1,540 research outputs found
Talking quiescence: a rigorous theory that supports parallel composition, action hiding and determinisation
The notion of quiescence - the absence of outputs - is vital in both
behavioural modelling and testing theory. Although the need for quiescence was
already recognised in the 90s, it has only been treated as a second-class
citizen thus far. This paper moves quiescence into the foreground and
introduces the notion of quiescent transition systems (QTSs): an extension of
regular input-output transition systems (IOTSs) in which quiescence is
represented explicitly, via quiescent transitions. Four carefully crafted rules
on the use of quiescent transitions ensure that our QTSs naturally capture
quiescent behaviour.
We present the building blocks for a comprehensive theory on QTSs supporting
parallel composition, action hiding and determinisation. In particular, we
prove that these operations preserve all the aforementioned rules.
Additionally, we provide a way to transform existing IOTSs into QTSs, allowing
even IOTSs as input that already contain some quiescent transitions. As an
important application, we show how our QTS framework simplifies the fundamental
model-based testing theory formalised around ioco.Comment: In Proceedings MBT 2012, arXiv:1202.582
Using schedulers to test probabilistic distributed systems
This is the author's accepted manuscript. The final publication is available at Springer via http://dx.doi.org/10.1007/s00165-012-0244-5. Copyright Ā© 2012, British Computer Society.Formal methods are one of the most important approaches to increasing the confidence in the correctness of software systems. A formal specification can be used as an oracle in testing since one can determine whether an observed behaviour is allowed by the specification. This is an important feature of formal testing: behaviours of the system observed in testing are compared with the specification and ideally this comparison is automated. In this paper we study a formal testing framework to deal with systems that interact with their environment at physically distributed interfaces, called ports, and where choices between different possibilities are probabilistically quantified. Building on previous work, we introduce two families of schedulers to resolve nondeterministic choices among different actions of the system. The first type of schedulers, which we call global schedulers, resolves nondeterministic choices by representing the environment as a single global scheduler. The second type, which we call localised schedulers, models the environment as a set of schedulers with there being one scheduler for each port. We formally define the application of schedulers to systems and provide and study different implementation relations in this setting
Modeling and Analysis of Power-Aware Systems
The paper describes a formal approach for designing and reasoning about power-constrained, timed systems. The framework is based on process algebra, a formalism that has been developed to describe and analyze communicating concurrent systems. The proposed extension allows the modeling of probabilistic resource failures, priorities of resource usages, and power consumption by resources within the same formalism. Thus, it is possible to model alternative power-consumption behaviors and analyze tradeoffs in their timing and other characteristics. This paper describes the modeling and analysis techniques, and illustrates them with examples, including a dynamic voltage-scaling algorithm
Timed Parity Games: Complexity and Robustness
We consider two-player games played in real time on game structures with
clocks where the objectives of players are described using parity conditions.
The games are \emph{concurrent} in that at each turn, both players
independently propose a time delay and an action, and the action with the
shorter delay is chosen. To prevent a player from winning by blocking time, we
restrict each player to play strategies that ensure that the player cannot be
responsible for causing a zeno run. First, we present an efficient reduction of
these games to \emph{turn-based} (i.e., not concurrent) \emph{finite-state}
(i.e., untimed) parity games. Our reduction improves the best known complexity
for solving timed parity games. Moreover, the rich class of algorithms for
classical parity games can now be applied to timed parity games. The states of
the resulting game are based on clock regions of the original game, and the
state space of the finite game is linear in the size of the region graph.
Second, we consider two restricted classes of strategies for the player that
represents the controller in a real-time synthesis problem, namely,
\emph{limit-robust} and \emph{bounded-robust} winning strategies. Using a
limit-robust winning strategy, the controller cannot choose an exact
real-valued time delay but must allow for some nonzero jitter in each of its
actions. If there is a given lower bound on the jitter, then the strategy is
bounded-robust winning. We show that exact strategies are more powerful than
limit-robust strategies, which are more powerful than bounded-robust winning
strategies for any bound. For both kinds of robust strategies, we present
efficient reductions to standard timed automaton games. These reductions
provide algorithms for the synthesis of robust real-time controllers
Testing Reactive Probabilistic Processes
We define a testing equivalence in the spirit of De Nicola and Hennessy for
reactive probabilistic processes, i.e. for processes where the internal
nondeterminism is due to random behaviour. We characterize the testing
equivalence in terms of ready-traces. From the characterization it follows that
the equivalence is insensitive to the exact moment in time in which an internal
probabilistic choice occurs, which is inherent from the original testing
equivalence of De Nicola and Hennessy. We also show decidability of the testing
equivalence for finite systems for which the complete model may not be known
Probabilistic Mobility Models for Mobile and Wireless Networks
International audienceIn this paper we present a probabilistic broadcast calculus for mobile and wireless networks whose connections are unreliable. In our calculus, broadcasted messages can be lost with a certain probability, and due to mobility the connection probabilities may change. If a network broadcasts a message from a location, it will evolve to a network distribution depending on whether nodes at other locations receive the message or not. Mobility of nodes is not arbitrary but guarded by a probabilistic mobility function (PMF), and we also define the notion of a weak bisimulation given a PMF. It is possible to have weak bisimular networks which have different probabilistic connectivity information. We furthermore examine the relation between our weak bisimulation and a minor variant of PCTL* [1]. Finally, we apply our calculus on a small example called the Zeroconf protocol [2]
Probabilistic Bisimulation: Naturally on Distributions
In contrast to the usual understanding of probabilistic systems as stochastic
processes, recently these systems have also been regarded as transformers of
probabilities. In this paper, we give a natural definition of strong
bisimulation for probabilistic systems corresponding to this view that treats
probability distributions as first-class citizens. Our definition applies in
the same way to discrete systems as well as to systems with uncountable state
and action spaces. Several examples demonstrate that our definition refines the
understanding of behavioural equivalences of probabilistic systems. In
particular, it solves a long-standing open problem concerning the
representation of memoryless continuous time by memory-full continuous time.
Finally, we give algorithms for computing this bisimulation not only for finite
but also for classes of uncountably infinite systems
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