217 research outputs found
Axiomatizing Maximal Progress and Discrete Time
Milner's complete proof system for observational congruence is crucially
based on the possibility to equate divergent expressions to
non-divergent ones by means of the axiom .
In the presence of a notion of priority, where, e.g., actions of type
have a lower priority than silent actions, this axiom is no longer
sound. Such a form of priority is, however, common in timed process algebra,
where, due to the interpretation of as a time delay, it naturally
arises from the maximal progress assumption. We here present our solution,
based on introducing an auxiliary operator defining a "priority
scope", to the long time open problem of axiomatizing priority using standard
observational congruence: we provide a complete axiomatization for a basic
process algebra with priority and (unguarded) recursion. We also show that,
when the setting is extended by considering static operators of a discrete time
calculus, an axiomatization that is complete over (a characterization of)
finite-state terms can be developed by re-using techniques devised in the
context of a cooperation with Prof. Jos Baeten
Read Operators and their Expressiveness in Process Algebras
We study two different ways to enhance PAFAS, a process algebra for modelling
asynchronous timed concurrent systems, with non-blocking reading actions. We
first add reading in the form of a read-action prefix operator. This operator
is very flexible, but its somewhat complex semantics requires two types of
transition relations. We also present a read-set prefix operator with a simpler
semantics, but with syntactic restrictions. We discuss the expressiveness of
read prefixes; in particular, we compare them to read-arcs in Petri nets and
justify the simple semantics of the second variant by showing that its
processes can be translated into processes of the first with timed-bisimilar
behaviour. It is still an open problem whether the first algebra is more
expressive than the second; we give a number of laws that are interesting in
their own right, and can help to find a backward translation.Comment: In Proceedings EXPRESS 2011, arXiv:1108.407
Process algebra for performance evaluation
This paper surveys the theoretical developments in the field of stochastic process algebras, process algebras where action occurrences may be subject to a delay that is determined by a random variable. A huge class of resource-sharing systems – like large-scale computers, client–server architectures, networks – can accurately be described using such stochastic specification formalisms. The main emphasis of this paper is the treatment of operational semantics, notions of equivalence, and (sound and complete) axiomatisations of these equivalences for different types of Markovian process algebras, where delays are governed by exponential distributions. Starting from a simple actionless algebra for describing time-homogeneous continuous-time Markov chains, we consider the integration of actions and random delays both as a single entity (like in known Markovian process algebras like TIPP, PEPA and EMPA) and as separate entities (like in the timed process algebras timed CSP and TCCS). In total we consider four related calculi and investigate their relationship to existing Markovian process algebras. We also briefly indicate how one can profit from the separation of time and actions when incorporating more general, non-Markovian distributions
Extensions of Standard Weak Bisimulation Machinery: Finite-state General Processes, Refinable Actions, Maximal-progress and Time
AbstractWe present our work on extending the standard machinery for weak bisimulation to deal with: finite-state processes of calculi with a full signature, including static operators like parallel; semantic action refinement and ST bisimulation; maximal-progress, i.e. priority of standard actions over unprioritized actions; representation of time: discrete real-time and Markovian stochastic time. For every such topic we show that it is possible to resort simply to weak bisimulation and that we can exploit this to obtain, via modifications to the standard machinery: finite-stateness of semantic models when static operators are not replicable by recursion, as for CCS with the standard semantics, thus yielding decidability of equivalence; structural operational semantics for terms; a complete axiomatization for finite-state processes via a modification of the standard theory of standard equation sets and of the normal-form derivation procedure
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