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A calculus for orchestration of web services
 LECTURE NOTES IN COMPUTER SCIENCE
, 2007
"... We introduce COWS (Calculus for Orchestration of Web Services), a new foundational language for SOC whose design has been inﬂuenced by WSBPEL, the de facto standard language for orchestration of web services.
COWS combines in an original way a number of ingredients borrowed from wellknown process ..."
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Cited by 46 (12 self)
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We introduce COWS (Calculus for Orchestration of Web Services), a new foundational language for SOC whose design has been inﬂuenced by WSBPEL, the de facto standard language for orchestration of web services.
COWS combines in an original way a number of ingredients borrowed from wellknown process calculi, e.g. asynchronous communication, polyadic synchronization, pattern matching, protection, delimited receiving and killing activities, while resulting diﬀerent from any of them. Several examples illustrates COWS peculiarities and show its expressiveness both for modelling imperative and orchestration constructs, e.g. web services, ﬂow graphs, fault and compensation handlers, and for encoding other process and orchestration languages.
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 23 (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.
Electoral systems in ambient calculi
 In Proceedings of 7th International Conference on Foundations of Software Science and Computation Structures, FoSSaCS 2004
, 2004
"... Abstract. This paper compares the expressiveness of ambient calculi against different dialects of the picalculus. Cardelli and Gordon encoded the asynchronous picalculus into their calculus of Mobile Ambients (MA). Zimmer has shown that the synchronous picalculus without choice can be encoded in ..."
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Cited by 18 (7 self)
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Abstract. This paper compares the expressiveness of ambient calculi against different dialects of the picalculus. Cardelli and Gordon encoded the asynchronous picalculus into their calculus of Mobile Ambients (MA). Zimmer has shown that the synchronous picalculus without choice can be encoded in pure (no communication) Safe Ambients. We show that pure MA without restriction has symmetric electoral systems, that is, it is possible to solve the problem of electing a leader in a symmetric network. By the work of Palamidessi, this implies that pure MA without restriction is not encodable (under certain conditions) in the picalculus with separate choice. We adapt the work of Carbone and Maffeis to show that pure MA cannot be encoded (under certain other conditions) into the picalculus with mixed choice (but without matching). 1
Bigraphical Semantics of HigherOrder Mobile Embedded Resources with Local Names
 Proceedings of the Graph Transformation for Verification and Concurrency workshop (GTVC'05)
, 2006
"... Bigraphs have been introduced with the aim to provide a topographical metamodel for mobile, distributed agents that can manipulate their own linkages and nested locations, generalising both characteristics of the πcalculus and the Mobile Ambients calculus. We give the first bigraphical presentatio ..."
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Cited by 17 (10 self)
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Bigraphs have been introduced with the aim to provide a topographical metamodel for mobile, distributed agents that can manipulate their own linkages and nested locations, generalising both characteristics of the πcalculus and the Mobile Ambients calculus. We give the first bigraphical presentation of a nonlinear, higherorder process calculus with nested locations, nonlinear active process mobility, and local names, the calculus of HigherOrder Mobile Embedded Resources (Homer). The presentation is based on Milner’s recent presentation of the λcalculus in local bigraphs. The combination of nonlinear active process mobility and local names requires a new definition of parametric reaction rules and a representation of the location of names. We suggest localised bigraphs as a generalisation of local bigraphs in which links can be further localised. Key words: bigraphs, local names, nonlinear process mobility
Psicalculi: Mobile processes, nominal data, and logic
 In Proceedings of LICS 2009
"... A psicalculus is an extension of the picalculus with nominal data types for data structures and for logical assertions representing facts about data. These can be transmitted between processes and their names can be statically scoped using the standard picalculus mechanism to allow for scope migr ..."
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Cited by 16 (8 self)
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A psicalculus is an extension of the picalculus with nominal data types for data structures and for logical assertions representing facts about data. These can be transmitted between processes and their names can be statically scoped using the standard picalculus mechanism to allow for scope migrations. Other proposed extensions of the picalculus can be formulated as psicalculi; examples include the applied picalculus, the spicalculus, the fusion calculus, the concurrent constraint picalculus, and calculi with polyadic communication channels or pattern matching. Psicalculi can be even more general, for example by allowing structured channels, higherorder formalisms such as the lambda calculus for data structures, and a predicate logic for assertions. Our labelled operational semantics and definition of bisimulation is straightforward, without a structural congruence. We establish minimal requirements on the nominal data and logic in order to prove general algebraic properties of psicalculi. The proofs have been checked in the interactive proof checker Isabelle. We are the first to formulate a truly compositional labelled operational semantics for calculi of this calibre. Expressiveness and therefore modelling convenience significantly exceeds that of other formalisms, while the purity of the semantics is on par with the original picalculus. 1
PsiCalculi in Isabelle
 In Proc of the 22nd Conference on Theorem Proving in Higher Order Logics (TPHOLs), volume 5674 of LNCS
"... Abstract. Psicalculi are extensions of the picalculus, accommodating arbitrary nominal datatypes to represent not only data but also communication channels, assertions and conditions, giving it an expressive power beyond the applied picalculus and the concurrent constraint picalculus. We have for ..."
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Cited by 11 (4 self)
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Abstract. Psicalculi are extensions of the picalculus, accommodating arbitrary nominal datatypes to represent not only data but also communication channels, assertions and conditions, giving it an expressive power beyond the applied picalculus and the concurrent constraint picalculus. We have formalised psicalculi in the interactive theorem prover Isabelle using its nominal datatype package. One distinctive feature is that the framework needs to treat binding sequences, as opposed to single binders, in an efficient way. While different methods for formalising single binder calculi have been proposed over the last decades, representations for such binding sequences are not very well explored. The main effort in the formalisation is to keep the machine checked proofs as close to their penandpaper counterparts as possible. We discuss two approaches to reasoning about binding sequences along with their strengths and weaknesses. We also cover custom induction rules to remove the bulk of manual alphaconversions. 1
A Calculus for Trust Management
 In Proceedings from Foundations of Software Technology and Theoretical Computer Science: 24th International Conference (FSTTCS’04
, 2004
"... We introduce ctm, a process calculus which embodies a notion of trust for global computing systems. In ctm each principal (location) is equipped with a policy, which determines its legal behaviour, and with a protocol, which allows interactions between principals and the flow of information from ..."
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Cited by 9 (6 self)
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We introduce ctm, a process calculus which embodies a notion of trust for global computing systems. In ctm each principal (location) is equipped with a policy, which determines its legal behaviour, and with a protocol, which allows interactions between principals and the flow of information from principals to policies. We elect to formalise policies using a Dataloglike logic, and to express protocols in the process algebra style. This yields an expressive calculus very suitable for the global computing scenarios, and provides a formalisation of notions such as trust evolution. For ctm we define barbed equivalences and study their possible applications.
Behavioural Equivalences for Dynamic Web Data
, 2004
"... We study behavioural equivalences for dynamic web data in Xd#, a model for reasoning about behaviour found in (for example) dynamic web page programming, applet interaction, and webservice orchestration. Xd# is based on an idealised model of semistructured data, and an extension of the #calculus ..."
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Cited by 6 (3 self)
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We study behavioural equivalences for dynamic web data in Xd#, a model for reasoning about behaviour found in (for example) dynamic web page programming, applet interaction, and webservice orchestration. Xd# is based on an idealised model of semistructured data, and an extension of the #calculus with locations and operations for interacting with data. The equivalences are nonstandard due to the integration of data and processes, and the presence of locations. Contents 1
Dynamic Web Data: A Process Algebraic Approach
, 2005
"... Peer to peer systems, exchanging dynamic documents through Web services, are a simple and effective platform for data integration on the internet. Dynamic documents can contain both data and references to external sources in the form of links, calls to web services, or coordination scripts. XML stan ..."
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Cited by 5 (1 self)
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Peer to peer systems, exchanging dynamic documents through Web services, are a simple and effective platform for data integration on the internet. Dynamic documents can contain both data and references to external sources in the form of links, calls to web services, or coordination scripts. XML standards, and industrial platforms for web services, provide the technological basis for building such systems. We argue that process algebras are a promising tool for studying and understanding their formal properties. In this thesis, we define the Xdπcalculus with the aim of reasoning about dynamic Web data. Xdπ terms represent networks of peers, each consisting of an XML data repository and a working space where processes are allowed to run. Processes, inspired by the πcalculus, can communicate with each other, query and update the local repository, or migrate to other peers to continue execution. Data can contain scripted processes, which can be executed by other processes. For example, Xdπ processes can be used to embed service calls in documents and to model Web services. We investigate behavioural equivalences for Xdπ, comparing several observable
Comparing calculi for mobility via their relative expressive power
"... In this paper, we comparatively analyze some mainstream calculi for mobility: asynchronous πcalculus, distributed πcalculus, a distributed version of Linda and Mobile/Boxed/Safe ambients. In particular, we focus on their relative expressive power, i.e. we try to encode one in the other while respe ..."
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Cited by 5 (3 self)
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In this paper, we comparatively analyze some mainstream calculi for mobility: asynchronous πcalculus, distributed πcalculus, a distributed version of Linda and Mobile/Boxed/Safe ambients. In particular, we focus on their relative expressive power, i.e. we try to encode one in the other while respecting some reasonable properties. According to the possibility or the impossibility for such results, we set up a hierarchy of these languages. Finally, we discuss and compare some variants of ambientlike languages, including objective moves, passwords and different semantics for the mobility primitives and for parentchild communications.