8 research outputs found

    TUPLESPACE-BASED INFRASTRUCTURE FOR DECENTRALIZED ENACTMENT OF BPEL PROCESSES

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    Business processes in WS-BPEL are a manifestation of the two-level-programming paradigm where remote-accessible Web services are composed to potentially complex orchestrations. WSBPEL processes are executed by Workflow Management Systems that navigate through the process\u27 activities and interact with the orchestrated services. While Web service technology enables interactions with remote services, process navigation is typically done in a centralized manner. Especially in scenarios of complex interactions between multiple distributed process participants, this way of process enactment has several drawbacks. In this paper, we outline those drawbacks and propose an alternative approach to execution of BPEL processes in a distributed, decentralized manner

    CSP as a Coordination Language. A CSP-based Approach to the Coordination of Concurrent Systems

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    Die Beherrschbarkeit komplexer nebenläufiger Systeme hängt in hohem Maße davon ab, mit welchen Methoden das System modelliert bzw. spezifiziert wird. Formale auf Nebenläufigkeit spezialisierte Methoden erlauben es, solche Systeme elegant auf einem hohen Abstraktionsniveau zu modellieren und zu analysieren. Ein Vertreter derartiger Methoden ist die in dieser Arbeit verwendete Prozess Algebra CSP. CSP ist ein weitverbreiteter, wohluntersuchter Formalismus, der es erlaubt, ein nebenläufiges System mathematisch präzise zu beschreiben und wichtige Eigenschaften, beispielsweise Verklemmungsfreiheit, zu verifizieren. Dennoch ist die Ableitung einer Systemimplementierung aus einem gegebenen CSP Modell immer noch ein aktueller Forschungsgegenstand. So ist zum Beispiel unklar, wie interne Aktionen eines Systems in einer Implementierung integriert werden können, da diese in CSP ununterscheidbar sind. Als Lösung wird in dieser Arbeit vorgeschlagen, CSP mit einer sequentiellen Zielsprache zu integrieren, so dass die Aktionen eines Systems in der sequentiellen Zielsprache implementiert werden und die Aktionen entsprechend eines CSP Prozesses koordiniert werden. Koordinationssprachen zielen ebenfalls darauf ab, Nebenläufigkeit von sequentiellen Aspekten eines Systems zu trennen, sie sind aber weniger auf automatisierte formale Verifikation ausgerichtet. In der Arbeit wird die Verwendung der Prozess Algebra CSP als formale Koordinationssprache für beliebige sequentielle Zielsprachen vorgeschlagen. Hierfür wird das formale Fundament einer Koordinationsumgebung entwickelt, die einen CSP Prozess zur Laufzeit simuliert und die Aktionen des Systems entsprechend ausführt. Besonderer Wert liegt auf der Koordination interner Aktionen und auf der Erkennung von Nebenläufigkeit zwischen extern synchronisierbaren und internen Aktionen. Durch Beweisverpflichtungen wird der Zusammenhang zwischen dem Koordinationsprozess und den Implementierungen der Aktionen hergestellt. Die Koordinationsumgebung wird konkret für die Zielsprache Java implementiert. Desweiteren wird eine Fallstudie vorgestellt, die sich mit der Entwicklung eines Workflow Servers beschäftigt, dessen interne Nebenläufigkeit einerseits selbst mittels CSP koordiniert wird und der andererseits CSP-basierte Workflows ausführen kann, die ebenfalls durch eine CSP Koordinationsumgebung gesteuert werden. Die Arbeit enthält wissenschaftliche Beiträge zur Theorie und der praktischen Verwendbarkeit von CSP, bezüglich der Konstruktion korrekter nebenläufiger Systeme, sowie zum Bereich der Modellierung und Verwaltung von Workflows.Complex concurrent systems are in general hard to understand, and equally hard to specify and to verify. The process algebra Communicating Sequential Processes (CSP) offers a way of taming the complexity of concurrent systems by focusing on the interaction behavior of systems and abstracting from synchronization mechanisms and other implementation details. CSP provides a mature intermediate level formalism that allows us to specify and model such systems in a mathematically precise way and to verify important properties, e. g., deadlock-freedom. However, the derivation of a system’s implementation from its CSP-based model is still a problem and sub ject to ongoing research. It is, for example, not obvious how to integrate CSP with internal actions of a system, because CSP abstracts from internal actions to a great extent. To overcome this problem, we propose to integrate CSP with a sequential host language such that the concurrency aspects of systems are captured on the CSP level and its actions are implemented in the sequential host language. This idea of separating concurrent and sequential aspects of a system is also known from coordination languages, but those are in general less amenable to automated verification. In this thesis, we present the use of CSP as a formal coordination language for arbitrary sequential host languages, allowing us to use CSP for the design, implementation, and verification of concurrent systems. To this end, we develop the model of a coordination environment that simulates a CSP process at runtime and performs the system’s actions accordingly. The coordination environment controls the system’s interaction with its environment as well as its internal actions. We present proof obligations to ensure that the properties proved on the CSP level also hold on the implementation level of the system. We also present an implementation of the coordination environment for the target language Java and a case study of constructing a workflow server as a coordinated concurrent Java program. This thesis contributes to the theory and practice of CSP, to the engineering of correct concurrent systems, and to the modeling and management of workflows. The main contribution of this thesis is a target language independent CSP-based framework for the construction of provably correct concurrent systems

    End-User Service Computing: Spreadsheets as a Service Composition Tool

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    In this paper, we show how spreadsheets, an end-user development paradigm proven to be highly productive and simple to learn and use, can be used for complex service compositions. We identify the requirements for spreadsheet-based service composition, and present our framework that implements these requirements. Our framework enables spreadsheets to send requests and retrieve results from various local and remote services. We show how our tools support different composition patterns, and how the style of declarative dependencies of spreadsheets can facilitate service composition. We also discuss novel issues identified by using the framework in several projects and education

    A Model for Scientific Workflows with Parallel and Distributed Computing

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    In the last decade we witnessed an immense evolution of the computing infrastructures in terms of processing, storage and communication. On one hand, developments in hardware architectures have made it possible to run multiple virtual machines on a single physical machine. On the other hand, the increase of the available network communication bandwidth has enabled the widespread use of distributed computing infrastructures, for example based on clusters, grids and clouds. The above factors enabled different scientific communities to aim for the development and implementation of complex scientific applications possibly involving large amounts of data. However, due to their structural complexity, these applications require decomposition models to allow multiple tasks running in parallel and distributed environments. The scientific workflow concept arises naturally as a way to model applications composed of multiple activities. In fact, in the past decades many initiatives have been undertaken to model application development using the workflow paradigm, both in the business and in scientific domains. However, despite such intensive efforts, current scientific workflow systems and tools still have limitations, which pose difficulties to the development of emerging large-scale, distributed and dynamic applications. This dissertation proposes the AWARD model for scientific workflows with parallel and distributed computing. AWARD is an acronym for Autonomic Workflow Activities Reconfigurable and Dynamic. The AWARD model has the following main characteristics. It is based on a decentralized execution control model where multiple autonomic workflow activities interact by exchanging tokens through input and output ports. The activities can be executed separately in diverse computing environments, such as in a single computer or on multiple virtual machines running on distributed infrastructures, such as clusters and clouds. It provides basic workflow patterns for parallel and distributed application decomposition and other useful patterns supporting feedback loops and load balancing. The model is suitable to express applications based on a finite or infinite number of iterations, thus allowing to model long-running workflows, which are typical in scientific experimention. A distintive contribution of the AWARD model is the support for dynamic reconfiguration of long-running workflows. A dynamic reconfiguration allows to modify the structure of the workflow, for example, to introduce new activities, modify the connections between activity input and output ports. The activity behavior can also be modified, for example, by dynamically replacing the activity algorithm. In addition to the proposal of a new workflow model, this dissertation presents the implementation of a fully functional software architecture that supports the AWARD model. The implemented prototype was used to validate and refine the model across multiple workflow scenarios whose usefulness has been demonstrated in practice clearly, through experimental results, demonstrating the advantages of the major characteristics and contributions of the AWARD model. The implemented prototype was also used to develop application cases, such as a workflow to support the implementation of the MapReduce model and a workflow to support a text mining application developed by an external user. The extensive experimental work confirmed the adequacy of the AWARD model and its implementation for developing applications that exploit parallelism and distribution using the scientific workflows paradigm

    The Paragraph: Design and Implementation of the STAPL Parallel Task Graph

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    Parallel programming is becoming mainstream due to the increased availability of multiprocessor and multicore architectures and the need to solve larger and more complex problems. Languages and tools available for the development of parallel applications are often difficult to learn and use. The Standard Template Adaptive Parallel Library (STAPL) is being developed to help programmers address these difficulties. STAPL is a parallel C++ library with functionality similar to STL, the ISO adopted C++ Standard Template Library. STAPL provides a collection of parallel pContainers for data storage and pViews that provide uniform data access operations by abstracting away the details of the pContainer data distribution. Generic pAlgorithms are written in terms of PARAGRAPHs, high level task graphs expressed as a composition of common parallel patterns. These task graphs define a set of operations on pViews as well as any ordering (i.e., dependences) on these operations that must be enforced by STAPL for a valid execution. The subject of this dissertation is the PARAGRAPH Executor, a framework that manages the runtime instantiation and execution of STAPL PARAGRAPHS. We address several challenges present when using a task graph program representation and discuss a novel approach to dependence specification which allows task graph creation and execution to proceed concurrently. This overlapping increases scalability and reduces the resources required by the PARAGRAPH Executor. We also describe the interface for task specification as well as optimizations that address issues such as data locality. We evaluate the performance of the PARAGRAPH Executor on several parallel machines including massively parallel Cray XT4 and Cray XE6 systems and an IBM Power5 cluster. Using tests including generic parallel algorithms, kernels from the NAS NPB suite, and a nuclear particle transport application written in STAPL, we demonstrate that the PARAGRAPH Executor enables STAPL to exhibit good scalability on more than 10410^4 processors

    Supporting Collaboration in Mobile Environments

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    Continued rapid improvements in the hardware capabilities of mobile computing devices is driving a parallel need for a paradigm shift in software design for such devices with the aim of ushering in new classes of software applications for devices of the future. One such class of software application is collaborative applications that seem to reduce the burden and overhead of collaborations on human users by providing automated computational support for the more mundane and mechanical aspects of a cooperative effort. This dissertation addresses the research and software engineering questions associated with building a workflow-based collaboration system that can operate across mobile ad hoc networks, the most dynamic type of mobile networks that can function without dependence on any fixed external resources. While workflow management systems have been implemented for stable wired networks, the transition to a mobile network required the development of a knowledge management system for improving the predictability of the network topology, a mobility-aware specification language to specify workflows, and its accompanying algorithms that help automate key pieces of the software. In addition to details of the formulation, design, and implementation of the various algorithms and software components. this dissertation also describes the construction of a custom mobile workflow simulator that can be used to conduct simulation experiments that verify the effectiveness of the approaches presented in this document and beyond. Also presented are empirical results obtained using this simulator that show the effectiveness of the described approaches
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