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Basic Observables for Processes
 Information and Computation
, 1999
"... A general approach for defining behavioural preorders over process terms as the maximal precongruences induced by basic observables is examined. Three different observables, that provide information about the initial communication capabilities of processes and about the possibility that processes ..."
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A general approach for defining behavioural preorders over process terms as the maximal precongruences induced by basic observables is examined. Three different observables, that provide information about the initial communication capabilities of processes and about the possibility that processes get engaged in divergent computations, will be considered. We show that the precongruences induced by our basic observables coincide with intuitive and/or widely studied behavioural preorders. In particular, we retrieve in our setting the must preorder of De Nicola and Hennessy and the fair/should preorder introduced by Cleaveland and Natarajan and by Brinksma, Rensink and Vogler. A new form of testing preorder, which we call safemust, also emerges. The alternative characterizations we offer shed light on the differences between these preorders, and on the role played in their definition by tests for divergence. 1 Introduction In the classical theory of functional programming, the point...
Bisimulation on speed: A unified approach
 Theoretical Computer Science
, 2005
"... Abstract. Two process–algebraic approaches have been developed for comparing two bisimulation–equivalent processes with respect to speed: the one of Moller/Tofts equips actions with lower time bounds, while the one by Lüttgen/Vogler considers upper time bounds instead. This paper sheds new light on ..."
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Abstract. Two process–algebraic approaches have been developed for comparing two bisimulation–equivalent processes with respect to speed: the one of Moller/Tofts equips actions with lower time bounds, while the one by Lüttgen/Vogler considers upper time bounds instead. This paper sheds new light on both approaches by testifying to their close relationship. We introduce a general, intuitive concept of “faster– than”, which is formalised by a notion of amortised faster–than preorder. When closing this preorder under all contexts, exactly the two faster– than preorders investigated by Moller/Tofts and Lüttgen/Vogler arise. For processes incorporating both lower and upper time bounds we also show that the largest precongruence contained in the amortised faster– than preorder is not a proper preorder but a timed bisimulation. In the light of this result we systematically investigate under which circumstances the amortised faster–than preorder degrades to an equivalence. 1
Comparing the WorstCase Efficiency of Asynchronous Systems with PAFAS
"... A timed CCSlike process algebra PAFAS and a testing scenario are developed for evaluating the temporal worstcase efficiency of asynchronous concurrent systems. Each action is associated with a maximal time delay, which allows components to work with arbitrary relative speeds; for simplicity, the ..."
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Cited by 9 (8 self)
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A timed CCSlike process algebra PAFAS and a testing scenario are developed for evaluating the temporal worstcase efficiency of asynchronous concurrent systems. Each action is associated with a maximal time delay, which allows components to work with arbitrary relative speeds; for simplicity, the maximal delay is 1 or 0, but time is continuous. The canonical testing preorder associated to our timed testing compares worstcase efficiency; we show that this efficiency preorder can equivalently be defined considering only discrete time, which is of course much simpler. Then we characterize the efficiency preorder with some kind of refusal traces; despite the rather weak control an asynchronous test environment has, this gives quite detailed insight into the temporal system behaviour. Since the preorder is not a precongruence for choice, we refine it to the efficiency precongruence, which is a precongruence for all operators of the algebra including recursion.
Comparing the Efficiency of Asynchronous Systems
 IN PROC. OF AMAST WORKSHOP ON REALTIME AND PROBABILISTIC SYSTEMS, LNCS
, 1999
"... A timed process algebra is developed for evaluating the temporal worstcase efficiency of asynchronous concurrent systems. For the sake of simplicity, we use a classical CCSlike algebra where actions may occur arbitrarily within a continuous time interval, yielding arbitrary relative speeds of the ..."
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Cited by 5 (4 self)
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A timed process algebra is developed for evaluating the temporal worstcase efficiency of asynchronous concurrent systems. For the sake of simplicity, we use a classical CCSlike algebra where actions may occur arbitrarily within a continuous time interval, yielding arbitrary relative speeds of the components. Via the timed testing approach, asynchronous systems are then related w.r.t. their worstcase efficiency, yielding an efficiency preorder. We show that this preorder can just as well be based on much simpler discrete time and that it can be characterized with some kind of refusal traces. Finally, precongruence results are provided for all operators of the algebra, where prefix, choice and recursion require special attention.
Efficiency of asynchronous systems, read arcs, and the MUTEXproblem
 TCS
, 1997
"... Two solutions to the MUTEXproblem are compared w.r.t. their temporal efficiency. For this, a formerly developed efficiency testing for asynchronous systems is adapted to Petri nets with socalled read arcs. Furthermore, a compositional semantics for fair behaviour (in the sense of the progress assu ..."
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Two solutions to the MUTEXproblem are compared w.r.t. their temporal efficiency. For this, a formerly developed efficiency testing for asynchronous systems is adapted to Petri nets with socalled read arcs. Furthermore, a compositional semantics for fair behaviour (in the sense of the progress assumption) is presented. On the one hand, this semantics is related to efficiency testing; on the other hand, it is used to specify formally what a solution to the MUTEXproblem is. It is shown that one of our solutions indeed satisfies this specification and that ordinary nets without read arcs cannot solve the MUTEXproblem.
Bisimulation on speed: Lower time bounds
 RAIRO Theoretical Informatics and Applications
, 2004
"... More than a decade ago, Moller and Tofts published their seminal work on relating processes that are annotated with lower time bounds, with respect to speed. Their paper has left open many questions concerning the semantic theory for their suggested bisimulationbased fasterthan preorder, the MT ..."
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More than a decade ago, Moller and Tofts published their seminal work on relating processes that are annotated with lower time bounds, with respect to speed. Their paper has left open many questions concerning the semantic theory for their suggested bisimulationbased fasterthan preorder, the MTpreorder, which have not been addressed since. The encountered difficulties concern a general compositionality result, a complete axiom system for finite processes, and a convincing intuitive justification of the MTpreorder. This paper solves these difficulties by developing and employing novel tools for reasoning in discretetime process algebra, in particular a general commutation lemma relating the sequencing of action and clock transitions. Most importantly, it is proved that the MT–preorder is fullyabstract with respect to a natural amortized preorder that uses a simple bookkeeping mechanism for deciding whether one process is faster than another. Together these results reveal the intuitive roots of the MTpreorder as a faster–than relation, while testifying to its semantic elegance. This lifts some of the barriers that have so far hampered progress in semantic theories for comparing the speed of processes.
Testing processes for efficiency
 FSTTCS 16, Hyderabad 1996, Lecture Notes in Computer Science
, 1996
"... Two notions for comparing the efficiencies of equivalent concurrent systems have been developed and axiomatized in [1] and [2]. Recently Natarajan and Cleaveland have defined a notion of testing [6] which incorporates these ideas as an extension of the testing methodology ([3], [4]). Their extensi ..."
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Two notions for comparing the efficiencies of equivalent concurrent systems have been developed and axiomatized in [1] and [2]. Recently Natarajan and Cleaveland have defined a notion of testing [6] which incorporates these ideas as an extension of the testing methodology ([3], [4]). Their extension bounds the run of a test in an effort to compare processes for their relative efficiencies, measured in terms of the amount of internal activity in a process. In this paper we explore the feasibility of obtaining other efficiency based preorders in the setting of the testing methodology. We generalize the testing methodology and cast [3] and [6] in the new framework. Further, we provide a variation that is equivalent to that of [6]. Another alternative that we explore is what we call "testing for efficiency". Rather than bound the test runs externally, testing for internal activity in a process is woven into the test itself. This turns out to be a more powerful and
flexible method of testing processes for a variety of properties. The main result of this paper is that the testingefficiency preorders obtained from all the variations previously considered are coarser than that obtained by "testing for efficiency". We prove appropriate alternate characterizations that are independent of any testing formalism. We also show that the existing methodologies (including [3]) or their equivalent variations can be simulated in the "testing for efficiency" framework.
An Algebraic Framework for Optimizing Parallel Programs
 Proceedings of Symposium on Software Engineering for Parallel and Distributed Systems, pp.28–38, IEEE
, 1998
"... This paper proposes a theoretical framework for verifying and deriving code optimizations for programs written in parallel programming languages. The key idea of this framework is to formalize code optimizations as compositional transformation rules for programs presented as terms of an enriched pro ..."
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This paper proposes a theoretical framework for verifying and deriving code optimizations for programs written in parallel programming languages. The key idea of this framework is to formalize code optimizations as compositional transformation rules for programs presented as terms of an enriched process calculus. The rules are formulated on the basis of an algebraic order relation between two programs which states that they are behaviorally equivalent and one of them is faster than the other. The correctness and e#ectiveness of optimized programs derived from the rules can be ensured in all circumstances. The framework is unique among other existing works in being able to quantitatively analyze the temporal costs of synchronizations among parallel programs. This paper presents basic ideas and definitions of the framework with several examples. 1. Introduction Parallel computation will play an increasingly important role in many areas of computer systems. As it becomes popular, custome...
A Theory of Efficiency for Markovian Processes
, 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 9811 Structuring SubPopulations in Parallel Genetic Algorithms for MPP, R. Gaioni, R. Dav ..."
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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 9811 Structuring SubPopulations in Parallel Genetic Algorithms for MPP, R. Gaioni, R. Davoli, June 1998. 9812 The Jgroup Reliable Distributed Object Model, A. Montresor, December 1998 (Revised March 1999). 991 Deciding and Axiomatizing ST Bisimulation for a Process Algebra with Recursion and Action Refinement, M. Bravetti, R. Gorrieri, February 1999. 992 A Theory of Efficiency for Markovian Processes, M. Bernardo, W.R. Cleaveland, February 1999. 993 A Reliable Registry for the Jgroup Distributed Object Model, A. Montresor, March 1999. 994 Comparing the QoS of Internet Audio Mechanisms via Formal Methods, A. Aldini, M. Bernardo, R. Gorrieri, M. Roccetti, March 1999. 995 GroupEnhanced Remote Method Invocations, A. Montresor, R. Davoli, O. Babao glu, April 1999. 996 Managi...