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Implementation of a Compositional Performance Analysis Algorithm for Probabilistic I/O Automata
 IN PROCEEDINGS OF 1999 WORKSHOP ON PROCESS ALGEBRA AND PERFORMANCE MODELING (PAPM99). PRENSAS UNIVERSITARIAS DE
, 1999
"... In previous papers, we defined the probabilistic I/O automata model for specification and modeling of probabilistic concurrent systems, and we showed how certain performance measures for such systems could be computed compositionally, one component at a time, without the need for explicit constr ..."
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Cited by 11 (5 self)
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In previous papers, we defined the probabilistic I/O automata model for specification and modeling of probabilistic concurrent systems, and we showed how certain performance measures for such systems could be computed compositionally, one component at a time, without the need for explicit construction of the full global state space. In this paper, we report on our experiences in constructing and testing a computer implemention of these compositional analysis algorithms. Our implementation, which is coded in the functional programming language Standard ML, uses exact rational arithmetic to calculate performance measures, and it is also capable of producing symbolic rational function expressions that describe the dependence of performance measures on a system parameter.
A Construction and Analysis Tool Based on the Stochastic Process Algebra TIPP
 In Proceedings, TACAS Workshop, volume 1055 of Lecture Notes in Computer Science
, 1996
"... 1 There are many ways to incorporate a notion of time into process algebras in order to integrate functional design and performance analysis. One major research strand, stochastic process algebras, concentrates on the annotation of actions with exponentially distributed random variables. This paper ..."
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Cited by 10 (1 self)
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1 There are many ways to incorporate a notion of time into process algebras in order to integrate functional design and performance analysis. One major research strand, stochastic process algebras, concentrates on the annotation of actions with exponentially distributed random variables. This paper presents a tool for the functional analysis and performance evaluation of complex systems based on the stochastic process algebra paradigm. The TIPPtool provides facilities for model specification, reachability analysis, as well as several numerical algorithms for the solution of the underlying Markov chain and the computation of performance measures. 1 Introduction Stochastic process algebras (SPA) have been introduced as an extension of classical process algebras, like CCS or CSP, with timing information aiming mainly at the integration of functional design and quantitative analysis of computer systems. Time is represented by attaching random variables to every activity in the model, de...
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 10 (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).
Towards a superset of Basic Lotos for Performance Prediction
 Proc. of 6th Process Algebra and Performance Modelling Workshop
, 1996
"... Stochastic process algebras (SPA) provide primitive operators that serve as means to incorporate stochastic timing aspects into a process algebraic specification. In this paper we add some comfortable operators to an SPA where the passing of time is separated from the occurrence of activities. We pr ..."
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Cited by 8 (3 self)
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Stochastic process algebras (SPA) provide primitive operators that serve as means to incorporate stochastic timing aspects into a process algebraic specification. In this paper we add some comfortable operators to an SPA where the passing of time is separated from the occurrence of activities. We present a superset of Basic Lotos which integrates probabilistic branching and exponentially distributed time delays into the language, as well as value passing. The treatment of these ingredients is formally defined on the (interleaving) semantic model. After explaining the details of the language`s semantics, we define a congruence relation based on Milner`s observational congruence that is central for the reduction of the semantic model into a Continuous Time Markov Chain. 1 Introduction Stochastic Process Algebras have emerged from the desire to allow performance analysis of specifications based on process algebras. For this purpose, randomly distributed time delays are associated with ea...
Technique and tool for symbolic representation and manipulation of stochastic transition systems
 TR IMMD 7 2/98, Universitat ErlangenNurnberg
, 1998
"... We present a new approach to the compact symbolic representation of stochastic transition systems, based on Decision Node BDDs, a novel stochastic extension of BDDs. Parallel composition of components can be performed on the basis of this new data structure. We also discuss symbolic state space redu ..."
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Cited by 5 (4 self)
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We present a new approach to the compact symbolic representation of stochastic transition systems, based on Decision Node BDDs, a novel stochastic extension of BDDs. Parallel composition of components can be performed on the basis of this new data structure. We also discuss symbolic state space reduction by Markovian bisimulation. In many areas of system design and analysis, there is the problem of generating, manipulating and analysing very large state spaces. We focus on stochastic labelled transition systems (SLTS) where each transition is labelled by an action name and an exponential delay. Such SLTSs (which originate, e.g., from Stochastic Process Algebra specifications [3]) can be interpreted as Markov chains and used for performability analysis. We propose a novel approach to SLTS representation and manipulation which is based on symbolic techniques. This is motivated by the fact that, in recent years, the problem of representing and analysing large state spaces has been very successfully approached by using Binary Decision Diagrams (BDD) [1]. This work took place in the context of formal verification and model checking, i.e. dealing exclusively with functional behaviour, disregarding temporal aspects. The success of symbolic techniques for functional analysis induced us to experiment with BDDbased representations of stochastic LTS. We introduce a novel data structure, Decision Node BDDs (DNBDD), which can capture not only functional, but also temporal (stochastic) information [4]. The idea is to employ binary encodings of states and transitions and store them in a canonical, graphbased format, a BDD. The information about transition rates is attached to a subset of the BDD nodes (the decision nodes) without modifying the basic structure of the BDD. Complex systems can be most conveniently specified as a number of interacting components. Using traditional representations, parallel composition of components leads to an exponential growth of the state space, since all possible in
Stochastic Process Algebras  Between LOTOS and Markov Chains
 Comp. Netw. and ISDN Syst
, 1997
"... This paper introduces stochastic process algebras as an approach for the structured design and analysis of both the functional behavior and performance characteristics of parallel and distributed systems. This is achieved by integrating stochastic modelling and analysis into process algebras like CC ..."
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Cited by 5 (2 self)
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This paper introduces stochastic process algebras as an approach for the structured design and analysis of both the functional behavior and performance characteristics of parallel and distributed systems. This is achieved by integrating stochastic modelling and analysis into process algebras like CCS or LOTOS. We demonstrate how notions of equivalent behavior  substantial for process algebras  stand in a new light for stochastic process algebras. In particular we discuss the impact of stochastic versions of such equivalences on compositional performance analysis by means of a running example. In addition we discuss analysis techniques, tool support and include a survey of related work as well as recent trends in this area. Keywords: Process Algebra, Performance Analysis, Stochastic Time, Markov Chains, Bisimulation. 1 Introduction  Distributed Systems and their Formal Description One may safely assume that almost all substantial future computer and information systems will be ...
Stochastic Process Algebras  Constructive Specification Techniques Integrating Functional, Performance and Dependability Aspects
 Quantitative Methods in Parallel Systems
, 1995
"... Q uantitative M odeling I n P arallel S ystems ..."
A Compact File Format for Labeled Transition Systems
, 2001
"... A compact open file format for labeled transition systems, which are commonly used in specification and verification of concurrent systems, is introduced. This combination of openness, both in specification and implementation, and compactness is unprecedented, since existing formats in this field ..."
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Cited by 4 (1 self)
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A compact open file format for labeled transition systems, which are commonly used in specification and verification of concurrent systems, is introduced. This combination of openness, both in specification and implementation, and compactness is unprecedented, since existing formats in this field are either not compact, yielding files too large to be easily handled, or proprietary, hampering the development of e#cient tools.
An Operator for Symmetry Representation and Exploitation in Stochastic Process Algebras
 Twente (The Netherlands
, 1997
"... Stochastic process algebras have been introduced to enable compositional performance analysis. State space explosion is a frequently observed problem, especially if the system consists of many cooperating components. This paper introduces symmetric parallel composition, an operator to specify a set ..."
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Cited by 4 (0 self)
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Stochastic process algebras have been introduced to enable compositional performance analysis. State space explosion is a frequently observed problem, especially if the system consists of many cooperating components. This paper introduces symmetric parallel composition, an operator to specify a set of identical components that are cooperating in parallel. Its operational semantics is consistent with usual parallel composition whereas the state space explosion problem is drastically reduced. We highlight this fact by means of a comparative case study. 1 Introduction Compositional application of stochastic process algebra (SPA) is particularly successful, if the system under consideration is given by a large number of identical components. In this case, equivalences (congruences) can be used to exploit symmetries in order to reduce the state space underlying the model. First, however, the symmetries have to be detected by either applying the semantic rules or by introducing some kind of...
Stochastic Process Algebras
"... Abstract. In this tutorial we give an introduction to stochastic process algebras and their use in performance modelling, with a focus on the PEPA formalism. A brief introduction is given to the motivations for extending classical process algebra with stochastic times and probabilistic choice. We th ..."
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Cited by 3 (0 self)
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Abstract. In this tutorial we give an introduction to stochastic process algebras and their use in performance modelling, with a focus on the PEPA formalism. A brief introduction is given to the motivations for extending classical process algebra with stochastic times and probabilistic choice. We then present an introduction to the modelling capabilities of the formalism and the tools available to support Markovian based analysis. The chapter is illustrated throughout by small examples, demonstrating the use of the formalism and the tools. 1