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305
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.”
Detecting Causal Relationships in Distributed Computations: In Search of the Holy Grail
 In search of the holy grail. Distributed Computing
, 1994
"... : The paper shows that characterizing the causal relationship between significant events is an important but nontrivial aspect for understanding the behavior of distributed programs. An introduction to the notion of causality and its relation to logical time is given; some fundamental results conce ..."
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Cited by 231 (4 self)
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: The paper shows that characterizing the causal relationship between significant events is an important but nontrivial aspect for understanding the behavior of distributed programs. An introduction to the notion of causality and its relation to logical time is given; some fundamental results concerning the characterization of causality are presented. Recent work on the detection of causal relationships in distributed computations is surveyed. The issue of observing distributed computations in a causally consistent way and the basic problems of detecting global predicates are discussed. To illustrate the major difficulties, some typical monitoring and debugging approaches are assessed, and it is demonstrated how their feasibility is severely limited by the fundamental problem to master the complexity of causal relationships. Keywords: Distributed Computation, Causality, Distributed System, Causal Ordering, Logical Time, Vector Time, Global Predicate Detection, Distributed Debugging, ...
Rulebased Modelling of Cellular Signalling
 PROCEEDINGS OF THE 18 TH INTERNATIONAL CONFERENCE ON CONCURRENCY THEORY (CONCUR’07), LECTURE NOTES IN COMPUTER SCIENCE
, 2007
"... Modelling is becoming a necessity in studying biological signalling pathways, because the combinatorial complexity of such systems rapidly overwhelms intuitive and qualitative forms of reasoning. Yet, this same combinatorial explosion makes the traditional modelling paradigm based on systems of di ..."
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Cited by 107 (22 self)
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Modelling is becoming a necessity in studying biological signalling pathways, because the combinatorial complexity of such systems rapidly overwhelms intuitive and qualitative forms of reasoning. Yet, this same combinatorial explosion makes the traditional modelling paradigm based on systems of differential equations impractical. In contrast, agentbased or concurrent languages, such as κ [1–3] or the closely related BioNetGen language [4–10], describe biological interactions in terms of rules, thereby avoiding the combinatorial explosion besetting differential equations. Rules are expressed in an intuitive graphical form that transparently represents biological knowledge. In this way, rules become a natural unit of model building, modification, and discussion. We illustrate this with a sizeable example obtained from refactoring two models of EGF receptor signalling that are based on differential equations [11, 12]. An exciting aspect of the agentbased approach is that it naturally lends itself to the identification and analysis of the causal structures that deeply shape the dynamical, and perhaps even evolutionary, characteristics of complex distributed biological systems. In particular, one can adapt the notions of causality and conflict, familiar from concurrency theory, to κ, our representation language of choice. Using the EGF receptor model as an example, we show how causality enables the formalization of the colloquial concept of pathway and, perhaps more surprisingly, how conflict can be used to dissect the signalling dynamics to obtain a qualitative handle on the range of system behaviours. By taming the combinatorial explosion, and exposing the causal structures and key kinetic junctures in a model, agent and rulebased representations hold promise for making modelling more powerful, more perspicuous, and of appeal to a wider audience.
Diagnosis of Asynchronous Discrete Event Systems, a Net Unfolding Approach
 IEEE TRANS. ON AUTOMATIC CONTROL
, 2001
"... In this paper we formulate asynchronous diagnosis by means of hidden state history reconstruction, from alarm observations. We follow a socalled true concurrency approach, in which no global state and no global time is available. Instead, we use only local states in combination with a partial order ..."
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Cited by 94 (30 self)
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In this paper we formulate asynchronous diagnosis by means of hidden state history reconstruction, from alarm observations. We follow a socalled true concurrency approach, in which no global state and no global time is available. Instead, we use only local states in combination with a partial order model of time, in which local events are ordered if they are either generated on the same site, or related via some causality relation. Our basic mathematical tool is that of net unfoldings originating from the Petri net research area. This study was motivated by the problem of event correlation in telecommunications network management.
Synthesis of Timed Asynchronous Circuits
 IEEE Transactions on VLSI Systems
, 1993
"... In this paper we present a synthesis method that utilizes timing constraints to generate timed asynchronous circuits. By unfolding the cyclic graph specification of an asynchronous circuit into an infinite acyclic graph, we are able to use efficient algorithms to analyze the given timing constraints ..."
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Cited by 87 (16 self)
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In this paper we present a synthesis method that utilizes timing constraints to generate timed asynchronous circuits. By unfolding the cyclic graph specification of an asynchronous circuit into an infinite acyclic graph, we are able to use efficient algorithms to analyze the given timing constraints. We derive a sufficient condition for the removal of redundancy in the specification. Based on this condition, we only need to analyze a finite subgraph of the infinite acyclic graph for derivation of a correct implementation. To the reduced specification, we apply a systematic synthesis procedure that further optimizes the implementation based on the timing constraints. Using realistic circuit examples, we demonstrate that the resulting timed implementation can be significantly reduced in complexity from its speedindependent counterpart while remaining hazardfree under the given timing constraints.
Events in security protocols
, 2001
"... The events of a security protocol and their causal dependency can play an important role in the analysis of security properties. This insight underlies both strand spaces and the inductive method. But neither of these approaches builds up the events of a protocol in a compositional way, so that ther ..."
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Cited by 70 (15 self)
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The events of a security protocol and their causal dependency can play an important role in the analysis of security properties. This insight underlies both strand spaces and the inductive method. But neither of these approaches builds up the events of a protocol in a compositional way, so that there is an informal spring from the protocol to its model. By broadening the models to certain kinds of Petri nets, a restricted form of contextual nets, a compositional eventbased semantics is given to an economical, but expressive, language for describing security protocols; so the events and dependency of a wide range of protocols are determined once and for all. The net semantics is formally related to a transition semantics, strand spaces and inductive rules, as well as trace languages and event structures, so unifying a range of approaches, as well as providing conditions under which particular, more limited, models are adequate for the analysis of protocols. The net semantics allows the derivation of general properties and proof principles which are demonstrated in establishing an authentication property, following a diagrammatic style of proof.
Graph Types For Monadic Mobile Processes
 University of Edinburgh
, 1996
"... . While types for name passing calculi have been studied extensively in the context of sorting of polyadic ßcalculus [5, 34, 9, 28, 32, 19, 33, 10, 17], the same type abstraction is not possible in the monadic setting, which was left as an open issue by Milner [21]. We solve this problem with an ex ..."
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Cited by 64 (8 self)
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. While types for name passing calculi have been studied extensively in the context of sorting of polyadic ßcalculus [5, 34, 9, 28, 32, 19, 33, 10, 17], the same type abstraction is not possible in the monadic setting, which was left as an open issue by Milner [21]. We solve this problem with an extension of sorting which captures dynamic aspects of process behaviour in a simple way. Equationally this results in the full abstraction of the standard encoding of polyadic ßcalculus into the monadic one: the sorted polyadic ßterms are equated by a basic behavioural equality in the polyadic calculus if and only if their encodings are equated in a basic behavioural equality in the typed monadic calculus. This is the first result of this kind we know of in the context of the encoding of polyadic name passing, which is a typical example of translation of highlevel communication structures into ß calculus. The construction is general enough to be extendable to encodings of calculi with mo...
Refinement of Actions and Equivalence Notions for Concurrent Systems
 Acta Informatica
, 1998
"... This paper combines and extends the material of [GGa/c/d/e], except for the part in [GGc] on refinement of transitions in Petri nets and the discussion of TCSPlike parallel composition in [GGe]. An informal presentation of some basic ingredients of this paper appeared as [GGb]. Among others, th ..."
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Cited by 59 (3 self)
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This paper combines and extends the material of [GGa/c/d/e], except for the part in [GGc] on refinement of transitions in Petri nets and the discussion of TCSPlike parallel composition in [GGe]. An informal presentation of some basic ingredients of this paper appeared as [GGb]. Among others, the treatment of action refinement in stable and nonstable event structures is new. The research reported here was supported by Esprit project 432 (METEOR), Esprit Basic Research Action 3148 (DEMON), Sonderforschungsbereich 342 of the TU Munchen, ONR grant N0001492J1974 and the Human Capital and Mobility Cooperation Network EXPRESS (Expressiveness of Languages for Concurrency). Contents
The semantics of x86CC multiprocessor machine code, POPL’09
"... Multiprocessors are now dominant, but real multiprocessors do not provide the sequentially consistent memory that is assumed by most work on semantics and verification. Instead, they have subtle relaxed (or weak) memory models, usually described only in ambiguous prose, leading to widespread confus ..."
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Cited by 54 (20 self)
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Multiprocessors are now dominant, but real multiprocessors do not provide the sequentially consistent memory that is assumed by most work on semantics and verification. Instead, they have subtle relaxed (or weak) memory models, usually described only in ambiguous prose, leading to widespread confusion. We develop a rigorous and accurate semantics for x86 multiprocessor programs, from instruction decoding to relaxed memory model, mechanised in HOL. We test the semantics against actual processors and the vendor litmustest examples, and give an equivalent abstractmachine characterisation of our axiomatic memory model. For programs that are (in some precise sense) datarace free, we prove in HOL that their behaviour is sequentially consistent. We also contrast the x86 model with some aspects of Power and ARM behaviour. This provides a solid intuition for lowlevel programming, and a sound foundation for future work on verification, static analysis, and compilation of lowlevel concurrent code.
Configuration Structures
 Proceedings of 10th Annual IEEE Symposium on Logic in Computer Science. IEEE Computer
, 1995
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