481 research outputs found
Effective Marking Equivalence Checking in Systems with Dynamic Process Creation
The starting point of this work is a framework allowing to model systems with
dynamic process creation, equipped with a procedure to detect symmetric
executions (ie., which differ only by the identities of processes). This allows
to reduce the state space, potentially to an exponentially smaller size, and,
because process identifiers are never reused, this also allows to reduce to
finite size some infinite state spaces. However, in this approach, the
procedure to detect symmetries does not allow for computationally efficient
algorithms, mainly because each newly computed state has to be compared with
every already reached state.
In this paper, we propose a new approach to detect symmetries in this
framework that will solve this problem, thus enabling for efficient algorithms.
We formalise a canonical representation of states and identify a sufficient
condition on the analysed model that guarantees that every symmetry can be
detected. For the models that do not fall into this category, our approach is
still correct but does not guarantee a maximal reduction of state space.Comment: In Proceedings Infinity 2012, arXiv:1302.310
Semantic Embedding of Petri Nets into Event-B
We present an embedding of Petri nets into B abstract systems. The embedding
is achieved by translating both the static structure (modelling aspect) and the
evolution semantics of Petri nets. The static structure of a Petri-net is
captured within a B abstract system through a graph structure. This abstract
system is then included in another abstract system which captures the evolution
semantics of Petri-nets. The evolution semantics results in some B events
depending on the chosen policies: basic nets or high level Petri nets. The
current embedding enables one to use conjointly Petri nets and Event-B in the
same system development, but at different steps and for various analysis.Comment: 16 pages, 3 figure
Quantitative evaluation of Pandora Temporal Fault Trees via Petri Nets
© 2015, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. Using classical combinatorial fault trees, analysts are able to assess the effects of combinations of failures on system behaviour but are unable to capture sequence dependent dynamic behaviour. Pandora introduces temporal gates and temporal laws to fault trees to allow sequence-dependent dynamic analysis of events. Pandora can be easily integrated in model-based design and analysis techniques; however, the combinatorial quantification techniques used to solve classical fault trees cannot be applied to temporal fault trees. Temporal fault trees capture state and therefore require a state space solution for quantification of probability. In this paper, we identify Petri Nets as a possible framework for quantifying temporal trees. We describe how Pandora fault trees can be mapped to Petri Nets for dynamic dependability analysis and demonstrate the process on a fault tolerant fuel distribution system model
Analysing Coloured Petri Nets by the Occurrence Graph Method
This paper provides an overview og the work done for the author's PhD thesis. The research area of Coloured Petri Nets is introduced, and the available analysis methods are presented. The occurrence graph method, which is the main subject of this thesis, is described in more detail. Summaries of the six papers which, together with this overview, comprise the thesis are given, and the contributions are discussed.A large portion of this overview is dedicated to a description of related work. The aim is twofold: First, to survey pertinent results within the research areas of -- in increasing generality -- Coloured Petri Nets, High-level Petri Nets, and formalisms for modelling and analysis of parallel and distributed systems. Second, to put the results obtained in this thesis in a wider perspective by comparing them with important related work
KReach : a tool for reachability in petri nets
We present KReach, a tool for deciding reachability in general Petri nets. The tool is a full implementation of Kosaraju’s original 1982 decision procedure for reachability in VASS. We believe this to be the first implementation of its kind. We include a comprehensive suite of libraries for development with Vector Addition Systems (with States) in the Haskell programming language. KReach serves as a practical tool, and acts as an effective teaching aid for the theory behind the algorithm. Preliminary tests suggest that there are some classes of Petri nets for which we can quickly show unreachability. In particular, using KReach for coverability problems, by reduction to reachability, is competitive even against state-of-the-art coverability checkers
Towards efficient verification of systems with dynamic process creation
Modelling and analysis of dynamic multi-threaded state systems often encounters obstacles when one wants to use automated verification methods, such as model checking. Our aim in this paper is to develop a technical device for coping with one such obstacle, namely that caused by dynamic process creation. We first introduce a general class of coloured Petri nets-not tied to any particular syntax or approach-allowing one to capture systems with dynamic (and concurrent) process creation as well as capable of manipulating data. Following this, we introduce the central notion of our method which is a marking equivalence that can be efficiently computed and then used, for instance, to aggregate markings in a reachability graph. In some situations, such an aggregation may produce a finite representation of an infinite state system which still allows one to establish the relevant behavioural properties. We show feasibility of the method on an example and provide initial experimental results
Representing Conversations for Scalable Overhearing
Open distributed multi-agent systems are gaining interest in the academic
community and in industry. In such open settings, agents are often coordinated
using standardized agent conversation protocols. The representation of such
protocols (for analysis, validation, monitoring, etc) is an important aspect of
multi-agent applications. Recently, Petri nets have been shown to be an
interesting approach to such representation, and radically different approaches
using Petri nets have been proposed. However, their relative strengths and
weaknesses have not been examined. Moreover, their scalability and suitability
for different tasks have not been addressed. This paper addresses both these
challenges. First, we analyze existing Petri net representations in terms of
their scalability and appropriateness for overhearing, an important task in
monitoring open multi-agent systems. Then, building on the insights gained, we
introduce a novel representation using Colored Petri nets that explicitly
represent legal joint conversation states and messages. This representation
approach offers significant improvements in scalability and is particularly
suitable for overhearing. Furthermore, we show that this new representation
offers a comprehensive coverage of all conversation features of FIPA
conversation standards. We also present a procedure for transforming AUML
conversation protocol diagrams (a standard human-readable representation), to
our Colored Petri net representation
Parallel symbolic state-space exploration is difficult, but what is the alternative?
State-space exploration is an essential step in many modeling and analysis
problems. Its goal is to find the states reachable from the initial state of a
discrete-state model described. The state space can used to answer important
questions, e.g., "Is there a dead state?" and "Can N become negative?", or as a
starting point for sophisticated investigations expressed in temporal logic.
Unfortunately, the state space is often so large that ordinary explicit data
structures and sequential algorithms cannot cope, prompting the exploration of
(1) parallel approaches using multiple processors, from simple workstation
networks to shared-memory supercomputers, to satisfy large memory and runtime
requirements and (2) symbolic approaches using decision diagrams to encode the
large structured sets and relations manipulated during state-space generation.
Both approaches have merits and limitations. Parallel explicit state-space
generation is challenging, but almost linear speedup can be achieved; however,
the analysis is ultimately limited by the memory and processors available.
Symbolic methods are a heuristic that can efficiently encode many, but not all,
functions over a structured and exponentially large domain; here the pitfalls
are subtler: their performance varies widely depending on the class of decision
diagram chosen, the state variable order, and obscure algorithmic parameters.
As symbolic approaches are often much more efficient than explicit ones for
many practical models, we argue for the need to parallelize symbolic
state-space generation algorithms, so that we can realize the advantage of both
approaches. This is a challenging endeavor, as the most efficient symbolic
algorithm, Saturation, is inherently sequential. We conclude by discussing
challenges, efforts, and promising directions toward this goal
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