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32
Process Algebra for Performance Evaluation
, 2000
"... This paper surveys the theoretical developments in the field of stochastic process algebras, process algebras where action occurrences may be subject to a delay that is determined by a random variable. A huge class of resourcesharing systems  like largescale computers, clientserver architectur ..."
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Cited by 71 (13 self)
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This paper surveys the theoretical developments in the field of stochastic process algebras, process algebras where action occurrences may be subject to a delay that is determined by a random variable. A huge class of resourcesharing systems  like largescale computers, clientserver architectures, networks  can accurately be described using such stochastic specification formalisms.
The Theory of Interactive Generalized SemiMarkov Processes
 Theoretical Computer Science
, 2000
"... In this paper we introduce the calculus of Interactive Generalized SemiMarkov Processes (IGSMPs), a stochastic process algebra which can express probabilistic timed delays with general distributions and synchronizable actions with zero duration, and where choices may be probabilistic, nondetermini ..."
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Cited by 36 (7 self)
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In this paper we introduce the calculus of Interactive Generalized SemiMarkov Processes (IGSMPs), a stochastic process algebra which can express probabilistic timed delays with general distributions and synchronizable actions with zero duration, and where choices may be probabilistic, nondeterministic and prioritized. IGSMP is equipped with a structural operational semantics which generates semantic models in the form of Generalized SemiMarkov Processes (GSMPs), i.e. probabilistic systems with generally distributed time, extended with action transitions representing interaction among system components. This is obtained by expressing the concurrent execution of delays through a variant of ST semantics which is based on dynamic names. The fact that names for delays are generated dynamically by the semantics makes it possible to dene a notion of observational congruence for IGSMP (that abstracts from internal actions with zero duration) simply as a combination of standard observatio...
Compositional Asymmetric Cooperations for Process Algebras with Probabilities, Priorities, and Time
, 2000
"... The modeling and analysis experience with process algebras has shown the necessity of extending them with priority, probabilistic internal/external choice, and time in order to be able to faithfully model the behavior of real systems and capture the properties of interest. An important open problem ..."
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Cited by 29 (17 self)
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The modeling and analysis experience with process algebras has shown the necessity of extending them with priority, probabilistic internal/external choice, and time in order to be able to faithfully model the behavior of real systems and capture the properties of interest. An important open problem in this scenario is how to obtain semantic compositionality in the presence of all these mechanisms, to allow for an efficient analysis. In this paper we argue that, when abandoning the classical nondeterministic setting by considering the mechanisms above, a natural solution is to break the symmetry of the roles of the processes participating in a synchronization. We accomplish this by distinguishing between master actions – the choice among which is carried out generatively according to their priorities/probabilities or exponentially distributed durations – and slave actions – the choice among which is carried out reactively according to their priorities/probabilities – and by imposing that a master action can synchronize with slave actions only. Technically speaking, in this paper we define a process algebra called EMPAgr including probabilities, priorities, exponentially distributed durations, and the generative masterreactive slaves synchronization mechanism. Then, we prove that the synchronization mechanism in EMPAgr is correct w.r.t. the novel cooperation structure model, we show that the Markovian bisimulation equivalence is a congruence for EMPAgr, and we present a sound and complete axiomatization for finite terms. This paper is electronically published in
Action Refinement
 Handbook of Proacess Algebra
, 2000
"... S. All local authors can be reached via email at the address lastname@cs.unibo.it. Questions and comments should be addressed to tradmin@cs.unibo.it. Recent Titles from the UBLCS Technical Report Series 974 An Algebra of Actors, M. Gaspari, G. Zavattaro, May 1997. 975 On the Turing Equivalen ..."
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Cited by 29 (4 self)
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S. All local authors can be reached via email at the address lastname@cs.unibo.it. Questions and comments should be addressed to tradmin@cs.unibo.it. Recent Titles from the UBLCS Technical Report Series 974 An Algebra of Actors, M. Gaspari, G. Zavattaro, May 1997. 975 On the Turing Equivalence of Linda Coordination Primitives, N. Busi, R. Gorrieri, G. Zavattaro, May 1997 (Revised October 1998). 976 A Process Algebraic View of Linda Coordination Primitives, N. Busi, R. Gorrieri, G. Zavattaro, May 1997. 977 Validating a Software Architecture with respect to an Architectural Style, P. Ciancarini, W. Penzo, July 1997. 978 System Support for PartitionAware Network Applications, O. Babaoglu, R. Davoli, A. Montresor, R. Segala, October 1997. 979 Generalized SemiMarkovian Process Algebra, M. Bravetti, M. Bernardo, R. Gorrieri, October 1997. 981 Group Communication in Partitionable Systems: Specification and Algorithms, O. Babao glu, R. Davoli, A. Montresor, April 1998. 982...
Tutte le algebre insieme: Concepts, discussions and relations of stochastic process algebras with general distributions
 In Validation of Stochastic Systems
, 2004
"... Abstract. We report on the state of the art in the formal specification and analysis of concurrent systems whose activity duration depends on general probability distributions. First of all the basic notions and results introduced in the literature are explained and, on this basis, a conceptual clas ..."
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Cited by 18 (5 self)
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Abstract. We report on the state of the art in the formal specification and analysis of concurrent systems whose activity duration depends on general probability distributions. First of all the basic notions and results introduced in the literature are explained and, on this basis, a conceptual classification of the different approaches is presented. We observe that most of the approaches agree on the fact that the specification of systems with general distributions has a three level structure: the process algebra level, the level of symbolic semantics and the level of concrete semantics. Based on such observations, a new very expressive model is introduced for representing timed systems with general distributions. We show that many of the approaches in the literature can be mapped into this model establishing therefore a formal framework to compare these approaches. 1
Deciding and axiomatizing weak ST bisimulation for a process algebra with recursion and action refinement
 ACM Transactions on Computational Logic
, 2002
"... 1. INTRODUCTION ST semantics, originally defined in [van Glabbeek and Vaandrager 1987] over Petri Nets, is one of the most studied noninterleaving semantics. The main reason is that ST semantics is the less informative semantics that is a congruence for ..."
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Cited by 14 (6 self)
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1. INTRODUCTION ST semantics, originally defined in [van Glabbeek and Vaandrager 1987] over Petri Nets, is one of the most studied noninterleaving semantics. The main reason is that ST semantics is the less informative semantics that is a congruence for
Reliable Performance Modelling with Approximate Synchronisations
 In Process Algebra and Performance Modelling Workshop
, 1999
"... Markovian Process Algebras approximate their model of synchronisation events in order to preserve their Markovian nature. This paper investigates synchronisation models in a stochastic context and focuses on how the Markovian approximation of synchronisation a#ects the accuracy of the performanc ..."
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Cited by 12 (5 self)
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Markovian Process Algebras approximate their model of synchronisation events in order to preserve their Markovian nature. This paper investigates synchronisation models in a stochastic context and focuses on how the Markovian approximation of synchronisation a#ects the accuracy of the performance model. TIPP and PEPA are used as speci#c cases throughout, and their di#erent methods of synchronisation are compared for e#ectiveness in performance modelling. The paper ends with a generally distributed example of realworld synchronisation, whichwe are able to solve analytically and then approximately with four Markovian Process Algebra models. From the results of this analysis, we are able to suggest other Markovian synchronisation models which complement and improve on those presented by TIPP and PEPA.
Towards Reliable Modelling with Stochastic Process Algebras
 Department of Computer Science, University of Bristol, Bristol
, 1999
"... Abstract In this thesis, we investigate reliable modelling within a stochastic process algebra framework. Primarily, we consider issues of variance in stochastic process algebras as a measure of model reliability. This is in contrast to previous research in the field which has tended to centre aroun ..."
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Cited by 11 (6 self)
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Abstract In this thesis, we investigate reliable modelling within a stochastic process algebra framework. Primarily, we consider issues of variance in stochastic process algebras as a measure of model reliability. This is in contrast to previous research in the field which has tended to centre around mean behaviour and steadystate solutions. We present a method of stochastic aggregation for analysing generallydistributed processes. This allows us more descriptive power in representing stochastic systems and thus gives us the ability to create more accurate models. We improve upon two welldeveloped Markovian process algebras and show how their simpler paradigm can be brought to bear on more realistic synchronisation models. Now, reliable performance figures can be obtained for systems, where previously only approximations of unknown accuracy were possible. Finally, we describe reliability definitions and variance metrics in stochastic models and demonstrate how systems can be made more reliable through careful combination under stochastic process algebra operators. ii Acknowledgements My three years in the department in Bristol have been a lot of fun and the person I have most to thank for this is my friend and mentor, Neil Davies. I should also acknowledge the funding from NATS for my project and especially the help of Suresh Tewari (NATS) and Gordon Hughes (SSRC).
Specification and analysis of soft realtime systems: quantity and quality
 In: RTSS’99
, 1999
"... This paper presents a process algebra for specifying soft realtime constraints in a compositional way. For these soft constraints we take a stochastic point of view and allow arbitrary probability distributions to express delays of activities. The semantics of this process algebra is given in terms ..."
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Cited by 11 (4 self)
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This paper presents a process algebra for specifying soft realtime constraints in a compositional way. For these soft constraints we take a stochastic point of view and allow arbitrary probability distributions to express delays of activities. The semantics of this process algebra is given in terms of stochastic automata, a variant of timed automata where clocks are initialised randomly and run backwards. To analyse quantitative properties, an algorithm is presented for the onthefly generation of a discreteevent simulation model from a process algebra specification. On the qualitative side, a symbolic technique for classical reachability analysis of stochastic automata is presented. As a result a unifying framework for the specification and analysis of quantitative and qualitative properties is obtained. We discuss an implementation of both analytic methods and specify and analyse a faulttolerant multiprocessor system. 1.
General distributions in process algebra
 IN: LECTURES ON FORMAL METHODS AND PERFORMANCE ANALYSIS: FIRST EEF/EURO SUMMER SCHOOL ON TRENDS IN COMPUTER SCIENCE
, 2001
"... This paper is an informal tutorial on stochastic process algebras, i.e., process calculi where action occurrences may be subject to a delay that is governed by a (mostly continuous) random variable. Whereas most stochastic process algebras consider delays determined by negative exponential distr ..."
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Cited by 11 (1 self)
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This paper is an informal tutorial on stochastic process algebras, i.e., process calculi where action occurrences may be subject to a delay that is governed by a (mostly continuous) random variable. Whereas most stochastic process algebras consider delays determined by negative exponential distributions, this tutorial is concerned with the integration of general, nonexponential distributions into a process algebraic setting. We discuss the issue of incorporating such distributions in an interleaving semantics, and present some existing solutions to this problem. In particular, we present a process algebra for the specification of stochastic discreteevent systems modeled as generalized semiMarkov chains (GSMCs). Using this language stochastic discreteevent systems can be described in an abstract and modular way. The operational semantics of this process algebra is given in terms of stochastic automata, a novel mixture of timed automata and GSMCs. We show that GSMCs are a proper subset of stochastic automata, discuss various notions of equivalence, present congruence results, treat equational reasoning, and argue how an expansion law in the process algebra can be obtained. As a case study, we specify the root contention phase within the standardized IEEE 1394 serial bus protocol and study the delay until root contention resolution. An overview of related work on general distributions in process algebra and a discussion of trends and future work complete this tutorial.