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444
Concurrent Constraint Programming
, 1993
"... This paper presents a new and very rich class of (concurrent) programming languages, based on the notion of comput.ing with parhal information, and the concommitant notions of consistency and entailment. ’ In this framework, computation emerges from the interaction of concurrently executing agent ..."
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Cited by 502 (16 self)
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This paper presents a new and very rich class of (concurrent) programming languages, based on the notion of comput.ing with parhal information, and the concommitant notions of consistency and entailment. ’ In this framework, computation emerges from the interaction of concurrently executing agents that communicate by placing, checking and instantiating constraints on shared variables. Such a view of computation is interesting in the context of programming languages because of the ability to represent and manipulate partial information about the domain of discourse, in the context of concurrency because of the use of constraints for communication and control, and in the context of AI because of the availability of simple yet powerful mechanisms for controlling inference, and the promise that very rich representational/programming languages, sharing the same set of abstract properties, may be possible. To reflect this view of computation, [Sar89] develops the cc family of languages. We present here one member of the family, CC(.L,+) (pronounced “cc with Ask and Choose”) which provides the basic operations of blocking Ask and atomic Tell and an algebra of behaviors closed under prefixing, indeterministic choice, interleaving, and hiding, and provides a mutual recursion operator. cc(.L,t) is (intentionally!) very similar to Milner’s CCS, but for the radically different underlying concept of communication, which, in fact, pro’ The class is founded on the notion of “constraint logic programming ” [JL87,Mah87], fundamentally generalizes concurrent logic programming, and is the subject of the first author’s dissertation [Sar89], on which this paper is substantially based.
ADEPT flex  Supporting Dynamic Changes of Workflows Without Loosing Control
 Journal of Intelligent Information Systems
, 1998
"... . Today's workflow management systems (WFMSs) are only applicable in a secure and safe manner if the business process (BP) to be supported is wellstructured and there is no need for ad hoc deviations at runtime. As only few BPs are static in this sense, this significantly limits the applicabil ..."
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Cited by 424 (112 self)
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. Today's workflow management systems (WFMSs) are only applicable in a secure and safe manner if the business process (BP) to be supported is wellstructured and there is no need for ad hoc deviations at runtime. As only few BPs are static in this sense, this significantly limits the applicability of current workflow (WF) technology. On the other hand, to support dynamic deviations from premodeled task sequences must not mean that the responsibility for the avoidance of consistency problems and runtime errors is now completely shifted to the (naive) end user. In this paper we present a formal foundation for the support of dynamic structural changes of running WF instances. Based upon a formal WF model (ADEPT), we define a complete and minimal set of change operations (ADEPT flex ) that support users in modifying the structure of a running WF, while maintaining its (structural) correctness and consistency. The correctness properties defined by ADEPT are used to determine whether a spec...
Probabilistic Simulations for Probabilistic Processes
, 1994
"... Several probabilistic simulation relations for probabilistic systems are defined and evaluated according to two criteria: compositionality and preservation of "interesting" properties. Here, the interesting properties of a system are identified with those that are expressible in an untimed ..."
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Cited by 367 (22 self)
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Several probabilistic simulation relations for probabilistic systems are defined and evaluated according to two criteria: compositionality and preservation of "interesting" properties. Here, the interesting properties of a system are identified with those that are expressible in an untimed version of the Timed Probabilistic concurrent Computation Tree Logic (TPCTL) of Hansson. The definitions are made, and the evaluations carried out, in terms of a general labeled transition system model for concurrent probabilistic computation. The results cover weak simulations, which abstract from internal computation, as well as strong simulations, which do not.
Relations in Concurrency
"... The theme of this paper is profunctors, and their centrality and ubiquity in understanding concurrent computation. Profunctors (a.k.a. distributors, or bimodules) are a generalisation of relations to categories. Here they are first presented and motivated via spans of event structures, and the seman ..."
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Cited by 304 (36 self)
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The theme of this paper is profunctors, and their centrality and ubiquity in understanding concurrent computation. Profunctors (a.k.a. distributors, or bimodules) are a generalisation of relations to categories. Here they are first presented and motivated via spans of event structures, and the semantics of nondeterministic dataflow. Profunctors are shown to play a key role in relating models for concurrency and to support an interpretation as higherorder processes (where input and output may be processes). Two recent directions of research are described. One is concerned with a language and computational interpretation for profunctors. This addresses the duality between input and output in profunctors. The other is to investigate general spans of event structures (the spans can be viewed as special profunctors) to give causal semantics to higherorder processes. For this it is useful to generalise event structures to allow events which “persist.”
Regular Types for Active Objects
, 1993
"... Previous work on typetheoretic foundations for objectoriented programming languages has mostly focused on applying or extending functional type theory to functional "objects." This approach, while benefiting from a vast body of existing literature, has the disadvantage of dealing with st ..."
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Cited by 208 (5 self)
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Previous work on typetheoretic foundations for objectoriented programming languages has mostly focused on applying or extending functional type theory to functional "objects." This approach, while benefiting from a vast body of existing literature, has the disadvantage of dealing with state change either in a roundabout way or not at all, and completely sidestepping issues of concurrency. In particular, dynamic issues of nonuniform service availability and conformance to protocols are not addressed by functional types. We propose a new type framework that characterizes objects as regular (finite state) processes that provide guarantees of service along public channels. We also propose a new notion of subtyping for active objects, based on Brinksma's notion of extension, that extends Wegner and Zdonik's "principle of substitutability" to nonuniform service availability. Finally, we formalize what it means to "satisfy a client's expectations," and we show how regular types canbe used...
Multiprocessor and Distributed System Design: The Integration of Functional Specification and Performance Analysis Using Stochastic Process Algebras
, 1993
"... We introduce Stochastic Process Algebras as a novel approach for the structured design and analysis of both the functional behaviour and performance characteristics of parallel and distributed systems. This is achieved by integrating performance modelling and analysis into the powerful and well i ..."
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Cited by 138 (17 self)
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We introduce Stochastic Process Algebras as a novel approach for the structured design and analysis of both the functional behaviour and performance characteristics of parallel and distributed systems. This is achieved by integrating performance modelling and analysis into the powerful and well investigated formal description technique of process algebras. After advocating the use of stochastic process algebras as a modelling technique we recapitulate the foundations of classical process algebras. Then we present extensions of process algebras such that the requirements of performance analysis are taken into account. Examples illustrate the methodological advantages that are gained.
Modal logics for mobile processes
 Theoretical Computer Science
, 1993
"... In process algebras, bisimulation equivalence is typically dened directly in terms of the operational rules of action � it also has an alternative characterization in terms of a simple modal logic (sometimes called HennessyMilner logic). This paper rst de nes two forms of bisimulation equivalence ..."
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Cited by 128 (4 self)
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In process algebras, bisimulation equivalence is typically dened directly in terms of the operational rules of action � it also has an alternative characterization in terms of a simple modal logic (sometimes called HennessyMilner logic). This paper rst de nes two forms of bisimulation equivalence for thecalculus, a process algebra which allows dynamic recon guration among processes � it then explores a family of possible logics, with di erent modaloperators. It is proven that two of these logics characterize the two bisimulation equivalences. Also, the relative expressive power of all the logics is exhibited as a lattice. The results are applicable to most valuepassing process algebras. 1
A Classification of Security Properties for Process Algebras
 JOURNAL OF COMPUTER SECURITY
, 1994
"... Several information flow security definitions, proposed in the literature, are generalized and adapted to the model of labelled transition systems. This very general model has been widely used as a semantic domain for many process algebras, e.g. CCS. As a byproduct, we provide a process algebra sim ..."
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Cited by 127 (16 self)
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Several information flow security definitions, proposed in the literature, are generalized and adapted to the model of labelled transition systems. This very general model has been widely used as a semantic domain for many process algebras, e.g. CCS. As a byproduct, we provide a process algebra similar to CCS with a set of security notions, hence relating these two areas of concurrency research. A classification of these generalized security definitions is presented, taking into account also the additional property of input totality, which can influence this taxonomy. We also show that some of these security properties are composable w.r.t. the operators of parallelism and action restriction.
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.