161 research outputs found

    Process Algebras

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    Process Algebras are mathematically rigorous languages with well defined semantics that permit describing and verifying properties of concurrent communicating systems. They can be seen as models of processes, regarded as agents that act and interact continuously with other similar agents and with their common environment. The agents may be real-world objects (even people), or they may be artifacts, embodied perhaps in computer hardware or software systems. Many different approaches (operational, denotational, algebraic) are taken for describing the meaning of processes. However, the operational approach is the reference one. By relying on the so called Structural Operational Semantics (SOS), labelled transition systems are built and composed by using the different operators of the many different process algebras. Behavioral equivalences are used to abstract from unwanted details and identify those systems that react similarly to external experiments

    Quantitative testing semantics for non-interleaving

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    This paper presents a non-interleaving denotational semantics for the ?-calculus. The basic idea is to define a notion of test where the outcome is not only whether a given process passes a given test, but also in how many different ways it can pass it. More abstractly, the set of possible outcomes for tests forms a semiring, and the set of process interpretations appears as a module over this semiring, in which basic syntactic constructs are affine operators. This notion of test leads to a trace semantics in which traces are partial orders, in the style of Mazurkiewicz traces, extended with readiness information. Our construction has standard may- and must-testing as special cases

    Independence, name-passing and constraints in models for concurrency

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    Calculi for higher order communicating systems

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    This thesis develops two Calculi for Higher Order Communicating Systems. Both calculi consider sending and receiving processes to be as fundamental as nondeterminism and parallel composition. The first calculus called CHOCS is an extension of Milner's CCS in the sense that all the constructions of CCS are included or may be derived from more fundamental constructs. Most of the mathematical framework of CCS carries over almost unchanged. The operational semantics of CHOCS is given as a labelled transition system and it is a direct extension of the semantics of CCS with value passing. A set of algebraic laws satisfied by the calculus is presented. These are similar to the CCS laws only introducing obvious extra laws for sending and receiving processes. The power of process passing is underlined by a result showing that the recursion operator is unnecessary in the sense that recursion can be simulated by means of process passing and communication. The CHOCS language is also studied by means of a denotational semantics. A major result is the full abstractness of this semantics with respect to the operational semantics. The denotational semantics is used to provide an easy proof of the simulation of recursion. Introducing processes as first class objects yields a powerful metalanguage. It is shown that it is possible to simulate various reduction strategies of the untyped λ-Calculus in CHOCS. As pointed out by Milner, CCS has its limitations when one wants to describe unboundedly expanding systems, e.g. an unbounded number of procedure invocations in an imperative concurrent programming language P with recursive procedures. CHOCS may neatly describe both call-by-value and call-by-reference parameter mechanisms for P. We also consider call-by-name and lazy parameter mechanisms for P. The second calculus is called Plain CHOCS. Essential to the new calculus is the treatment of restriction as a static binding operator on port names. This calculus is given an operational semantics using labelled transition systems which combines ideas from the applicative transition systems described by Abramsky and the transition systems used for CHOCS. This calculus enjoys algebraic properties which are similar to those of CHOCS only needing obvious extra laws for the static nature of the restriction operator. Processes as first class objects enable description of networks with changing interconnection structure and there is a close connection between the Plain CHOCS calculus and the π-Calculus described by Milner, Parrow and Walker: the two calculi can simulate one another. Recently object oriented programming has grown into a major discipline in computational practice as well as in computer science. From a theoretical point of view object oriented programming presents a challenge to any metalanguage since most object oriented languages have no formal semantics. We show how Plain CHOCS may be used to give a semantics to a prototype object oriented language called 0.Open Acess

    Process Algebras

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    Denotational Semantics of Mobility in Unifying Theories of Programming (UTP)

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    UTP promotes the unification of programming theories and has been used successfully for giving denotational semantics to Imperative Programming, CSP process algebra, and the Circus family of programming languages, amongst others. In this thesis, we present an extension of UTP-CSP (the UTP semantics for CSP) with the concept of mobility. Mobility is concerned with the movement of an entity from one location (the source) to another (the target). We deal with two forms of mobility: • Channel mobility, concerned with the movement of links between processes, models networks with a dynamic topology; and • Strong process mobility, which requires to suspend a running process first, and then move both its code and its state upon suspension, and finally resume the process on the target upon reception. Concerning channel mobility: • We model channels as concrete entities in CSP, and show that it does not affect the underlying CSP semantics. • A requirement is that a process may not own a channel prior to receiving it. In CSP, the set of channels owned by a process (called its interface) is static by definition. We argue that making the interface variable introduces a paradox. We resolve this by introducing a new concept: the capability of a process, and show how it relates to the interface. We then define channel mobility as the operation that changes the interface of a process, but not its capability. We also provide a functional link between static CSP and its mobile version. Concerning strong mobility, we provide: • The first extension of CSP with jump features, using the concept of continuations. • A novel semantics for the generic interrupt (a parallel-based interrupt operator), using the concept of Bulk Synchronous Parallelism. We then define strong mobility as a specific interrupt operator in which the interrupt routine migrates the suspended program

    Models for Concurrency

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    Revised version of DAIMI PB-429 This is, we believe, the final version of a chapter for the Handbook of Logic and the Foundations of Computer Science, vol. IV, Oxford University Press.It surveys a range of models for parallel computation to include interleaving models like transition systems, synchronisation trees and languages (often called Hoare traces in this context), and models like Petri nets, asynchronous transition systems, event structures, pomsets and Mazurkiewicz traces where concurrency is represented more explicitly by a form of causal independence.The presentation is unified by casting the models in a category-theoretic framework. One aim is to use category theory to provide abstract characterisations of constructions like parallel composition valid throughout a range of different models and to provide formal means for translating between different models. A knowledge of basic category theory is assumed, up to an acquaintance with the notion of adjunction

    Comparative Studies, Formal Semantics and PVS Encoding of CSP#

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