We compare the first-order and the higher-order paradigms for the representation of mobility in process algebras. The prototypical calculus in the first-order paradigm is the π-calculus. By generalising its sort mechanism we derive an !-order extension, called Higher-Order π-calculus (HOπ). We give examples of its use, including the encoding of -calculus. Surprisingly, we show that such an extension does not add expressiveness: Higher-order processes can be faithfully represented at first order. We conclude that the first-order paradigm, which enjoys a simpler and more intuitive theory, should be taken as basic. Nevertheless, the study of the -calculus encodings shows that a higher-order calculus can be very useful for reasoning at a more abstract level.

In 1981 Structural Operational Semantics (SOS) was introduced as a systematic way to define operational semantics of programming languages by a set of rules of a certain shape [62]. Subsequently, the format of SOS rules became the object of study. Using so-called Transition System Specifications (TSS’s) several authors syntactically restricted the format of rules and showed several useful properties about the semantics induced by any TSS adhering to the format. This has resulted in a line of research proposing several syntactical rule formats and associated meta-theorems. Properties that are guaranteed by such rule formats range from well-definedness of the operational semantics and compositionality of behavioral equivalences to security- and probability-related issues. In this paper, we provide an initial hierarchy of SOS rules formats and meta-theorems formulated around them.

The aim of this thesis is to describe the semantics of a process calculus by means of hypergraph rewriting, creating a specification mechanism combining modularity of process calculi and locality of graph transformation. Verification of processes is addressed by presenting two methods: barbed congruence for relating processes displaying the same behaviour and generic type systems, forming a central part of this work. Based on existing work in graph rewriting...

In 1981 Structural Operational Semantics (SOS) was introduced as a systematic way to define operational semantics of programming languages by a set of rules of a certain shape [G.D. Plotkin, A structural approach to operational semantics, Technical

We study a relationship between logic and computation via concurrent constraint programming. In previous papers it has been shown how a simple language for specifying asynchronous concurrent processes can be interpreted in terms of constraints. In the present paper we show that the programming interpretation via closure operators is intimately related to the logic of the constraints. More precisely we show how the usual hyperdoctrinal description of first order logic can be functorially related to another hyperdoctrine built out of closure operators. The logical connectives map onto constructions on closure operators that turn out to model programming constructs, specifically conjunction becomes parallel composition and existential quantification becomes hiding of local variables. 1 Introduction In this paper we develop a category theoretic view of the relationship between concurrent constraint programming and logic. One may think of this as an explication of the relationship between ...

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Congruence proofs for bisimulation on higher-order process calculi tend to be significantly more complex than their counterparts in first-order process algebra frameworks. Moreover, a standard technique that allows us to cover strong forms of bisimulation on higher-order calculi seems to fail for the corresponding weak forms. Similar problems are posed by applicative simulation on -calculi and our starting point is a general and elegant technique for solving them that has been invented by Howe. We adapt and extend this technique to prove two new congruence results for !-order process calculi. In the first case, where we use a static scoping discipline for action names, we treat a delay variant of late weak context bisimulation; in the second case, where we use a dynamic scoping discipline, we treat an early weak higher-order bisimulation. The present paper supersedes parts of our technical report [BF95], where we have considered second-order processes.

. We introduce an extension of -calculus, called label-selective - calculus, in which arguments of functions are selected by labels. The set of labels includes numeric positions as well as symbolic keywords. While the latter enjoy free commutation, the former must comply with relative precedence in order to preserve currying. This extension of -calculus is conservative in the sense that when the set of labels is the singleton f1g, it coincides with -calculus. The main result of this paper is that the label-selective -calculus is confluent. In other words, argument selection and reduction commute. Keywords. -Calculus, record calculus, concurrency, communication. 1 Synopsis Many modern programming languages allow specifying arguments of functions and procedures by symbolic keywords as well as using the traditional and natural numeric positions [16, 12, 4]. Symbolic keywords are usually handled as syntactic sugar and "compiled away" as numeric positions. This is made easy if the langua...

We introduce an extension of -calculus, called label-selective -calculus, in which arguments of functions are selected by labels. The set of labels includes numeric positions as well as symbolic keywords. While the latter enjoy free commutation, the former must comply with relative precedence in order to preserve currying. This extension of -calculus is conservative in the sense that when the set of labels is the singleton f1g, it coincides with -calculus. The main result of this paper is the proof that the label-selective -calculus is confluent. In other words, argument selection and reduction commute. R esum e Nous presentons une extension du -calcul, appelee -calcul label-selectif, dans laquelle les arguments des fonctions sont selectionnes par des etiquettes. L'ensemble des etiquettes comprend des positions numeriques aussi bien que des mot-clefs symboliques. Alors que ces derniers jouissent d'une commutativite libre, les premiers obeissent a une precedence relative pour preserver...

Chocs and π-calculus are two extensions of CCS where, respectively, processes and channels are transmissible values. In previous work we have proposed a formalization of the notion of bisimulation for Chocs. In this paper we suggest a more effective way to reason about this notion by means of an embedding of Chocs into a richer calculus endowed with a notion of `activation' channel which we christen Chocs t . t is the name of a new internal action which is produced by a synchronization on an activation channel, such a synchronization has the effect of forcing the execution of an idle process. In first approximation transitions in Chocs t may be understood as sequences of synchronizations along activation channels followed by an `observable' transition. There is a simple definition of bisimulation for Chocs t which satisfies natural laws and congruence rules, moreover the synchronization trees associated to Chocs t processes are finitely branching. We propose Chocs t as an intermediate ...