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  • Radu Litiu, "Providing Flexibility in Distributed Applications Using a Mobile Component Framework", Ph.D. dissertation, University of Michigan, Electrical Engineering and Computer Science, Sep. 2000 (postscript - 1.1 MB ; pdf - 1.8 MB). (abstract)
    Abstract:
    Future distributed applications will need to support computing devices with a wide range of capabilities, varying network connectivity, increasing mobility of users, and a wide variation in load placed by clients on services. This dissertation addresses these challenges through the realization of a component-based framework, named DACIA, for building and executing adaptive distributed applications. Applications are viewed as graphs of connected components that typically implement data streaming, processing, and filtering functions. DACIA provides mechanisms for run-time reconfiguration of applications to allow them to adapt to the changing operating environments. Applications can dynamically load new components, change the way various components interact and exchange data, move components from one host to another, and replicate some components across multiple hosts.

    We identify the issues involved in runtime application reconfiguration. We propose an algorithm for performing dynamic reconfiguration while preserving the consistency and correctness of the application and minimizing the application disturbance. This algorithm executes in linear time with respect to the size of the application graph, and graciously handles failures that occur during the reconfiguration.

    Component mobility in DACIA provides support for mobile users and mobile applications. Logical connections between moving components are persistent. Messages are reliably and orderly delivered during and after component relocation. The execution of components connected to the moving component is not affected. Users do not see any interruptions in the services accessed, and they do not need to manually re-establish connections with the communication parties.

    We give several examples of applications implemented using DACIA, that demonstrate the benefits of using our framework, both from the performance and from the usability standpoint. DACIA is designed so that communication overheads are low, comparable to those of procedure calls when components are co-located and those of raw network communication when they are located on remote hosts. Moreover, the cost of moving components across hosts can be kept low. We show that by using simple adaptive heuristics to reconfigure an application, the performance of the application can be significantly improved compared to the static case in which the application structure is fixed.

  • Radu Litiu, and Atul Prakash, "Developing Adaptive Groupware Applications Using a Mobile Component Framework", Proceedings of the ACM 2000 Conference on Computer Supported Cooperative Work (CSCW 2000), Philadelphia, PA, December 2000.
    Abstract:
    There is a need to develop groupware systems that adapt to available resources and support user mobility. This paper presents DACIA (Dynamic Adjustment of Component InterActions), a system that provides mechanisms for building such groupware applications. Using DACIA, components of a groupware application can be moved to different hosts during execution, while maintaining communication connectivity with groupware services and other users. DACIA provides mechanisms that simplify building groupware for domains where users are mobile. New collaboration features can be also more easily implemented. For example, users may ``park'' their client agents temporarily at a fixed host while they are disconnected; the parked agent can continue to maintain connectivity with other group members on behalf of the user, if desired. DACIA is also applicable to non-mobile environments. We show its applicability to building groupware applications that can be reconfigured at run-time to adapt to changing user demands and resource constraints, for example, by relocating services or introducing new services. This paper describes the architecture of DACIA and its use in building adaptable groupware systems.
  • Radu Litiu, and Atul Prakash, "Challenges in Using a Mobile Component Framework to Develop Adaptive Groupware Applications", Proceedings of CBG 2000, the CSCW 2000 Workshop on Component-based Groupware, Philadelphia, PA, December 2000.
  • Radu Litiu, and Atul Prakash, "DACIA: A Mobile Component Framework for Building Adaptive Distributed Applications", Principles of Distributed Computing (PODC) 2000 Middleware Symposium, Portland, OR, July 2000; also appeared as Technical Report CSE-TR-416-99, Department of EECS, University of Michigan, Dec 1999.
    Abstract:
    Future distributed applications will need to support computing devices with a wide range of capabilities, varying network connectivity, increasing mobility of users, and a wide variation in load placed by clients on services. This paper presents DACIA (Dynamic Adjustment of Component InterActions), a framework for building adaptive distributed applications. In DACIA, distributed applications are viewed as consisting of connected components that typically implement data streaming, processing, and filtering functions. DACIA provides mechanisms for run-time reconfiguration of applications to allow them to adapt to the changing operating environments. Components can be moved to different hosts during execution, while maintaining communication connectivity with other components. New components can also be introduced along data paths, for example, to provide compression on low-bandwidth connections. Keeping communication overheads low is a significant challenge in designing component-based services. DACIA is designed so that communication costs among co-located components are similar to those of procedure calls. Performance results, as well as examples of adaptive services that can be built using DACIA are presented.

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