Topology, randomness and noise in process calculus

We introduce the first process algebra with non-blocking reading actions for modelling concurrent asynchronous systems. We study the impact this new kind of actions has on fairness, liveness and the timing of systems, using as application Dekker’s mutual exclusion algorithm we already considered in [4]. Regarding some actions as reading, this algorithm satisfies MUTEX liveness already under the assumption of fairness of actions. We demonstrate an interesting correspondence between liveness and the catastrophic cycles that we introduced in [6] when studying the performance of pipelining. Finally, our previous result on the correspondence between timing and fairness [4] scales up to the extended language.

Process algebra provides abstract and rigorous means for studying communicating concurrent systems. Coordination languages also provide abstract means for the specifying and programming communication of components. Hence, the two fields seem to have very much in common and the link between these two research areas have been established formally by means of several translations, mainly from coordination languages to process algebras. There have also been proposals of process algebras whose communication policy is inspired by the one underlying coordination languages. The aim of this workshop was to push the state of the art in the study of the connections between process algebra and coordination languages by bringing together experts as well as young researchers from the two fields to communicate their ideas and findings. It includes both contributed and invited papers that have been presented during the one day meeting on Process Algebra and Coordination (PACO 2011) which took place on June 9, 2011 in Reykjavik, Iceland.

In this paper we present a process algebra approach for the integrated verification of correctness and performance in concurrent systems. The verification procedure is entirely performed within the Circal process algebra, without any recourse to other formalisms. Performance is characterised in terms of logical properties, which do not incorporate explicit time. Such properties are then interpreted in terms of degree of parallelism and allow the quantitative evaluation of the throughput of the system. The approach has been applied to two four-phase handshaking protocols, which are motivated by the implementation of the AMULET2 asynchronous RISC processor. Both correctness and performance properties are captured in the same verification framework and automatically proved using the Circal System.

Reversible debuggers help programmers to find the causes of misbehaviours in concurrent programs more quickly, by executing a program backwards from the point where a misbehaviour was observed, and looking for the bug(s) that caused it. Reversible debuggers can be founded on the well-studied theory of causal-consistent reversibility, which only allows one to undo an action provided that its consequences, if any, are undone beforehand. Causal-consistent reversibility yields more efficient debugging by reducing the number of states to be explored when looking backwards. Till now, causal-consistent reversibility has never considered time, which is a key aspect in real-world applications. Here, we study the interplay between reversibility and time in concurrent systems via a process algebra. The Temporal Process Language (TPL) by Hennessy and Regan is a well-understood extension of CCS with discrete-time and a timeout operator. We define revTPL, a reversible extension of TPL, and we show that it satisfies the properties expected from a causal-consistent reversible calculus. We show that, alternatively, revTPL can be interpreted as an extension of reversible CCS with time.

Modern day computer architectures offer ever-increasing support for parallel processing, still it turns out to be quite difficult for programmers and therefore programs to tap into these parallel resources. To benefit from real general-purpose parallel computing we claim that it is likely that a paradigm shift is needed in the way we think about programming. This change of thought in turn will need to be reflected in future programming languages as well. We think that the field of process algebra provides thorough insight in how to reason about the construction of software for concurrent systems and will be one of the enabling technologies supporting this transition. The wish to connect process algebra, a mathematical theory, to the world of computer-readable and executable specifications led to the development of PSF (Process Specification Formalism). PSF is an implementation of the process algebra ACP (Algebra of Communicating Processes) integrating ASF (Algebraic Specification Formalism) to specify algebraic data types. One of the first publications on PSF appeared in Fundamenta Informaticae in 1990. Here we stated as the first sentence of the abstract: "Traditional methods for programming sequential machines are inadequate for specifying parallel systems". Unfortunately, though some advancements have been made since 1990, we can still uphold this statement 20 years later. This current report documents the developments that lead to the construction of PSF and the 1990 publication and moreover it also documents how PSF and its tools have evolved since 1990 taking the conclusion and the outlook for future work from the original article as a reference point. Using the knowledge gained both in constructing tools for PSF and in using PSF to specify concurrent systems, we will judge, discuss and criticise the design decisions taken and show paths for future developments.

Process algebra provides essential tools for studying concurrent systems. An important branch of process algebra is value passing CCS. However, value passing CCS lacks not only action refinement, which is an essential operation in the design of concurrent systems, but also non-interleaving semantics, which is appropriate to specify the partial order and equivalence relations. In this paper, we will define action refinement and non-interleaving semantics by valued stable event structures and valued labeled configuration structures in which special valued actions will be executed. The refinement operation and semantics are useful for the hierarchical design methodology in value passing CCS, e.g. top-down system design.

Formal method is an effective way for modeling and verifying concurrent system. An important research field is to describe and verify Web services by formal method. Guaranteeing the validity of Web services composition is necessary for enhancing the value of this composite service. CCS is a kind of process algebra which can be used to model concurrent systems. Web services and their composition are described and modeled based on CCS in this paper. Rules about applying CCS to Web services are explained. Finally, a case study is carried and the validity of composition model is verified. Some important points in verification are discussed

Quantum cryptographic systems have been commercially available, with a striking advantage over classical systems that their security and ability to detect the presence of eavesdropping are provable based on the principles of quantum mechanics. On the other hand, quantum protocol designers may commit much more faults than classical protocol designers since human intuition is much better adapted to the classical world than the quantum world. To offer formal techniques for modeling and verification of quantum protocols, several quantum extensions of process algebra have been proposed. One of the most serious issues in quantum process algebra is to discover a quantum generalization of the notion of bisimulation, which lies in a central position in process algebra, preserved by parallel composition in the presence of quantum entanglement, which has no counterpart in classical computation. Quite a few versions of bisimulation have been defined for quantum processes in the literature, but in the best case they are only proved to be preserved by parallel composition of purely quantum processes where no classical communications are involved. Many quantum cryptographic protocols, however, employ the LOCC (Local Operations and Classical Communications) scheme, where classical communications must be explicitly specified. So, a notion of bisimulation preserved by parallel composition in the circumstance of both classical and quantum communications is crucial for process algebra approach to verification of quantum cryptographic protocols. In this paper we introduce a novel notion of bisimulation for quantum processes and prove that it is congruent with respect to various process algebra combinators including parallel composition even when both classical and quantum communications are present. We also establish some basic algebraic laws for this bisimulation. In particular, we prove uniqueness of the solutions to recursive equations of quantum processes, which provides a powerful proof technique for verifying complex quantum protocols.

With the rapid evolution of mobile communication technology, the short message service (SMS) is the most important and essential operating business. The Pi calculus is a process algebra that describes the concurrent, dynamic and mobile systems. This paper depicts the behaviors of SMS service based on Pi calculus, including the formal description of fixed and mobile area. The formal model for SMS service is introduced and the storage-transmit mechanisms are discussed. The mobility features are represented with Pi calculus that the mobile process is controlled by switching the channel and the moving user still accurately receives any message. The formalizations can be used as a basis for future research on other mobile computing or wireless communication.

We present a comprehensive language theoretic causality analysis framework for explaining safety property violations in the setting of concurrent reactive systems. Our framework allows us to uniformly express a number of causality notions studied in the areas of artificial intelligence and formal methods, as well as define new ones that are of potential interest in these areas. Furthermore, our formalization provides means for reasoning about the relationships between individual notions which have mostly been considered independently in prior work; and allows us to judge the appropriateness of the different definitions for various applications in system design. In particular, we consider causality analysis notions for debugging, error resilience, and liability resolution in concurrent reactive systems. Finally, we present automata-based algorithms for computing various causal sets based on our language-theoretic encoding, and derive the algorithmic complexities.

In this chapter we introduce process algebras, a class of formal modelling techniques developed in theoretical computer science, and discuss their use within systems biology. These formalisms have a number of attractive features which make them ideal candidates to be intermediate, formal, compositional representations of biological systems. As we will show, when modelling is carried out at a suitable level of abstraction, the constructed model can be amenable to analysis using a variety of different approaches, encompassing both individuals-based stochastic simulation and population-based ordinary differential equations. We focus particularly on Bio-PEPA, a recently defined extension of the PEPA stochastic process algebra, which has features to capture both stoichiometry and general kinetic laws. We present the definition of the language, some equivalence relations and the mappings to underlying mathematical models for analysis. We demonstrate the use of Bio-PEPA on two biological examples.KeywordsStochastic SimulationProcess AlgebraContinuous Time Markov ChainBiochemical NetworkCommunicate Sequential ProcessThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Studying industrial systems by simulation enables the designer to study the dynamic behaviour and to determine some characteristics of the system. Unfortunately simulation also has some disadvantages. These can be overcome by using formal methods. Formal methods allow a thorough analysis of the possible behaviours of a system, parameterised system analysis and a modular approach to the analysis of systems. We present a case study in which a model of an industrial system is studied in a formal way. For this purpose, the model is first specified and simulated using the CSP-based executable specification language /spl chi/. The model is translated into a model in the process algebra ACP/sup T/. This enables us to give a correctness proof of the parameterised model and to study the model in isolation.

With the progress of low-power research on real-time systems, the estimation and analysis of energy consumption of real-time systems becomes a hot topic. Process Algebra is a formal method fit for analyzing the functional properties of real-time systems, but it can not analyze the energy consumption properties. This paper proposes a formal method support for modeling and analyzing energy consumption of real-time software. Resource Timed Communicating Sequential Process (RTCSP) is proposed in this paper can handle it efficiently by extending resource information on Timed Communicating Sequential Process (TCSP). In this paper, the power consumption of instructions in real-time systems is mapped into the resource of RTCSP, the energy consumption of real-time software can be modeled and optimized by using RTCSP, the optimal path algorithm is proposed to calculate the minimum energy consumption reachability path of real-time systems. This formal method improves the accuracy and efficiency of energy calculation, the calculation results can be used to quantitatively analyze and optimize the energy consumption of real-time systems.

Ojeblik is a lexically-scoped, object-based calculus that represents a distribution-free subset of the LAN-based programming language Obliq. The surrogate operation on Ojeblik-objects, which is the abstraction of migration on Obliq-objects, is a combined operation derived from the more primitive operations cloning and aliasing. In short, surrogation on an object turns the object into an alias for a clone of itself; it amounts to migration when the original and the clone reside on different distribution sites.In previous work, we studied the conditions under which surrogation is safe, i.e., transparent to object clients. To this aim, we developed two complementary formal descriptions of Ojeblik's semantics, one as an operational semantics on Ojeblik-configurations, and another one by translation into a process calculus. We used the former to explain typical (mis-)behaviors of Ojeblik programs, but only the latter to perform rigorous correctness proofs w.r.t. may-equivalence.In this paper, we offer new formal proofs, now based on the operational semantics of Ojeblik, making the results as well as the proofs accessible also to readers not familiar with process calculi. Furthermore, we strengthen our former results by using, in addition to may-equivalence, the much more distinguishing notion of must-equivalence.

Mathematical modelling and simulation modelling are fundamental tools of engineering, science, and social sciences such as economics, and provide decision-support tools in management. Mathematical models are essentially deployed at all scales, all levels of complexity, and all levels of abstraction. Models are often required to be executable, as a simulation, on a computer. We present some contributions to the process-theoretic and logical foundations of discrete-event modelling with resources and processes. Building on previous work in resource semantics, process calculus, and modal logic, we describe a process calculus with an explicit representation of resources in which processes and resources co-evolve. The calculus is closely connected to a substructural modal logic that may be used as a specification language for properties of models. In contrast to earlier work, we formulate the resource semantics, and its relationship with process calculus, in such a way that we obtain soundness and completeness of bisimulation with respect to logical equivalence for the naturally full range of logical connectives and modalities. We give a range of examples of the use of the process combinators and logical structure to describe system structure and behaviour.