5,492 research outputs found
Reachability of Communicating Timed Processes
We study the reachability problem for communicating timed processes, both in
discrete and dense time. Our model comprises automata with local timing
constraints communicating over unbounded FIFO channels. Each automaton can only
access its set of local clocks; all clocks evolve at the same rate. Our main
contribution is a complete characterization of decidable and undecidable
communication topologies, for both discrete and dense time. We also obtain
complexity results, by showing that communicating timed processes are at least
as hard as Petri nets; in the discrete time, we also show equivalence with
Petri nets. Our results follow from mutual topology-preserving reductions
between timed automata and (untimed) counter automata.Comment: Extended versio
Recommended from our members
Modeling and analysis of concurrent systems
A survey of modeling and analysis techniques in common use for modeling and analyzing concurrent systems. The models surveyed are CSP (Communicating Sequential Processes), Path Expressions, CCS (Calculus of Communicating Systems), CIRCAL, Petri Nets, Coloured Petri Nets, Predicate-Action Nets, Numerical Petri Nets, Contour-Transition Nets, and several varieties of Timed Petri Nets. The analysis techniques are state-space analysis, temporal logic, structural analysis, and inductive analysis
Preemptive D-timed Petri nets, timeouts, modeling and analysis of communication protocols
Preemptive D-timed Petri nets are Petri nets with deterministic firing times and with generalized inhibitor arcs to interrupt firing transitions. A formalism is presented which represents the behavior of free-choice D-timed Petri nets by discrete-space discrete-time semi-Markov processes. Stationary probabilities of states can thus be determined by standard techniques used for analysis of Markov chains. A straightforward application of timed Petri nets is modelling and analysis of systems of asynchronous communicating processes, and in particular communication protocols. Places of Petri nets model queues of messages, transitions represent delays in communication networks, interrupt arcs conveniently model timeout mechanisms, and probabilities associated with free-choice classes correspond to relative frequencies of random events. Simple protocols are used as an illustration of modelling and analysis
M-timed Petri nets, priorities, preemptions, and performance evaluation of systems
In M-timed Petri nets, firing times are exponentially distributed random variables associated with transitions of a net. Several classes of M-timed Petri nets are discussed in this paper to show increasing âmodelling powerâ of different nets. Conflict-free nets can model M- and E k -type queueing systems. Free-choice nets can also represent H k -type systems. Systems with several classes of users and with service priorities assigned to user classes require nets with inhibitor arcs. Preemption of service can be represented by extended nets with escape (or generalized inhibitor) arcs. Finally, to provide flexible modelling of scheduling and decision strategies, enhanced Petri nets are introduced with two classes of transitions, immediate and timed ones, and with (exponentially distributed) firing times associated with the timed transitions. It is shown that the behavior of bounded M-timed Petri nets can be represented by finite âstateâ graphs which are finite-state continuous-time homogeneous Markov processes. Stationary probabilities of states can thus be obtained by standard techniques used for analysis of Markov chains, and then operational analysis can be applied for performance evaluation. Simple models of interactive systems are used as an illustration of modelling
Timed Basic Parallel Processes
Timed basic parallel processes (TBPP) extend communication-free Petri nets (aka. BPP or commutative context-free grammars) by a global notion of time. TBPP can be seen as an extension of timed automata (TA) with context-free branching rules, and as such may be used to model networks of independent timed automata with process creation. We show that the coverability and reachability problems (with unary encoded target multiplicities) are PSPACE-complete and EXPTIME-complete, respectively. For the special case of 1-clock TBPP, both are NP-complete and hence not more complex than for untimed BPP. This contrasts with known super-Ackermannian-completeness and undecidability results for general timed Petri nets. As a result of independent interest, and basis for our NP upper bounds, we show that the reachability relation of 1-clock TA can be expressed by a formula of polynomial size in the existential fragment of linear arithmetic, which improves on recent results from the literature
Modified D-timed Petri nets, timeouts, and modelling of communication protocols
Modified D-timed Petri nets are Petri nets with âspe-
cialâ arcs to interrupt firing transitions, and with deter-
ministic firing times; these special arcs are called âin-
terruptâ arcs. It is shown that the behaviour of simple
modified bounded free-choice D-timed Petri nets can be
represented by finite probabilistic state graphs, stationary
probabilities of states can thus be obtained by standard
techniques used for analysis of Markov chains. An imme-
diate application of such a model is performance analysis
of systems of interacting asynchronous processes, and in
particular communication protocols. Places of Petri nets
model queues of messages, transitions represent events
in communication networks, interrupt arcs conveniently
model timeouts, and probabilities associated with free-
choice classes correspond to relative frequencies of random events. A simple protocol based on unnumbered messages and acknowledgements is used as an illustration of analy-
sis
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
Modeling and analysis of semiconductor manufacturing processes using petri nets
This thesis addresses the issues in modeling and analysis of multichip module (MCM) manufacturing processes using Petri nets. Building such graphical and mathematical models is a crucial step to understand MCM technologies and to enhance their application scope.
In this thesis, the application of Petri nets is presented with top-down and bottom-up approaches. The theory of Petri nets is summarized with its basic notations and properties at first. After that, the capability of calculating and analyzing Petri nets with deterministic timing information is extended to meet the requirements of the MCM models. Then, using top-down refining and system decomposition, MCM models are built from an abstract point to concrete systems with timing information. In this process, reduction theory based on a multiple-input-single-output modules for deterministic Petri nets is applied to analyze the cycle time of Petri net models. Besides, this thesis is of significance in its use of the reduction theory which is derived for timed marked graphs - an important class of Petri nets
Towards a Notion of Distributed Time for Petri Nets
We set the ground for research on a timed extension of Petri nets where time parameters are associated with tokens and arcs carry constraints that qualify the age of tokens required for enabling. The novelty is that, rather than a single global clock, we use a set of unrelated clocks --- possibly one per place --- allowing a local timing as well as distributed time synchronisation. We give a formal definition of the model and investigate properties of local versus global timing, including decidability issues and notions of processes of the respective models
Extending the Petri box calculus with time
PBC (Petri Box Calculus) is a process algebra where real parallelism of concurrent systems can be naturally expressed. One of its main features is the definition of a denotational semantics based on Petri nets, which emphasizes the structural aspects of the modelled systems. However, this formal model does not include temporal aspects of processes, which are necessary when considering real-time systems. The aim of this paper is to extend the existing calculus with those temporal aspects. We consider that actions are not instantaneous, that is, their execution takes time. We present an operational semantics and a denotational semantics based on timed Petri nets. Finally, we discuss the introduction of other new features such as time-outs and delays. Throughout the paper we assume that the reader is familiar with both Petri nets and PBC
- âŠ