667 research outputs found
A survey of petri nets slicing
Petri nets slicing is a technique that aims to improve the verification of systems modeled in Petri nets. Petri nets slicing was first developed to facilitate debugging but then used for the alleviation of the state space explosion problem for the model checking of Petri nets. In this article, different slicing techniques are studied along with their algorithms introducing: i) a classification of Petri nets slicing algorithms based on their construction methodology and objective (such as improving state space analysis or testing), ii) a qualitative and quantitative discussion and comparison of major differences such as accuracy and efficiency, iii) a syntactic unification of slicing algorithms that improve state space analysis for easy and clear understanding, and iv) applications of slicing for multiple perspectives. Furthermore, some recent improvements to slicing algorithms are presented, which can certainly reduce the slice size even for strongly connected nets. A noteworthy use of this survey is for the selection and improvement of slicing techniques for optimizing the verification of state event models
Maximal and minimal dynamic Petri net slicing
Context: Petri net slicing is a technique to reduce the size of a Petri net
so that it can ease the analysis or understanding of the original Petri net.
Objective: Presenting two new Petri net slicing algorithms to isolate those
places and transitions of a Petri net (the slice) that may contribute tokens to
one or more places given (the slicing criterion).
Method: The two algorithms proposed are formalized. The completeness of the
first algorithm and the minimality of the second algorithm are formally proven.
Both algorithms together with other three state-of-the-art algorithms have been
implemented and integrated into a single tool so that we have been able to
carry out a fair empirical evaluation.
Results: Besides the two new Petri net slicing algorithms, a public, free,
and open-source implementation of five algorithms is reported. The results of
an empirical evaluation of the new algorithms and the slices that they produce
are also presented.
Conclusions: The first algorithm collects all places and transitions that may
influence (in any computation) the slicing criterion, while the second
algorithm collects a minimum set of places and transitions that may influence
(in some computation) the slicing criterion. Therefore, the net computed by the
first algorithm can reproduce any computation that contributes tokens to any
place of interest. In contrast, the second algorithm loses this possibility but
it often produces a much more reduced subnet (which still can reproduce some
computations that contribute tokens to some places of interest). The first
algorithm is proven complete, and the second one is proven minimal
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
Program Dependence Net and On-demand Slicing for Property Verification of Concurrent System and Software
When checking concurrent software using a finite-state model, we face a
formidable state explosion problem. One solution to this problem is
dependence-based program slicing, whose use can effectively reduce verification
time. It is orthogonal to other model-checking reduction techniques. However,
when slicing concurrent programs for model checking, there are conversions
between multiple irreplaceable models, and dependencies need to be found for
variables irrelevant to the verified property, which results in redundant
computation. To resolve this issue, we propose a Program Dependence Net (PDNet)
based on Petri net theory. It is a unified model that combines a control-flow
structure with dependencies to avoid conversions. For reduction, we present a
PDNet slicing method to capture the relevant variables' dependencies when
needed. PDNet in verifying linear temporal logic and its on-demand slicing can
be used to significantly reduce computation cost. We implement a model-checking
tool based on PDNet and its on-demand slicing, and validate the advantages of
our proposed methods.Comment: 17 pages, 3 figure
Towards a Layered Architectural View for Security Analysis in SCADA Systems
Supervisory Control and Data Acquisition (SCADA) systems support and control
the operation of many critical infrastructures that our society depend on, such
as power grids. Since SCADA systems become a target for cyber attacks and the
potential impact of a successful attack could lead to disastrous consequences
in the physical world, ensuring the security of these systems is of vital
importance. A fundamental prerequisite to securing a SCADA system is a clear
understanding and a consistent view of its architecture. However, because of
the complexity and scale of SCADA systems, this is challenging to acquire. In
this paper, we propose a layered architectural view for SCADA systems, which
aims at building a common ground among stakeholders and supporting the
implementation of security analysis. In order to manage the complexity and
scale, we define four interrelated architectural layers, and uses the concept
of viewpoints to focus on a subset of the system. We indicate the applicability
of our approach in the context of SCADA system security analysis.Comment: 7 pages, 4 figure
Analysis Techniques for Concurrent Programming Languages
Los lenguajes concurrentes est an cada d a m as presentes en nuestra sociedad,
tanto en las nuevas tecnolog as como en los sistemas utilizados de manera cotidiana. M as a un, dada la actual distribuci on de los sistemas y su arquitectura interna,
cabe esperar que este hecho siga siendo una realidad en los pr oximos a~nos. En
este contexto, el desarrollo de herramientas de apoyo al desarrollo de programas
concurrentes se vuelve esencial. Adem as, el comportamiento de los sistemas concurrentes es especialmente dif cil de analizar, por lo que cualquier herramienta que
ayude en esta tarea, a un cuando sea limitada, ser a de gran utilidad. Por ejemplo, podemos encontrar herramientas para la depuraci on, an alisis, comprobaci on,
optimizaci on, o simpli caci on de programas. Muchas de ellas son ampliamente
utilizadas por los programadores hoy en d a.
El prop osito de esta tesis es introducir, a trav es de diferentes lenguajes de
programaci on concurrentes, t ecnicas de an alisis que puedan ayudar a mejorar la
experiencia del desarrollo y publicaci on de software para modelos concurrentes.
En esta tesis se introducen tanto an alisis est aticos (aproximando todas las posibles ejecuciones) como din amicos (considerando una ejecuci on en concreto). Los
trabajos aqu propuestos di eren lo su ciente entre s para constituir ideas totalmente independientes, pero manteniendo un nexo com un: el hecho de ser un
an alisis para un lenguaje concurrente. Todos los an alisis presentados han sido
de nidos formalmente y se ha probado su correcci on, asegurando que los resultados obtenidos tendr an el grado de abilidad necesario en sistemas que lo requieran,
como por ejemplo, en sistemas cr ticos. Adem as, se incluye la descripci on de las
herramientas software que implementan las diferentes ideas propuestas. Esto le da
al trabajo una utilidad m as all a del marco te orico, permitiendo poner en pr actica
y probar con ejemplos reales los diferentes an alisis.
Todas las ideas aqu presentadas constituyen, por s mismas, propuestas aplicables en multitud de contextos y problemas actuales. Adem as, individualmente sirven de punto de partida para otros an alisis derivados, as como para la adaptaci on
a otros lenguajes de la misma familia. Esto le da un valor a~nadido a este trabajo,
como bien atestiguan algunos trabajos posteriores que ya se est an bene ciando de
los resultados obtenidos en esta tesis.Concurrent languages are increasingly present in our society, both in new
technologies and in the systems used on a daily basis. Moreover, given the
current systems distribution and their internal architecture, one can expect
that this remains so in the coming years. In this context, the development of
tools to support the implementation of concurrent programs becomes essential.
Futhermore, the behavior of concurrent systems is particularly difficult
to analyse, so that any tool that helps in this task, even if in a limited way,
will be very useful. For example, one can find tools for debugging, analysis,
testing, optimisation, or simplification of programs, which are widely used
by programmers nowadays.
The purpose of this thesis is to introduce, through various concurrent programming
languages, some analysis techniques that can help to improve the
experience of the software development and release for concurrent models.
This thesis introduces both static (approximating all possible executions) and
dynamic (considering a specific execution) analysis. The topics considered
here differ enough from each other to be fully independent. Nevertheless,
they have a common link: they can be used to analyse properties of a concurrent
programming language. All the analyses presented here have been
formally defined and their correctness have been proved, ensuring that the
results will have the reliability degree which is needed for some systems (for
instance, for critical systems). It also includes a description of the software
tools that implement the different ideas proposed. This gives the work a usefulness
well beyond the theoretical aspect, allowing us to put it in practice
and to test the different analyses with real-world examples All the ideas here presented are, by themselves, approaches that can be applied
in many current contexts and problems. Moreover, individually they
serve as a starting point for other derived analysis, as well as for the adaptation
to other languages of the same family. This gives an added value to
this work, a fact confirmed by some later works that are already benefiting
from the results obtained in this thesis.Tamarit Muñoz, S. (2013). Analysis Techniques for Concurrent Programming Languages [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/31651TESI
Platform Dependent Verification: On Engineering Verification Tools for 21st Century
The paper overviews recent developments in platform-dependent explicit-state
LTL model checking.Comment: In Proceedings PDMC 2011, arXiv:1111.006
Assessing the Risk of an Adaptation using Prior Compliance Verification
Autonomous systems must respond to large amounts of streaming information. They also must comply with critical properties to maintain behavior guarantees. Compliance is especially important when a system self-adapts to perform a repair, improve performance, or modify decisions. There remain significant challenges assessing the risk of adaptations that are dynamically configured at runtime with respect to critical property compliance. Assuming compliance verification was performed for the originally deployed system, the proof process holds valuable meta-data about the variables and conditions that impact reusing the proof on the adapted system. We express this meta-data as a verification workflow using Colored Petri Nets. As dynamic adaptations are configured, the Petri Nets produce alert tokens suggesting the potential proof reuse impact of an adaptation. Alert tokens hold risk values for use in a utility function to determine the least risky adaptations. We illustrate the modeling and risk assessment using a case study
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