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72
MoDeST: A compositional modeling formalism for hard and softly timed systems
, 2005
"... This paper presents Modest (MOdeling and DEscription language for Stochastic Timed systems), a formalism that is aimed to support (i) the modular description of reactive system’s behaviour while covering both (ii) functional and (iii) nonfunctional system aspects such as timing and qualityofservi ..."
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This paper presents Modest (MOdeling and DEscription language for Stochastic Timed systems), a formalism that is aimed to support (i) the modular description of reactive system’s behaviour while covering both (ii) functional and (iii) nonfunctional system aspects such as timing and qualityofservice constraints in a single specification. The language contains features such as simple and structured data types, structuring mechanisms like parallel composition and abstraction, means to control the granularity of assignments, exception handling, and nondeterministic and random branching and timing. Modest can be viewed as an overarching notation for a wide spectrum of models, ranging from labeled transition systems, to timed automata (and probabilistic variants thereof) as well as prominent stochastic processes such as (generalized semi)Markov chains and decision processes. The paper describes the design rationales and details of the syntax and semantics. Key words: modeling formalism, compositionality, formal semantics, timed automata, stochastic processes
Automated performance and dependability evaluation using model checking
 In Performance Evaluation of Complex Systems: Techniques and Tools, Performance 2002, Tutorial Lectures
, 2002
"... Abstract. Markov chains (and their extensions with rewards) have been widely used to determine performance, dependability and performability characteristics of computer communication systems, such as throughput, delay, mean time to failure, or the probability to accumulate at least a certain amount ..."
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Abstract. Markov chains (and their extensions with rewards) have been widely used to determine performance, dependability and performability characteristics of computer communication systems, such as throughput, delay, mean time to failure, or the probability to accumulate at least a certain amount of reward in a given time. Due to the rapidly increasing size and complexity of systems, Markov chains and Markov reward models are difficult and cumbersome to specify by hand at the statespace level. Therefore, various specification formalisms, such as stochastic Petri nets and stochastic process algebras, have been developed to facilitate the specification of these models at a higher level of abstraction. Uptill now, however, the specification of the measureofinterest is often done in an informal and relatively unstructured way. Furthermore, some measuresofinterest can not be expressed conveniently at all. In this tutorial paper, we present a logicbased specification technique to specify performance, dependability and performability measuresofinterest and show how for a given finite Markov chain (or Markov reward model) such measures can be evaluated in a fully automated way. Particular emphasis will be given to socalled pathbased measures and hierarchicallyspecified measures. For this purpose, we extend socalled model checking techniques to reason about discrete and continuoustime Markov chains and their rewards. We also report on the use of techniques such as (compositional) model reduction and measuredriven statespace generation to combat the infamous state space explosion problem. 1
A processalgebraic language for probabilistic I/O automata
 IN PROC. OF THE 14TH INT. CONF. ON CONCURRENCY THEORY (CONCUR 2003), LNCS
, 2003
"... We present a processalgebraic language for Probabilistic I/O Automata (PIOA). To ensure that PIOA specifications given in our language satisfy the “inputenabled” property, which requires that all input actions be enabled in every state of a PIOA, we augment the language with a set of type inferenc ..."
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Cited by 16 (2 self)
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We present a processalgebraic language for Probabilistic I/O Automata (PIOA). To ensure that PIOA specifications given in our language satisfy the “inputenabled” property, which requires that all input actions be enabled in every state of a PIOA, we augment the language with a set of type inference rules. We also equip our language with a formal operational semantics defined by a set of transition rules. We present a number of results whose thrust is to establish that the typing and transition rules are sensible and interact properly. The central connection between types and transition systems is that if a term is welltyped, then in fact the associated transition system is inputenabled. We also consider two notions of equivalence for our language, weighted bisimulation equivalence and PIOA behavioral equivalence. We show that both equivalences are substitutive with respect to the operators of the language, and note that weighted bisimulation equivalence is a strict refinement of behavioral equivalence.
Branching cells as local states for event structures and nets: Probabilistic applications
 In Proceedings of 8th FoSSaCS, volume 3441 of LNCS
, 2005
"... Abstract. We study the concept of choice for true concurrency models such as prime event structures and safe Petri nets. We propose a dynamic variation of the notion of cluster previously introduced for nets. This new object is defined for event structures, it is called a branching cell. Our aim is ..."
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Cited by 15 (9 self)
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Abstract. We study the concept of choice for true concurrency models such as prime event structures and safe Petri nets. We propose a dynamic variation of the notion of cluster previously introduced for nets. This new object is defined for event structures, it is called a branching cell. Our aim is to bring an interpretation of branching cells as a right notion of “local state”, for concurrent systems. We illustrate the above claim through applications to probabilistic concurrent models. In this respect, our results extends in part previous work by VaraccaVölzerWinskel on probabilistic confusion free event structures. We propose a construction for probabilities over socalled locally finite event structures that makes concurrent processes probabilistically independent—simply attach a dice to each branching cell; dices attached to concurrent branching cells are thrown independently. Furthermore, we provide a true concurrency generalization of Markov chains, called Markov nets. Unlike in existing variants of stochastic Petri nets, our approach randomizes Mazurkiewicz traces, not firing sequences. We show in this context the Law of Large Numbers (LLN), which confirms that branching cells deserve the status of local state. Our study was motivated by the stochastic modeling of fault propagation and alarm correlation in telecommunications networks and services. It provides the foundations for probabilistic diagnosis, as well as the statistical distributed learning of such models. 1
Structural Operational Semantics for Stochastic Process Calculi
"... Abstract. A syntactic framework called SGSOS, for defining wellbehaved Markovian stochastic transition systems, is introduced by analogy to the GSOS congruence format for nondeterministic processes. Stochastic bisimilarity is guaranteed a congruence for systems defined by SGSOS rules. Associativity ..."
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Abstract. A syntactic framework called SGSOS, for defining wellbehaved Markovian stochastic transition systems, is introduced by analogy to the GSOS congruence format for nondeterministic processes. Stochastic bisimilarity is guaranteed a congruence for systems defined by SGSOS rules. Associativity of parallel composition in stochastic process algebras is also studied within the framework. 1
Concurrency and Composition in a Stochastic World
, 2012
"... Abstract. We discuss conceptional and foundational aspects of Markov automata [22]. We place this model in the context of continuous and discretetime Markov chains, probabilistic automata and interactive Markov chains, and provide insight into the parallel execution of such models. We further give ..."
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Cited by 12 (3 self)
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Abstract. We discuss conceptional and foundational aspects of Markov automata [22]. We place this model in the context of continuous and discretetime Markov chains, probabilistic automata and interactive Markov chains, and provide insight into the parallel execution of such models. We further give a detailled account of the concept of relations on distributions, and discuss how this can generalise known notions of weak simulation and bisimulation, such as to fuse sequences of internal transitions. 1
Quantitative analysis of enterprise architectures
, 2004
"... Abstract. Enterprise architecture is concerned with a description of all the relevant elements that make up an enterprise and how these elements interrelate. It covers aspects ranging from the technical infrastructure, through software applications, to business processes and products. The relations ..."
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Cited by 10 (1 self)
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Abstract. Enterprise architecture is concerned with a description of all the relevant elements that make up an enterprise and how these elements interrelate. It covers aspects ranging from the technical infrastructure, through software applications, to business processes and products. The relations between these layers play a central role. Also from a quantitative analysis perspective, the layers are interrelated: the higher layers impose a workload on the lower layers, while the performance characteristics of the lower layers directly influence the performance of the higher layers. This paper presents an approach for quantitative analysis of layered, servicebased enterprise architecture models, which consists of two phases: a ‘topdown ’ propagation of workload parameters, and a ‘bottomup ’ propagation of performance or cost measures. By means of an example we demonstrate the application of the approach, and show that a seamless integration with other performance analysis methods (e.g., queueing analysis) can be achieved. 1
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 10 (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...
Software Performance Modeling using UML and Petri Nets
"... Software systems are today one of the most complex artifacts, they are simultaneously used by hundredthousand of people sometimes in risk real time operations, such as auctions or electronic commerce. ..."
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Cited by 9 (0 self)
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Software systems are today one of the most complex artifacts, they are simultaneously used by hundredthousand of people sometimes in risk real time operations, such as auctions or electronic commerce.
Advances in Model Representations
 Proc. PAPM/PROBMIV 2001, Available as Volume 2165 of LNCS (2001
, 2001
"... We review highlevel specification formalisms for Markovian performability models, thereby emphasising the role of structuring concepts as realised par excellence by stochastic process algebras. Symbolic representations based on decision diagrams are presented, and it is shown that they quite id ..."
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Cited by 9 (4 self)
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We review highlevel specification formalisms for Markovian performability models, thereby emphasising the role of structuring concepts as realised par excellence by stochastic process algebras. Symbolic representations based on decision diagrams are presented, and it is shown that they quite ideally support compositional model construction and analysis.