2,723 research outputs found
Expressiveness of Process Algebras
AbstractWe examine ways to measure expressiveness of process algebras, and recapitulate and compare some related results from the literature
Expressiveness modulo Bisimilarity of Regular Expressions with Parallel Composition (Extended Abstract)
The languages accepted by finite automata are precisely the languages denoted
by regular expressions. In contrast, finite automata may exhibit behaviours
that cannot be described by regular expressions up to bisimilarity. In this
paper, we consider extensions of the theory of regular expressions with various
forms of parallel composition and study the effect on expressiveness. First we
prove that adding pure interleaving to the theory of regular expressions
strictly increases its expressiveness up to bisimilarity. Then, we prove that
replacing the operation for pure interleaving by ACP-style parallel composition
gives a further increase in expressiveness. Finally, we prove that the theory
of regular expressions with ACP-style parallel composition and encapsulation is
expressive enough to express all finite automata up to bisimilarity. Our
results extend the expressiveness results obtained by Bergstra, Bethke and
Ponse for process algebras with (the binary variant of) Kleene's star
operation.Comment: In Proceedings EXPRESS'10, arXiv:1011.601
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
On Modelling and Analysis of Dynamic Reconfiguration of Dependable Real-Time Systems
This paper motivates the need for a formalism for the modelling and analysis
of dynamic reconfiguration of dependable real-time systems. We present
requirements that the formalism must meet, and use these to evaluate well
established formalisms and two process algebras that we have been developing,
namely, Webpi and CCSdp. A simple case study is developed to illustrate the
modelling power of these two formalisms. The paper shows how Webpi and CCSdp
represent a significant step forward in modelling adaptive and dependable
real-time systems.Comment: Presented and published at DEPEND 201
A modular approach to defining and characterising notions of simulation
We propose a modular approach to defining notions of simulation, and modal logics which characterise them. We use coalgebras to model state-based systems, relators to define notions of simulation for such systems, and inductive techniques to define the syntax and semantics of modal logics for coalgebras. We show that the expressiveness of an inductively defined logic for coalgebras w.r.t. a notion of simulation follows from an expressivity condition involving one step in the definition of the logic, and the relator inducing that notion of simulation. Moreover, we show that notions of simulation and associated characterising logics for increasingly complex system types can be derived by lifting the operations used to combine system types, to a relational level as well as to a logical level. We use these results to obtain Baltagās logic for coalgebraic simulation, as well as notions of simulation and associated logics for a large class of non-deterministic and probabilistic systems
On the Expressiveness of Markovian Process Calculi with Durational and Durationless Actions
Several Markovian process calculi have been proposed in the literature, which
differ from each other for various aspects. With regard to the action
representation, we distinguish between integrated-time Markovian process
calculi, in which every action has an exponentially distributed duration
associated with it, and orthogonal-time Markovian process calculi, in which
action execution is separated from time passing. Similar to deterministically
timed process calculi, we show that these two options are not irreconcilable by
exhibiting three mappings from an integrated-time Markovian process calculus to
an orthogonal-time Markovian process calculus that preserve the behavioral
equivalence of process terms under different interpretations of action
execution: eagerness, laziness, and maximal progress. The mappings are limited
to classes of process terms of the integrated-time Markovian process calculus
with restrictions on parallel composition and do not involve the full
capability of the orthogonal-time Markovian process calculus of expressing
nondeterministic choices, thus elucidating the only two important differences
between the two calculi: their synchronization disciplines and their ways of
solving choices
Web Services: A Process Algebra Approach
It is now well-admitted that formal methods are helpful for many issues
raised in the Web service area. In this paper we present a framework for the
design and verification of WSs using process algebras and their tools. We
define a two-way mapping between abstract specifications written using these
calculi and executable Web services written in BPEL4WS. Several choices are
available: design and correct errors in BPEL4WS, using process algebra
verification tools, or design and correct in process algebra and automatically
obtaining the corresponding BPEL4WS code. The approaches can be combined.
Process algebra are not useful only for temporal logic verification: we remark
the use of simulation/bisimulation both for verification and for the
hierarchical refinement design method. It is worth noting that our approach
allows the use of any process algebra depending on the needs of the user at
different levels (expressiveness, existence of reasoning tools, user
expertise)
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
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