in psi-calculi extended with
priorities.Comment: In Proceedings EXPRESS/SOS 2014, arXiv:1408.127
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