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Pure bigraphs: structure and dynamics
, 2005
"... Bigraphs are graphs whose nodes may be nested, representing locality, independently of the edges connecting them. They may be equipped with reaction rules, forming a bigraphical reactive system (Brs) in which bigraphs can reconfigure themselves. Following an earlier paper describing link graphs, a c ..."
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Cited by 50 (5 self)
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Bigraphs are graphs whose nodes may be nested, representing locality, independently of the edges connecting them. They may be equipped with reaction rules, forming a bigraphical reactive system (Brs) in which bigraphs can reconfigure themselves. Following an earlier paper describing link graphs, a constituent of bigraphs, this paper is a devoted to pure bigraphs, which in turn underlie various more refined forms. Elsewhere it is shown that behavioural analysis for Petri nets, πcalculus and mobile ambients can all be recovered in the uniform framework of bigraphs. The paper first develops the dynamic theory of an abstract structure, a wide reactive system (Wrs), of which a Brs is an instance. In this context, labelled transitions are defined in such a way that the induced bisimilarity is a congruence. This work is then specialised to Brss, whose graphical structure allows many refinements of the theory. The latter part of the paper emphasizes bigraphical theory that is relevant to the treatment of dynamics via labelled transitions. As a running example, the theory is applied to finite pure CCS, whose resulting transition system and bisimilarity are analysed in detail. The paper also mentions briefly the use of bigraphs to model pervasive computing and
Basic Observables for a Calculus for Global Computing
, 2004
"... We develop the semantic theory of a foundational language for modelling applications over global computers whose interconnection structure can be explicitly manipulated. Together with process distribution, process mobility and remote asynchronous communication through distributed data repositories, ..."
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Cited by 13 (6 self)
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We develop the semantic theory of a foundational language for modelling applications over global computers whose interconnection structure can be explicitly manipulated. Together with process distribution, process mobility and remote asynchronous communication through distributed data repositories, the language provides constructs for explicitly modelling internode connections and for dynamically activating and deactivating them. For the proposed language, we define natural notions of extensional observations and study their closure under operational reductions and/or language contexts to obtain barbed congruence and may testing equivalence. For such equivalences, we provide alternative characterizations in terms of a labelled bisimulation and a trace equivalence that can be used for actual proofs. We discuss how the language and its theory can be extended to include more sophisticated features that enable a finer control on the activation of connections. To asses practical usability of the semantic theory, we model a scenario for communications between mobile devices and use the introduced proof techniques to analyze it and verify some relevant properties.
Profunctors, open maps and bisimulation
 Mathematical Structures in Computer Science, To appear. Available from the Glynn Winskel’s web
, 2000
"... ..."
Behavioural Theory for Mobile Ambients
 In: Proceedings of the 3rd International Conference on Theoretical Computer Science (IFIP TCS
, 2004
"... We study a behavioural theory of Mobile Ambients, a process calculus for modelling mobile agents in widearea networks, focussing on reduction barbed congruence. Our contribution is threefold. (1) We prove a context lemma which shows that only parallel and nesting contexts need be examined to recove ..."
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Cited by 12 (1 self)
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We study a behavioural theory of Mobile Ambients, a process calculus for modelling mobile agents in widearea networks, focussing on reduction barbed congruence. Our contribution is threefold. (1) We prove a context lemma which shows that only parallel and nesting contexts need be examined to recover this congruence. (2) We characterise this congruence using a labelled bisimilarity: this requires novel techniques to deal with asynchronous movements of agents and with the invisibility of migrations of secret locations. (3) We develop refined proof methods involving upto proof techniques, which allow us to verify a set of algebraic laws and the correctness of more complex examples.
A bisimulationbased semantic theory of safe ambients
 ACM Transactions on Programming Languages and Systems
, 2006
"... We develop a semantics theory for SAP, a variant of Levi and Sangiorgi’s Safe Ambients, SA. The dynamics of SA relies upon capabilities (and cocapabilities) exercised by mobile agents, called ambients, to interact with each other. These capabilities contain references, the names of ambients with wh ..."
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Cited by 11 (0 self)
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We develop a semantics theory for SAP, a variant of Levi and Sangiorgi’s Safe Ambients, SA. The dynamics of SA relies upon capabilities (and cocapabilities) exercised by mobile agents, called ambients, to interact with each other. These capabilities contain references, the names of ambients with which they wish to interact. In SAP we generalise the notion of capability: in order to interact with an ambient n, an ambient m must exercise a capability indicating both n and a password h to access n; the interaction between n and m takes place only if n is willing to perform a corresponding cocapability with the same password h. The name h can also be looked upon as a port to access ambient n via port h. In SAP by managing passwords/ports, for example generating new ones and distributing them selectively, an ambient may now program who may migrate into its computation space, and when. Moreover in SAP an ambient may provide different services/resources depending on the port accessed by the incoming clients. Then, we give an ltsbased operational semantics for SAP and a labelled bisimulation equivalence which is proved to coincide with reduction barbed congruence. We use our notion of bisimulation to prove a set of algebraic laws which are subsequently exploited to prove more significant examples.
Reduction Semantics for Ambient Calculi
 Trans In) (Trans Cap) P ≻ (ν−→ p )〈M.P ′ 〉P ′′ P M −→CG (ν −→ p )(P ′ P ′′ ) (fn(M) ∩ −→ p = ∅) (Trans Amb) P
, 2004
"... First of all, I would like to thank my supervisor Dr. Iain C. C. Phillips, for his support and collaboration during this period of research. I thank Iain for having taught me to be more precise and sharp, and for long, detailed and inspiring discussions on the topic of this dissertation. Finally I t ..."
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Cited by 8 (5 self)
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First of all, I would like to thank my supervisor Dr. Iain C. C. Phillips, for his support and collaboration during this period of research. I thank Iain for having taught me to be more precise and sharp, and for long, detailed and inspiring discussions on the topic of this dissertation. Finally I thank him for his enormous patience towards my stubbornness. I would like to thank Dr. Nobuko Yoshida for many useful discussions and for being very supportive and positive about my work. To Sergio Maffeis go thanks for many discussions on various subjects of research and philosophy during the last two years at Imperial College. He suggested an improvement to the solution for the leader election problem for the Ambient Calculus. I would like to thank also Andrew Phillips, and the concurrency group at Imperial for the Monday lunch meetings. This has been a wonderful forum for discussing various aspects of my work. I like to thank Prof. Chris Hankin and Dr. Sophia Drossopoulou for helping me on various occasions with administrative problems and (especially Chris) for supporting most of my travelling. I do not know how I could have ever achieved this without my husband, Steffen van Bakel. He
Confining Data and Processes in Global Computing Applications
 Science of Computer Programming
, 2004
"... A programming notation is introduced that can be used for protecting secrecy and integrity of data in global computing applications. The approach is based on the explicit annotations of data and network nodes. Data are tagged with information about the allowed movements, while network nodes are t ..."
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Cited by 6 (3 self)
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A programming notation is introduced that can be used for protecting secrecy and integrity of data in global computing applications. The approach is based on the explicit annotations of data and network nodes. Data are tagged with information about the allowed movements, while network nodes are tagged with information about which nodes can send data and spawn processes over them. These restrictions/annotations are used to confine the movement of data and processes. First, a general framework for describing global computing applications is proposed and the issues related to confinement are discussed in such a context. Then, the general framework is instantiated onto three models for process interaction and mobility, namely cKlaim (the kernel of Klaim), D# (a distributed version of the #calculus) and M (a variant of the Mobile Ambient Calculus). For all of these formalisms, it is shown that their semantics guarantees that computations proceed only while respecting confinement constraints. It is proven that, after successful static type checking, data can reside at, and cross only, authorized nodes. Possible "localizations" of this property are discussed that require checking only relevant subnets. Finally, the theory is used to model secure behaviours of a UNIXlike multiuser system.
Spi Calculus Translated to πCalculus Preserving May Testing
, 2003
"... We present a concise and natural encoding of the spicalculus into the more basic πcalculus and establish its correctness with respect to a formal notion of testing. This is particularly relevant for security protocols modelled in spi since the tests can be viewed as adversaries. The translation has ..."
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Cited by 4 (0 self)
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We present a concise and natural encoding of the spicalculus into the more basic πcalculus and establish its correctness with respect to a formal notion of testing. This is particularly relevant for security protocols modelled in spi since the tests can be viewed as adversaries. The translation has been implemented in a prototype tool. As a consequence, protocols can be described in the spi calculus and analysed with the emerging flora of tools already available for π. The translation also entails a more detailed operational understanding of spi since high level constructs like encryption are encoded in a well known lower level. The formal correctness proof is nontrivial and interesting in its own; so called context bisimulations and new techniques for compositionality make the proof simpler and more concise. 1
Minimization Algorithm for Symbolic Bisimilarity
, 2009
"... The operational semantics of interactive systems is usually described by labeled transition systems. Abstract semantics is defined in terms of bisimilarity that, in the finite case, can be computed via the wellknown partition refinement algorithm. However, the behaviour of interactive systems is in ..."
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Cited by 4 (2 self)
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The operational semantics of interactive systems is usually described by labeled transition systems. Abstract semantics is defined in terms of bisimilarity that, in the finite case, can be computed via the wellknown partition refinement algorithm. However, the behaviour of interactive systems is in many cases infinite and thus checking bisimilarity in this way is unfeasible. Symbolic semantics allows to define smaller, possibly finite, transition systems, by employing symbolic actions and avoiding some sources of infiniteness. Unfortunately, the standard partition refinement algorithm does not work with symbolic bisimilarity.
A Semantic Theory for Global Computing Systems
, 2004
"... We introduce cKlaim, a process calculus that can be thought of as a variant of the #calculus with process distribution, process mobility and asynchronous communication through distributed repositories. Upon it, we develop a semantic theory to reason about programs. More precisely, we introduce a ..."
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Cited by 3 (2 self)
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We introduce cKlaim, a process calculus that can be thought of as a variant of the #calculus with process distribution, process mobility and asynchronous communication through distributed repositories. Upon it, we develop a semantic theory to reason about programs. More precisely, we introduce a natural contextually defined behavioural semantics, give a coinductive characterization in terms of a labelled bisimulation and illustrate some significant laws. Then, we smoothly tune the theory to model two more concrete settings obtained by explicitly considering failures and node connections, two lowlevel features that in real life can a#ect the underlying network infrastructure and, hence, the ability of processes to perform remote operations.