Results 1  10
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11
On Generative Parallel Composition
, 1999
"... A major reason for studying probabilistic processes is to establish a link between a formal model for describing functional system behaviour and a stochastic process. Compositionality is an essential ingredient for specifying systems. Parallel composition in a probabilistic setting is complicated si ..."
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Cited by 36 (6 self)
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A major reason for studying probabilistic processes is to establish a link between a formal model for describing functional system behaviour and a stochastic process. Compositionality is an essential ingredient for specifying systems. Parallel composition in a probabilistic setting is complicated since it gives rise to nondeterminism, for instance due to interleaving of independent autonomous activities. This paper presents a detailed study of the resolution of nondeterminism in an asynchronous generative setting. Based on the intuition behind the synchronous probabilistic calculus PCCS we formulate two criteria that an asynchronous parallel composition should fulfill. We provide novel probabilistic variants of parallel composition for CCS and CSP and show that these operators satisfy these general criteria, opposed to most existing proposals. Probabilistic bisimulation is shown to be a congruence for these operators and their expansion is addressed.
NMSPA: A NonMarkovian Model for Stochastic Processes
, 2000
"... In this paper we introduce a new Stochastic Process Algebra: NMSPA. This new language presents the usual features of stochastic models but probability distributions are not restricted to be exponential. This fact increases the expressive power of the language in several ways. For example, we can sp ..."
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Cited by 8 (0 self)
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In this paper we introduce a new Stochastic Process Algebra: NMSPA. This new language presents the usual features of stochastic models but probability distributions are not restricted to be exponential. This fact increases the expressive power of the language in several ways. For example, we can specify actions that can be executed with probability 1 in a finite amount of time, socalled passive actions fall in a natural way inside our framework, urgency of internal actions can be expressed, etc. In order to define an interleaving semantics for the parallel operator, we benefit from ideas used in timed process algebras. Our operational transitions include information about the time when actions can be executed, as well as the random variable associated with them. We provide our language with a notion of strong bisimulation which takes into account urgency of internal transitions. Finally, we specify the Alternating Bit Protocol. This is a very simple communication protocol where th...
A Probabilistic RealTime Calculus for Performance Evaluation
, 1999
"... In this paper we develop a probabilistic realtime calculus for performance evaluation. The calculus applies a simple generative model of probabilities. Next to probabilistic action transitions, probabilistic time transitions are supported. An operational characterization is given in terms of a labe ..."
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Cited by 7 (7 self)
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In this paper we develop a probabilistic realtime calculus for performance evaluation. The calculus applies a simple generative model of probabilities. Next to probabilistic action transitions, probabilistic time transitions are supported. An operational characterization is given in terms of a labelled transition system. The operational rules for the realtime part of the calculus are constructed in such a way, that the transition system can be interpreted as a discretetime Markov chain. They further yield a constructive approach towards the efficient execution of processes and generation of transition graphs. On top of the operational rules, bisimulation equivalence is defined and proven to be a congruence for all operators. We define three different performance characteristics in terms of reward functions and prove that equivalent processes have an identical performance. Using an ergodic theorem of Markov chains, we further show how these performance figures can be computed in practice. We introduce an experimental software tool and we show how it can be applied to calculate the performance of a nontrivial realtime data communication protocol. 1
Global Timed Bisimulation: An Introduction
, 1999
"... Bisimulations are a broadly used formalism to define the semantics of process algebras. In particular, by means of weak bisimulation most of the internal activity of processes may be abstracted. Unfortunately, this is not fully accomplished: for instance, the internal choice operator becomes nonass ..."
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Cited by 6 (2 self)
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Bisimulations are a broadly used formalism to define the semantics of process algebras. In particular, by means of weak bisimulation most of the internal activity of processes may be abstracted. Unfortunately, this is not fully accomplished: for instance, the internal choice operator becomes nonassociative since bisimulation can see the branching structure of processes. In this paper we propose global timed bisimulation as a weakening of weak timed bisimulation. Global timed bisimulation is defined exactly as weak timed bisimulation once ordinary transitions are replaced by the adequate notions of generalized transitions. In order to asses the definition of our global timed bisimulation we present a collection of small examples that illustrate each of the clauses of that definition. Finally, a more elaborated example is presented to summarize the main properties of that notion.
An Analytical Approach towards System Level Performance Analysis
, 1999
"... System level modeling languages support the creation of executable system models in the earliest stages of the design process. Executable specifications allow the properties of a system to be analyzed and verified before this system is actually being realized in terms of hardware and software compon ..."
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Cited by 3 (3 self)
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System level modeling languages support the creation of executable system models in the earliest stages of the design process. Executable specifications allow the properties of a system to be analyzed and verified before this system is actually being realized in terms of hardware and software components. The POOSL language is a system level modelling language for complex realtime hardware/software systems. The language has proven to be very useful to describe reallife systems and to verify their correctness properties. Unfortunately, currently POOSL does not support the possibility to analyze performance properties. This is a major disadvantage because performance characteristics play a key role in the design of many hardware /software systems. This paper aims at extending the POOSL language with the capabilities to express probabilistic behaviour and to analyze performance figures analytically. The paper complements the work presented in [16] where the focus was on empirical performance analysis. To present the key ideas we develop a realtime probabilistic process calculus that is able to express the basic concepts of POOSL. We introduce an experimental software tool supporting the calculus and it is shown how the tool enables the calculation of the performance of a data link protocol. Keywords systemlevel modeling; performance evaluation; formal specification I.
Partial Order Models for Quantitative Extensions of LOTOS
, 1997
"... Event structures are a prominent model for noninterleaving concurrency. The use of event structures for providing a compositional noninterleaving semantics to LOTOS without data is studied. In particular, several quantitative extensions of event structures are proposed that incorporate notions lik ..."
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Cited by 3 (1 self)
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Event structures are a prominent model for noninterleaving concurrency. The use of event structures for providing a compositional noninterleaving semantics to LOTOS without data is studied. In particular, several quantitative extensions of event structures are proposed that incorporate notions like timeboth of deterministic and stochastic natureand probability. The suitability of these models for giving a noninterleaving semantics to a timed, stochastic and probabilistic extension of LOTOS is investigated. Consistency between the event structure semantics and an (eventbased) operational semantics is addressed for the different quantitative variants of LOTOS and is worked out for the timed case in more detail. These consistency results facilitate the coherent use of an interleaving and a noninterleaving semantic view in a single design trajectory and provide a justification for the event structure semantics. As a running example an infinite buffer is used in which gradually t...
An Axiomatization of Probabilistic Testing
, 1999
"... In this paper we present a sound and complete axiom system for a probabilistic process algebra with recursion. Soundness and completeness of the axiomatization is given with respect to the testing semantics defined in [19]. ..."
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Cited by 2 (1 self)
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In this paper we present a sound and complete axiom system for a probabilistic process algebra with recursion. Soundness and completeness of the axiomatization is given with respect to the testing semantics defined in [19].
Fair Testing Through Probabilistic Testing
, 1999
"... In this paper we define a probabilistic testing semantics which can be used to alternatively characterize fair testing. The key idea is to define a probabilistic semantics in such a way that two nonprobabilistic processes are fair equivalent iff any probabilistic version of both processes are equiv ..."
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Cited by 2 (1 self)
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In this paper we define a probabilistic testing semantics which can be used to alternatively characterize fair testing. The key idea is to define a probabilistic semantics in such a way that two nonprobabilistic processes are fair equivalent iff any probabilistic version of both processes are equivalent in our probabilistic testing semantics. In order to get this result we define a simple probabilistic must semantics by saying that a probabilistic process must pass a test iff the probability with which the process passes the test equals 1. Finally, we present an algorithm for deciding whether the probability with which a finitestate process passes a finitestate test equals 1. Alternatively, this algorithm can be used for computing whether a finitestate process fairly passes a finitestate test. Keywords: Testing semantics, fair testing, probabilistic processes. 1. INTRODUCTION Formal models of concurrency have been proved to be very useful to properly specify concurrent and distr...
Denotational Semantics for Probabilistic Refusal Testing
, 1999
"... In this paper, refusal testing ideas are applied to define a testing semantics for a probabilistic process algebra. A testing equivalence is defined by combining the greater discriminatory power of refusal testing and a simple treatment of the probabilistic component of processes. This testing equiv ..."
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Cited by 1 (0 self)
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In this paper, refusal testing ideas are applied to define a testing semantics for a probabilistic process algebra. A testing equivalence is defined by combining the greater discriminatory power of refusal testing and a simple treatment of the probabilistic component of processes. This testing equivalence is characterized by two fully abstract denotational semantics. The first of them is based on probabilistic refusal traces. These traces condense the set of tests that a process passes with probability greater than zero. The second one is based on a probabilistic extension of classical acceptance trees, where semantic processes can be viewed as (syntactic) normal forms.
Specifying and Verifying the Alternating Bit Protocol with ProbabilisticTimed LOTOS
, 1996
"... In this paper we use a probabilistictimed version of Lotos (PTLotos) for specifying and verifying the Alternating Bit Protocol (ABP). First, we present the language which is an upward compatible version of Lotos where some new operators to deal with time and probabilistic features have been include ..."
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In this paper we use a probabilistictimed version of Lotos (PTLotos) for specifying and verifying the Alternating Bit Protocol (ABP). First, we present the language which is an upward compatible version of Lotos where some new operators to deal with time and probabilistic features have been included. We give an operational semantics, where there are two kinds of transitions: probabilistic transitions and timed transitions. Transitions of the first kind are associated with the events that a behavior expression can execute, while timed transitions deal with time evolution. From this operational semantics we define a testing semantics, where a process passes a test with a probability in a period of time, and two processes are intended to be equivalent if they pass all the tests with the same probability for any time. In the second part of the paper, we use PTLotos in order to specify the Alternating Bit Protocol. The ABP is a simple communication protocol which provides an error free co...