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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
Sessions and session types: an overview
 IN 6TH INTERNATIONAL WORKSHOP ON WEB SERVICES AND FORMAL METHODS (WSFM’09
, 2010
"... We illustrate the concepts of sessions and session types as they have been developed in the setting of the πcalculus. Motivated by the goal of obtaining a formalisation closer to existing standards and aiming at their enhancement and strengthening, several extensions of the original core system h ..."
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Cited by 14 (4 self)
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We illustrate the concepts of sessions and session types as they have been developed in the setting of the πcalculus. Motivated by the goal of obtaining a formalisation closer to existing standards and aiming at their enhancement and strengthening, several extensions of the original core system have been proposed, which we survey together with the embodying of sessions into functional and objectoriented languages, as well as some implementations.
A theory of designbycontract for distributed multiparty interactions
 In CONCUR 2010, LNCS
, 2011
"... Abstract. The approach known as Design by Contract (DbC) [23] promotes reliable software development through elaboration of type signatures for sequential programs with logical formulae. This paper presents an assertion method which generalises the notion of DbC to multiparty distributed interaction ..."
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Cited by 13 (7 self)
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Abstract. The approach known as Design by Contract (DbC) [23] promotes reliable software development through elaboration of type signatures for sequential programs with logical formulae. This paper presents an assertion method which generalises the notion of DbC to multiparty distributed interactions, enabling the specification and verification of distributed multiparty protocols, based on the πcalculus with full recursion. Centring on the notion of global assertions and their projections onto endpoint assertions, our method allows fully general specifications for typed sessions with session channel passing, constraining the content of the exchanged messages, the choice of subconversations to follow, and invariants on recursions. The paper presents key theoretical foundations of this framework, including a validation algorithm for consistency of global assertions and a sound and relatively complete compositional proof system for verifying a large class of processes against assertions. 1
Open Bisimulation for the Concurrent Constraint Picalculus ⋆
"... Abstract. The concurrent constraint picalculus (ccpicalculus) has been introduced as a model for concluding Service Level Agreements. The ccpi calculus combines the synchronous communication paradigm of process calculi with the constraint handling mechanism of concurrent constraint programming. ..."
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Cited by 11 (0 self)
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Abstract. The concurrent constraint picalculus (ccpicalculus) has been introduced as a model for concluding Service Level Agreements. The ccpi calculus combines the synchronous communication paradigm of process calculi with the constraint handling mechanism of concurrent constraint programming. While in the original presentation of the calculus a reduction semantics has been proposed, in this work we investigate the abstract semantics of ccpi processes. First, we define a labelled transition system of the calculus and a notion of open bisimilarity à la picalculus that is proved to be a congruence. Next, we give a symbolic characterisation of bisimulation and we prove that the two semantics coincide. Essentially, two processes are open bisimilar if they have the same stores of constraints this can be statically checked and if their moves can be mutually simulated. A key idea of the symbolic transition system is to have ‘contextual ’ labels, i.e. labels specifying that a process can evolve only in presence of certain constraints. Finally, we show that the polyadic Explicit Fusions calculus introduced by Gardner and Wischik can be translated into monadic ccpi and that such a transition preserves open bisimilarity. The mapping exploits fusions and tuple unifications as constraints. 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 Probabilistic Applied Pi–Calculus
, 2007
"... We propose an extension of the Applied Pi–calculus by introducing nondeterministic and probabilistic choice operators. The semantics of the resulting model, in which probability and nondeterminism are combined, is given by Segala’s Probabilistic Automata driven by schedulers which resolve the nonde ..."
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Cited by 10 (0 self)
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We propose an extension of the Applied Pi–calculus by introducing nondeterministic and probabilistic choice operators. The semantics of the resulting model, in which probability and nondeterminism are combined, is given by Segala’s Probabilistic Automata driven by schedulers which resolve the nondeterministic choice among the probability distributions over target states. Notions of static and observational equivalence are given for the enriched calculus. In order to model the possible interaction of a process with its surrounding environment a labeled semantics is given together with a notion of weak bisimulation which is shown to coincide with the observational equivalence. Finally, we prove that results in the probabilistic framework are preserved in a purely nondeterministic setting.
PSICALCULI: A FRAMEWORK FOR MOBILE PROCESSES WITH NOMINAL DATA AND LOGIC
"... Abstract. The framework of psicalculi extends the picalculus with nominal datatypes for data structures and for logical assertions and conditions. These can be transmitted between processes and their names can be statically scoped as in the standard picalculus. Psicalculi can capture the same ph ..."
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Cited by 10 (5 self)
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Abstract. The framework of psicalculi extends the picalculus with nominal datatypes for data structures and for logical assertions and conditions. These can be transmitted between processes and their names can be statically scoped as in the standard picalculus. Psicalculi can capture the same phenomena as other proposed extensions of the picalculus such as 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 predicate logic for assertions. We provide ample comparisons to related calculi and discuss a few significant applications. 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, all of which have been checked in the interactive theorem prover Isabelle. Expressiveness of psicalculi significantly exceeds that of other formalisms, while the purity of the semantics is on par with the original picalculus. 1.
StPowla: SOA, Policies and Workflows
"... Abstract. We introduce StPowla, a workflow based approach to business process modelling that integrates a simple graphical notation, to ease the presentation of the core business process, a natural policy language, Appel, to provide the necessary adaptation to the varied expectations of the various ..."
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Cited by 9 (3 self)
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Abstract. We introduce StPowla, a workflow based approach to business process modelling that integrates a simple graphical notation, to ease the presentation of the core business process, a natural policy language, Appel, to provide the necessary adaptation to the varied expectations of the various business stakeholders, and the Service Oriented Architecture, to assemble and orchestrate available services in the business process. We illustrate the approach with a loan approval process. 1
Abstract Semantics by Observable Contexts
, 2008
"... The operational behavior of interactive systems is usually given in terms of transition systems labeled with actions, which, when visible, represent both observations and interactions with the external world. The abstract semantics is given in terms of behavioral equivalences, which depend on the ac ..."
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Cited by 9 (3 self)
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The operational behavior of interactive systems is usually given in terms of transition systems labeled with actions, which, when visible, represent both observations and interactions with the external world. The abstract semantics is given in terms of behavioral equivalences, which depend on the action labels and on the amount of branching structure considered. Behavioural equivalences are often congruences with respect to the operations of the language, and this property expresses the compositionality of the abstract semantics. A simpler approach, inspired by classical formalisms like λcalculus, Petri nets, term and graph rewriting, and pioneered by the Chemical Abstract Machine [1], defines operational semantics by means of structural axioms and reaction rules. Process calculi representing complex systems, in particular those able to generate and communicate names, are often defined in this way, since structural axioms give a clear idea of the intended structure of the states while reaction rules, which are often nonconditional, give a direct account of the possible steps. Transitions caused by reaction rules, however, are not labeled, since
A fuzzy approach for negotiating quality of services
 In: Proceedings of the 2nd Symposium on Trustworthy Global Computing (TGC 2006). Volume 4661 of Lecture Notes in Computer Science
, 2007
"... Abstract. A central point when integrating services concerns to the description, agreement and enforcement of the quality aspect of service interaction, usually known as Service Level Agreement (SLA). This paper presents a framework for SLA negotiation based on fuzzy sets. We propose (i) a request l ..."
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Cited by 5 (2 self)
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Abstract. A central point when integrating services concerns to the description, agreement and enforcement of the quality aspect of service interaction, usually known as Service Level Agreement (SLA). This paper presents a framework for SLA negotiation based on fuzzy sets. We propose (i) a request language for clients to describe quality preferences, (ii) a publication language for providers to define the qualities of their offered services, and (iii) a decision procedure for granting any client request with a SLA contract fitting the requestor requirements. We start with a restricted framework in which the different qualities of a service are handled independently (as being orthogonal) and then we propose an extension that allows clients and providers to express dependencies among different qualities. 1