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23
The Seal Calculus
, 2005
"... The Seal Calculus is a process language for describing mobile computation. Threads and resources are tree structured; the nodes thereof correspond to agents, the units of mobility. The Calculus extends a �calculus core with synchronous, objective mobility of agents over channels. This paper syste ..."
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Cited by 24 (0 self)
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The Seal Calculus is a process language for describing mobile computation. Threads and resources are tree structured; the nodes thereof correspond to agents, the units of mobility. The Calculus extends a �calculus core with synchronous, objective mobility of agents over channels. This paper systematically compares all previous variants of Seal Calculus. We study their operational behaviour with labelled transition systems and bisimulations; by comparing the resulting algebraic theories we highlight the differences between these apparently similar approaches. This leads us to identify the dialect of Seal that is most amenable to operational reasoning and can form the basis of a distributed programming language. We propose type systems for characterising the communications in which an agent can engage. The type systems thus enforce a discipline of agent mobility, since the latter is coded in terms of higherorder communication.
The Seal Calculus Revisited: contextual equivalence and bisimilarity
, 2003
"... We present a new version of the Seal Calculus, a calculus of mobile computation. We study observational congruence and bisimulation theory, and show how they are related. ..."
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Cited by 23 (3 self)
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We present a new version of the Seal Calculus, a calculus of mobile computation. We study observational congruence and bisimulation theory, and show how they are related.
Modelling dynamic Web data
 Imperial College London
, 2003
"... We introduce the Xdπ calculus, a peertopeer model for reasoning about dynamic web data. Web data is not just stored statically. Rather it is referenced indirectly, for example using hyperlinks, service calls, or scripts for dynamically accessing data, which require the complex coordination of data ..."
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Cited by 22 (3 self)
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We introduce the Xdπ calculus, a peertopeer model for reasoning about dynamic web data. Web data is not just stored statically. Rather it is referenced indirectly, for example using hyperlinks, service calls, or scripts for dynamically accessing data, which require the complex coordination of data and processes between sites. The Xdπ calculus models this coordination, by integrating the XML data structure with process orchestration techniques associated with the distributed picalculus. We study behavioural equivalences for Xdπ, to analyze the various possible patterns of data and process interaction.
Bisimulation Proof Methods for Mobile Ambients
 IN PROC. OF ICALP’03, VOLUME 2719 OF LNCS
, 2003
"... We study the behavioural theory of Cardelli and Gordon's Mobile Ambients. We give an LTS based operational semantics, and a labelled bisimulation based equivalence that coincides with reduction barbed congruence. We also provide two upto proof techniques that we use to prove a set of algebraic laws ..."
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Cited by 19 (3 self)
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We study the behavioural theory of Cardelli and Gordon's Mobile Ambients. We give an LTS based operational semantics, and a labelled bisimulation based equivalence that coincides with reduction barbed congruence. We also provide two upto proof techniques that we use to prove a set of algebraic laws, including the perfect firewall equation.
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.
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.
Locating Reaction with 2categories
, 2004
"... Groupoidal relative pushouts (GRPOs) have recently been proposed by the authors as a new foundation for Leifer and Milner's approach to deriving labelled bisimulation congruences from reduction systems. In this paper, we develop the theory of GRPOs further, proving that wellknown equivalences, othe ..."
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Cited by 11 (1 self)
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Groupoidal relative pushouts (GRPOs) have recently been proposed by the authors as a new foundation for Leifer and Milner's approach to deriving labelled bisimulation congruences from reduction systems. In this paper, we develop the theory of GRPOs further, proving that wellknown equivalences, other than bisimulation, are congruences. To demonstrate the type of category theoretic arguments which are inherent in the 2categorical approach, we construct GRPOs in a category of `bunches and wirings.' Finally, we prove that the 2categorical theory of GRPOs is a generalisation of the approaches based on Milner's precategories and Leifer's functorial reactive systems.
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.
A Calculus of Bounded Capacities
 In ASIAN’03, number 2896 in LNCS
, 2003
"... Resource control has attracted increasing interest in foundational research on distributed systems. This paper focuses on space control and develops an analysis of space usage in the context of an ambientlike calculus with bounded capacities and weighed processes, where migration and activation ..."
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Cited by 7 (1 self)
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Resource control has attracted increasing interest in foundational research on distributed systems. This paper focuses on space control and develops an analysis of space usage in the context of an ambientlike calculus with bounded capacities and weighed processes, where migration and activation require space.
Ambient Calculi with Types: a Tutorial
 Global Computing  Programming Environments, Languages, Security and Analysis of Systems, volume 2874 of LNCS
, 2003
"... A tutorial introduction to the key concepts of ambient calculi and their type disciplines, illustrated through a number of systems proposed in the last few years, such as Mobile Ambients, Safe Ambients, Boxed Ambients, and other related calculi with types. ..."
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Cited by 6 (2 self)
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A tutorial introduction to the key concepts of ambient calculi and their type disciplines, illustrated through a number of systems proposed in the last few years, such as Mobile Ambients, Safe Ambients, Boxed Ambients, and other related calculi with types.