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Priorities in process algebra
, 1999
"... This chapter surveys the semantic rami cations of extending traditional process algebras with notions of priority that allow for some transitions to be given precedence over others. The need for these enriched formalisms arises when one wishes to model system features such asinterrupts, prioritized ..."
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Cited by 120 (12 self)
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This chapter surveys the semantic rami cations of extending traditional process algebras with notions of priority that allow for some transitions to be given precedence over others. The need for these enriched formalisms arises when one wishes to model system features such asinterrupts, prioritized choice, orrealtime behavior. Approaches to priority in process algebras can be classi ed according to whether the induced notion of preemption on transitions is global or local and whether priorities are static or dynamic. Early work in the area concentrated on global preemption and static priorities and led to formalisms for modeling interrupts and aspects of realtime, such as maximal progress, in centralized computing environments. More recent research has investigated localized notions of preemption in which the distribution of systems is taken into account, as well as dynamic priority approaches, i.e., those where priority values may change as systems evolve. The latter allows one to model behavioral phenomena such as scheduling algorithms and also enables the e cient encoding of realtime semantics. Technically, this chapter studies the di erent models of priorities by presenting extensions of Milner's Calculus of Communicating Systems (CCS) with static and dynamic priority as well as with notions of global and local preemption. In each case the operational semantics of CCS is modi ed appropriately, behavioral theories based on strong and weak bisimulation are given, and related approaches for di erent processalgebraic settings are discussed.
A tutorial on EMPA: A theory of concurrent processes with nondeterminism, priorities, probabilities and time
 Theoretical Computer Science
, 1998
"... In this tutorial we give an overview of the process algebra EMPA, a calculus devised in order to model and analyze features of realworld concurrent systems such as nondeterminism, priorities, probabilities and time, with a particular emphasis on performance evaluation. The purpose of this tutorial ..."
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Cited by 118 (11 self)
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In this tutorial we give an overview of the process algebra EMPA, a calculus devised in order to model and analyze features of realworld concurrent systems such as nondeterminism, priorities, probabilities and time, with a particular emphasis on performance evaluation. The purpose of this tutorial is to explain the design choices behind the development of EMPA and how the four features above interact, and to show that a reasonable trade off between the expressive power of the calculus and the complexity of its underlying theory has been achieved.
A Calculus of Broadcasting Systems
 SCIENCE OF COMPUTER PROGRAMMING
, 1991
"... CBS is a simple and natural CCSlike calculus where processes speak one at a time and are heard instantaneously by all others. Speech is autonomous, contention between speakers being resolved nondeterministically, but hearing only happens when someone else speaks. Observationally meaningful laws dif ..."
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Cited by 75 (8 self)
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CBS is a simple and natural CCSlike calculus where processes speak one at a time and are heard instantaneously by all others. Speech is autonomous, contention between speakers being resolved nondeterministically, but hearing only happens when someone else speaks. Observationally meaningful laws differ from those of CCS. The change from handshake communication in CCS to broadcast in CBS permits several advances. (1) Priority, which attaches only to autonomous actions, is simply added to CBS in contrast to CCS, where such actions are the result of communication. (2) A CBS simulator runs a process by returning a list of values it broadcasts. This permits a powerful combination, CBS with the host language. It yields several elegant algorithms. Only processes with a unique response to each input are needed in practice, so weak bisimulation is a congruence. (3) CBS subsystems are interfaced by translators; by mapping messages to silence, these can restrict hearing and hide speech. Reversi...
A Process Algebraic Approach to the Specification and Analysis of ResourceBound RealTime Systems
 PROCEEDINGS OF THE IEEE
, 1994
"... Recently, significant progress has been made in the development of timed process algebras for the specification and analysis of realtime systems. This paper describes a timed process algebra called ACSR, which supports synchronous timed actions and asynchronous instantaneous events. Timed actions a ..."
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Cited by 74 (48 self)
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Recently, significant progress has been made in the development of timed process algebras for the specification and analysis of realtime systems. This paper describes a timed process algebra called ACSR, which supports synchronous timed actions and asynchronous instantaneous events. Timed actions are used to represent the usage of resources and to model the passage of time. Events are used to capture synchronization between processes. To be able to specify real systems accurately, ACSR supports a notion of priority that can be used to arbitrate among timed actions competing for the use of resources and among events that are ready for synchronization. The paper also includes a brief overview of other timed process algebras and discusses similarities and differences between them and ACSR.
A ResourceBased Prioritized Bisimulation for RealTime Systems
 Information and Computation
, 1992
"... The behavior of concurrent, realtime systems can be specified using a process algebra called CCSR. The underlying computation model of CCSR is resourcebased, in which multiple resources execute synchronously, while processes assigned to the same resource are interleaved according to their prioriti ..."
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Cited by 21 (6 self)
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The behavior of concurrent, realtime systems can be specified using a process algebra called CCSR. The underlying computation model of CCSR is resourcebased, in which multiple resources execute synchronously, while processes assigned to the same resource are interleaved according to their priorities. CCSR allows the algebraic specification of timeouts, interrupts, periodic behaviors and exceptions. This paper develops a natural treatment of preemption, which is based not only on priority, but also on resource utilization and interresource synchronization. The preemption ordering leads to a term equivalence based on strong bisimulation, which is also a congruence with respect to the operators. Consequently the equivalence yields a compositional proof system, which is illustrated in the verification of a resourcesharing, producerconsumer problem. April 1, 1992 3 1 Introduction The timing behavior of a realtime system depends not only on delays due to process synchronization, bu...
Programming With Broadcasts
 In CONCUR
, 1993
"... . [Pra91, Pra92] develop CBS, a CCSlike calculus [Mil89] where processes communicate by broadcasting values along a single channel. These values are hidden or restricted by translation to noise. This paper types CBS and restricts it to processes with a unique response to each input. Nondeterminism ..."
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Cited by 20 (7 self)
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. [Pra91, Pra92] develop CBS, a CCSlike calculus [Mil89] where processes communicate by broadcasting values along a single channel. These values are hidden or restricted by translation to noise. This paper types CBS and restricts it to processes with a unique response to each input. Nondeterminism arises only if two processes in parallel both wish to transmit. These restrictions do not reduce the programming power of CBS. But strong and weak bisimulation can now be defined exactly as in CCS, yet capture observationally meaningful relations. Weak bisimulation is a congruence. This paper also shows how to program in CBS in a (lazy) ML framework. A simple CBS simulator is given, and a parallel implementation discussed. The simulator represents data evaluation, recursion and conditionals directly in Lazy ML. It implements an extended CBS with evaluation as well as communication transitions. [Pra91, Pra92] develop a CCSlike [Mil89] calculus of broadcasting systems, CBS. This paper continu...
Priority as Extremal Probability
, 1992
"... We extend the stratified model of probabilistic processes presented in [vGSST90] to obtain a very general notion of process priority . The main idea is to allow probability guards of value 0 to be associated with alternatives of a probabilistic summation expression. Such alternatives can be chosen o ..."
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Cited by 18 (2 self)
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We extend the stratified model of probabilistic processes presented in [vGSST90] to obtain a very general notion of process priority . The main idea is to allow probability guards of value 0 to be associated with alternatives of a probabilistic summation expression. Such alternatives can be chosen only if the nonzero alternatives are precluded by contextual constraints. We refer to this model as one of "extremal probability" and to its signature as PCCS i , where the i signifies the possibility of zeroprobability alternatives. We provide PCCS i with a structured operational semantics and a notion of probabilistic bisimulation, which is shown to be a congruence. Of particular interest is the abstraction PCCS ß of PCCS i in which all nonzero probability guards are identified. Both the operational and bisimulation semantics of PCCS i easily adapt to this abstraction. PCCS ß represents a customized framework for reasoning about priority, and covers all features of process algebras pro...
Modeling and verifying distributed systems using priorities: A case study
 Software Concepts and Tools
, 1996
"... ABSTRACT This paper illustrates the use of priorities in process algebras by a realworld example dealing with the design of a safetycritical network that is part of a railway signaling system. Priorities in process algebras support an intuitive modeling of distributed systems since undesired inter ..."
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Cited by 17 (8 self)
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ABSTRACT This paper illustrates the use of priorities in process algebras by a realworld example dealing with the design of a safetycritical network that is part of a railway signaling system. Priorities in process algebras support an intuitive modeling of distributed systems since undesired interleavings can be suppressed. This fact also leads to a substantial reduction of the sizes of models. We have implemented a CCSbased process algebra with priorities as a new frontend for the NCSU Concurrency Workbench, and we used model checking for verifying properties of the signaling system.
Denotational Semantics for ProcessBased Simulation Languages. Part I: piDemos
, 1997
"... In this paper we present a method for translating the synchronisation behaviour of a process oriented discrete event simulation language into a process algebra. Such translations serve two purposes. The first exploits the formal structure of the target process algebraic representations to provide pr ..."
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Cited by 17 (10 self)
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In this paper we present a method for translating the synchronisation behaviour of a process oriented discrete event simulation language into a process algebra. Such translations serve two purposes. The first exploits the formal structure of the target process algebraic representations to provide proofs of properties of the source system (such as deadlock freedom, fairness, liveness, ...) which can be very difficult to establish by simulation experiment. The second exploits the denotational semantics to better understand the language constructs as abstract entities and to reason about simulation models. Here we give the intuition and present the basic mechanisms using the ßDemos simulation language and the CCS and SCCS process algebras. The analysis of the synchronisations of full Demos is treated in a companion paper.
CCS with Priority Guards
"... It has long been recognised that ordinary process algebra has difficulty dealing with actions of different priority, such as for instance an interrupt action of high priority. Various solutions have been proposed. We introduce a new approach, involving the addition of “priority guards” to the summat ..."
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Cited by 16 (3 self)
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It has long been recognised that ordinary process algebra has difficulty dealing with actions of different priority, such as for instance an interrupt action of high priority. Various solutions have been proposed. We introduce a new approach, involving the addition of “priority guards” to the summation operator of Milner’s process calculus CCS. In our approach, priority is unstratified, meaning that actions are not assigned fixed levels, so that the same action can have different priority depending where it appears in a program. An important feature is that, unlike in other unstratified accounts of priority in CCS (such as that of Camilleri and Winskel), we can treat inputs and outputs symmetrically. We introduce the new calculus, give examples, develop its theory (including bisimulation, equational laws and logics), and compare it with existing approaches.