The Experts below are selected from a list of 36666 Experts worldwide ranked by ideXlab platform
Jane Hillston - One of the best experts on this subject based on the ideXlab platform.
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probabilistic programming Process Algebra
Quantitative Evaluation of Systems, 2014Co-Authors: Anastasis Georgoulas, Jane Hillston, Dimitrios Milios, Guido SanguinettiAbstract:Formal modelling languages such as Process Algebras are widespread and effective tools in computational modelling. However, handling data and uncertainty in a statistically meaningful way is an open problem in formal modelling, severely hampering the usefulness of these elegant tools in many real world applications. Here we introduce ProPPA, a Process Algebra which incorporates uncertainty in the model description, allowing the use of Machine Learning techniques to incorporate observational information in the modelling. We define the semantics of the language by introducing a quantitative generalisation of Constraint Markov Chains. We present results from a prototype implementation of the language, demonstrating its usefulness in performing inference in a non-trivial example.
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paloma a Process Algebra for located markovian agents
Quantitative Evaluation of Systems, 2014Co-Authors: Cheng Feng, Jane HillstonAbstract:We present a novel stochastic Process Algebra that allows the expression of models representing systems comprised of populations of agents distributed over space, where the relative positions of agents influence their interaction. This language, PALOMA, is given both discrete and continuous semantics and it captures multi-class, multi-message Markovian agent models (M2MAM). Here we present the definition of the language and both forms of semantics, and demonstrate the use of the language to model a flu epidemic under various quarantine regimes.
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numerically representing stochastic Process Algebra models
The Computer Journal, 2012Co-Authors: Jie Ding, Jane HillstonAbstract:Stochastic Process Algebras combine a high-level system description in terms of interacting components, with a rigorous low-level mathematical model in terms of a stochastic Process. These have proved to be valuable modelling formalisms, particularly in the areas of performance modelling and systems biology. However, they do suffer from the problem of state space explosion. Currently, the underlying stochastic Process is generally derived via the small step operational semantics of the Process Algebra and relies on a syntactical representation of the states of the Process. In this paper, we propose a numerical representation schema based on a counting abstraction. This automatically detects symmetries within the state space based on replicated components, and produces a compact state space. Moreover, as we demonstrate, it is amenable to other interpretations and thus other forms of computational analysis, enriching the set of qualitative and quantitative measures that can be derived from a model.
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fluid rewards for a stochastic Process Algebra
IEEE Transactions on Software Engineering, 2012Co-Authors: Mirco Tribastone, Stephen Gilmore, Jie Ding, Jane HillstonAbstract:Reasoning about the performance of models of software systems typically entails the derivation of metrics such as throughput, utilization, and response time. If the model is a Markov chain, these are expressed as real functions of the chain, called reward models. The computational complexity of reward-based metrics is of the same order as the solution of the Markov chain, making the analysis infeasible when evaluating large-scale systems. In the context of the stochastic Process Algebra PEPA, the underlying continuous-time Markov chain has been shown to admit a deterministic (fluid) approximation as a solution of an ordinary differential equation, which effectively circumvents state-space explosion. This paper is concerned with approximating Markovian reward models for PEPA with fluid rewards, i.e., functions of the solution of the differential equation problem. It shows that (1) the Markovian reward models for typical metrics of performance enjoy asymptotic convergence to their fluid analogues, and that (2) via numerical tests, the approximation yields satisfactory accuracy in practice.
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scalable differential analysis of Process Algebra models
IEEE Transactions on Software Engineering, 2012Co-Authors: Mirco Tribastone, Stephen Gilmore, Jane HillstonAbstract:The exact performance analysis of large-scale software systems with discrete-state approaches is difficult because of the well-known problem of state-space explosion. This paper considers this problem with regard to the stochastic Process Algebra PEPA, presenting a deterministic approximation to the underlying Markov chain model based on ordinary differential equations. The accuracy of the approximation is assessed by means of a substantial case study of a distributed multithreaded application.
Peter Höfner - One of the best experts on this subject based on the ideXlab platform.
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a Process Algebra for link layer protocols
arXiv: Networking and Internet Architecture, 2019Co-Authors: Peter Höfner, Rob Van Glabbeek, Michael MarklAbstract:We propose a Process Algebra for link layer protocols, featuring a unique mechanism for modelling frame collisions. We also formalise suitable liveness properties for link layer protocols specified in this framework. To show applicability we model and analyse two versions of the Carrier-Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol. Our analysis confirms the hidden station problem for the version without virtual carrier sensing. However, we show that the version with virtual carrier sensing not only overcomes this problem, but also the exposed station problem with probability 1. Yet the protocol cannot guarantee packet delivery, not even with probability 1.
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a timed Process Algebra for wireless networks with an application in routing
European Symposium on Programming, 2016Co-Authors: Emile Bres, Rob Van Glabbeek, Peter HöfnerAbstract:This paper proposes a timed Process Algebra for wireless networks, an extension of the Algebra for Wireless Networks. It combines treatments of local broadcast, conditional unicast and data structures, which are essential features for the modelling of network protocols. In this framework we model and analyse the Ad hoc On-Demand Distance Vector routing protocol, and show that, contrary to claims in the literature, it fails to be loop free. We also present boundary conditions for a fix ensuring that the resulting protocol is indeed loop free.
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Mechanizing a Process Algebra for Network Protocols
Journal of Automated Reasoning, 2016Co-Authors: Timothy Bourke, Robert Van Glabbeek, Peter HöfnerAbstract:This paper presents the mechanization of a Process Algebra for Mobile Ad hoc Networks and Wireless Mesh Networks, and the development of a compositional framework for proving invariant properties. Mechanizing the core Process Algebra in Isabelle/HOL is relatively standard, but its layered structure necessitates special treatment. The control states of reactive Processes, such as nodes in a network, are modelled by terms of the Process Algebra. We propose a technique based on these terms to streamline proofs of inductive invariance. This is not sufficient, however, to state and prove invariants that relate states across multiple Processes (entire networks). To this end, we propose a novel composi-tional technique for lifting global invariants stated at the level of individual nodes to networks of nodes.
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a Process Algebra for wireless mesh networks
arXiv: Logic in Computer Science, 2015Co-Authors: Ansgar Fehnker, Peter Höfner, Rob Van Glabbeek, Annabelle Mciver, Marius Portmann, Wee Lum TanAbstract:We propose a Process Algebra for wireless mesh networks that combines novel treatments of local broadcast, conditional unicast and data structures. In this framework, we model the Ad-hoc On-Demand Distance Vector (AODV) routing protocol and (dis)prove crucial properties such as loop freedom and packet delivery.
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Showing Invariance Compositionally for a Process Algebra for Network Protocols
2014Co-Authors: Timothy Bourke, Robert Van Glabbeek, Peter HöfnerAbstract:This paper presents the mechanization of a Process Algebra for Mobile Ad hoc Networks and Wireless Mesh Networks, and the development of a compositional framework for proving invariant properties. Mechanizing the core Process Algebra in Isabelle/HOL is relatively standard, but its layered structure necessitates special treatment. The control states of reactive Processes, such as nodes in a network, are modelled by terms of the Process Algebra. We propose a technique based on these terms to streamline proofs of inductive invariance. This is not sufficient, however, to state and prove invariants that relate states across multiple Processes (entire networks). To this end, we propose a novel compositional technique for lifting global invariants stated at the level of individual nodes to networks of nodes.
Rob Van Glabbeek - One of the best experts on this subject based on the ideXlab platform.
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reactive bisimulation semantics for a Process Algebra with time outs
arXiv: Logic in Computer Science, 2020Co-Authors: Rob Van GlabbeekAbstract:This paper introduces the counterpart of strong bisimilarity for labelled transition systems extended with time-out transitions. It supports this concept through a modal characterisation, congruence results for a standard Process Algebra with recursion, and a complete axiomatisation.
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failure trace semantics for a Process Algebra with time outs
arXiv: Logic in Computer Science, 2020Co-Authors: Rob Van GlabbeekAbstract:This paper extends a standard Process Algebra with a time-out operator, thereby increasing its absolute expressiveness, while remaining within the realm of untimed Process Algebra, in the sense that the progress of time is not quantified. Trace and failures equivalence fail to be congruences for this operator; their congruence closure is characterised as failure trace equivalence.
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a Process Algebra for link layer protocols
arXiv: Networking and Internet Architecture, 2019Co-Authors: Peter Höfner, Rob Van Glabbeek, Michael MarklAbstract:We propose a Process Algebra for link layer protocols, featuring a unique mechanism for modelling frame collisions. We also formalise suitable liveness properties for link layer protocols specified in this framework. To show applicability we model and analyse two versions of the Carrier-Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol. Our analysis confirms the hidden station problem for the version without virtual carrier sensing. However, we show that the version with virtual carrier sensing not only overcomes this problem, but also the exposed station problem with probability 1. Yet the protocol cannot guarantee packet delivery, not even with probability 1.
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a timed Process Algebra for wireless networks with an application in routing
European Symposium on Programming, 2016Co-Authors: Emile Bres, Rob Van Glabbeek, Peter HöfnerAbstract:This paper proposes a timed Process Algebra for wireless networks, an extension of the Algebra for Wireless Networks. It combines treatments of local broadcast, conditional unicast and data structures, which are essential features for the modelling of network protocols. In this framework we model and analyse the Ad hoc On-Demand Distance Vector routing protocol, and show that, contrary to claims in the literature, it fails to be loop free. We also present boundary conditions for a fix ensuring that the resulting protocol is indeed loop free.
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a Process Algebra for wireless mesh networks
arXiv: Logic in Computer Science, 2015Co-Authors: Ansgar Fehnker, Peter Höfner, Rob Van Glabbeek, Annabelle Mciver, Marius Portmann, Wee Lum TanAbstract:We propose a Process Algebra for wireless mesh networks that combines novel treatments of local broadcast, conditional unicast and data structures. In this framework, we model the Ad-hoc On-Demand Distance Vector (AODV) routing protocol and (dis)prove crucial properties such as loop freedom and packet delivery.
Gwen Salaün - One of the best experts on this subject based on the ideXlab platform.
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Realizability of Choreographies using Process Algebra Encodings
IEEE Transactions on Services Computing, 2012Co-Authors: Gwen Salaün, Tevfik Bultan, Nima RoohiAbstract:Service-oriented computing has emerged as a new software development paradigm that enables implementation of Web accessible software systems that are composed of distributed services which interact with each other via exchanging messages. Modeling and analysis of interactions among services is a crucial problem in this domain. Interactions among a set of services that participate in a service composition can be described from a global point of view as a choreography. Choreographies can be specified using specification languages such as Web Services Choreography Description Language (WS-CDL) and visualized using graphical formalisms such as collaboration diagrams. In this article, we present an encoding of collaboration diagrams into the LOTOS Process Algebra for choreography analysis. This encoding allows us to (i) check the temporal properties of choreographies using a LOTOS verification tool set called the Construction and Analysis of Distributed Processes (CADP) toolbox, (ii) check the realizability of choreographies for both synchronous communication and bounded asynchronous communication, and (iii) automate the peer generation Process. Realizability indicates whether peers can be generated from a given choreography specification in such a way that the interactions of the generated peers exactly match the choreography specification. If a collaboration diagram is unrealizable, our approach extends the peer generation Process by adding extra communication that guarantees that the peers behave according to the choreography specification.
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realizability of choreographies using Process Algebra encodings
Integrated Formal Methods, 2009Co-Authors: Gwen Salaün, Tevfik BultanAbstract:Service-oriented computing has emerged as a new programming paradigm that aims at implementing software applications which can be used through a network via the exchange of messages. Interactions among a set of services involved in a new system are described from a global point of view using choreography specification languages such as WS-CDL or collaboration diagrams. In this paper, we present an encoding of collaboration diagrams into the LOTOS Process Algebra. This encoding allows to (i) check choreography specification using the LOTOS verification toolbox (CADP), (ii) check realizability of collaboration diagrams for both synchronous communication and bounded asynchronous communication, and (iii) automate service peer generation. Realizability indicates whether peers can be generated from a choreography such that they will behave exactly as formalized in its specification. If the collaboration diagram is unrealizable, our approach extends the peer generation Process by adding some communications that make the peers respect the choreography specification.
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behavioral adaptation of component compositions based on Process Algebra encodings
Automated Software Engineering, 2007Co-Authors: Radu Mateescu, Pascal Poizat, Gwen SalaünAbstract:Software adaptation has been proposed as a solution to mismatch between components through the generation of software pieces called adaptors. We propose a new behavioral adaptation approach for the generation of adaptor protocols. Compared to related work, it is fully automated and addresses the adaptor computation complexity thanks to Process Algebra encodings and on-the-fly techniques.
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describing and reasoning on web services using Process Algebra
International Conference on Web Services, 2004Co-Authors: Gwen Salaün, Lucas Bordeaux, Marco SchaerfAbstract:We argue that essential facets of Web services, and especially those useful to understand their interaction, can be described using Process-Algebraic notations. Web service description and execution languages such as BPEL are essentially Process description languages; they are based on primitives for behaviour description and message exchange which can also be found in more abstract Process Algebras. One legitimate question is therefore whether the formal approach and the sophisticated tools introduced for Process Algebra can be used to improve the effectiveness and the reliability of Web service development. Our investigations suggest a positive answer, and we claim that Process Algebras provide a very complete and satisfactory assistance to the whole Process of Web service development. We show on a case study that readily available tools based on Process Algebra are effective at verifying that Web services conform to their requirements and respect properties. We advocate their use both at the design stage and for reverse engineering issues. More prospectively, we discuss how they can be helpful to tackle choreography issues.
Mirco Tribastone - One of the best experts on this subject based on the ideXlab platform.
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differential bisimulation for a markovian Process Algebra
Mathematical Foundations of Computer Science, 2015Co-Authors: Giulio Iacobelli, Mirco Tribastone, Andrea VandinAbstract:Formal languages with semantics based on ordinary differential equations (ODEs) have emerged as a useful tool to reason about large-scale distributed systems. We present differential bisimulation, a behavioral equivalence developed as the ODE counterpart of bisimulations for languages with probabilistic or stochastic semantics. We study it in the context of a Markovian Process Algebra. Similarly to Markovian bisimulations yielding an aggregated Markov Process in the sense of the theory of lumpability, differential bisimulation yields a partition of the ODEs underlying a Process Algebra term, whereby the sum of the ODE solutions of the same partition block is equal to the solution of a single (lumped) ODE. Differential bisimulation is defined in terms of two symmetries that can be verified only using syntactic checks. This enables the adaptation to a continuous-state semantics of proof techniques and algorithms for finite, discrete-state, labeled transition systems. For instance, we readily obtain a result of compositionality, and provide an efficient partition-refinement algorithm to compute the coarsest ODE aggregation of a model according to differential bisimulation.
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a unified framework for differential aggregations in markovian Process Algebra
The Journal of Logic and Algebraic Programming, 2015Co-Authors: Max Tschaikowski, Mirco TribastoneAbstract:Fluid semantics for Markovian Process Algebra have recently emerged as a computationally attractive approximate way of reasoning about the behaviour of stochastic models of large-scale systems. This interpretation is particularly convenient when sequential components characterised by small local state spaces are present in many independent copies. While the traditional Markovian interpretation causes state-space explosion, fluid semantics is independent from the multiplicities of the sequential components present in the model, just associating a single ordinary differential equation (ODE) with each local state. In this paper we analyse the case of a Process Algebra model inducing a large ODE system. Previous work, known as exact fluid lumpability, requires two symmetries: ODE aggregation is possible for Processes that i) are isomorphic and that ii) are present with the same multiplicities. We first relax the latter requirement by introducing the notion of ordinary fluid lumpability, which yields an ODE system where the sum of the aggregated variables is preserved exactly. Then, we consider approximate variants of both notions of lumpability which make nearby Processes symmetric after a perturbation of their parameters. We prove that small perturbations yield nearby differential trajectories. We carry out our study in the context of a Process Algebra that unifies two synchronisation semantics that are well studied in the literature, useful for the modelling of computer systems and chemical networks, respectively. In both cases, we provide numerical evidence which shows that, in practice, many heterogeneous Processes can be aggregated with negligible errors.
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behavioral relations in a Process Algebra for variants
Software Product Lines, 2014Co-Authors: Mirco TribastoneAbstract:Variant Process Algebra is designed for the formal behavioral modeling of software variation, as arises, for instance, in software product line engineering. Process terms are labelled with the sets of variants, i.e., specific products, where they are enabled. A multi-modal operational semantics enables two compositional forms of reasoning. The first one is concerned with relating the behavior of a variant to the whole family. The second notion relates variants between each other, for instance to be able to formally capture the intuitive idea that a variant is a conservative extension of another, in the sense that it adds more behavior without breaking any existing one. Sufficient conditions are given to establish such a relation statically, by means of syntactic checks on Process terms.
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exact fluid lumpability for markovian Process Algebra
International Conference on Concurrency Theory, 2012Co-Authors: Max Tschaikowski, Mirco TribastoneAbstract:We study behavioural relations for Process Algebra with a fluid semantics given in terms of a system of ordinary differential equations (ODEs). We introduce label equivalence, a relation which is shown to induce an exactly lumped fluid model, a potentially smaller ODE system which can be exactly related to the original one. We show that, in general, for two Processes that are related in the fluid sense nothing can be said about their relationship from stochastic viewpoint. However, we identify a class of models for which label equivalence implies a correspondence, called semi-isomorphism, between their transition systems that are at the basis of the Markovian interpretation.
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fluid rewards for a stochastic Process Algebra
IEEE Transactions on Software Engineering, 2012Co-Authors: Mirco Tribastone, Stephen Gilmore, Jie Ding, Jane HillstonAbstract:Reasoning about the performance of models of software systems typically entails the derivation of metrics such as throughput, utilization, and response time. If the model is a Markov chain, these are expressed as real functions of the chain, called reward models. The computational complexity of reward-based metrics is of the same order as the solution of the Markov chain, making the analysis infeasible when evaluating large-scale systems. In the context of the stochastic Process Algebra PEPA, the underlying continuous-time Markov chain has been shown to admit a deterministic (fluid) approximation as a solution of an ordinary differential equation, which effectively circumvents state-space explosion. This paper is concerned with approximating Markovian reward models for PEPA with fluid rewards, i.e., functions of the solution of the differential equation problem. It shows that (1) the Markovian reward models for typical metrics of performance enjoy asymptotic convergence to their fluid analogues, and that (2) via numerical tests, the approximation yields satisfactory accuracy in practice.
