The MammoGrid project has recently delivered its first proof-of-concept prototype using a Service-Oriented Architecture (SOA)-based Grid application to enable distributed computing spanning national borders. The underlying AliEn Grid infrastructure has been selected because of its practicality and because of its emergence as a potential open source standards-based solution for managing and coordinating distributed resources. The resultant prototype is expected to harness the use of huge amounts of medical image data to perform epidemiological studies, advanced image processing, radiographic education and ultimately, tele-diagnosis over communities of medical 'virtual organisations'. The Mam-moGrid prototype comprises a high-quality clinician visualization workstation used for data acquisition and inspection, a DICOM-compliant interface to a set of medical services (annotation, security, image analysis, data storage and querying services) residing on a socalled 'Grid-box' and secure access to a network of other Grid-boxes connected through Grid middleware. This paper outlines the MammoGrid approach in managing a federation of Grid-connected mammography databases in the context of the recently delivered prototype and will also describe the next phase of prototyping.
Abstract. One of the main factors driving object-oriented software development for information systems is the requirement for systems to be tolerant to change. To address this issue in designing systems, this paper proposes a pattern-based, object-oriented, description-driven system (DDS) architecture as an extension to the standard UML four-layer meta-model. A DDS architecture is proposed in which aspects of both static and dynamic systems behavior can be captured via descriptive models and meta-models. The proposed architecture embodies four main elementsfirstly, the adoption of a multi-layered meta-modeling architecture and reflective meta-level architecture, secondly the identification of four data modeling relationships that can be made explicit such that they can be modified dynamically, thirdly the identification of five design patterns which have emerged from practice and have proved essential in providing reusable building blocks for data management, and fourthly the encoding of the structural properties of the five design patterns by means of one fundamental pattern, the Graph pattern. A practical example of this philosophy, the CRISTAL project, is used to demonstrate the use of description-driven data objects to handle system evolution.Keywords: meta-models, system description, UML, design patterns, reflection IntroductionMany approaches have been proposed to address aspects of design and implementation for modern object-oriented systems. Each has its merits and focuses on concerns such as data , which have recognized and begun to address these failings. This paper advocates a design and implementation approach that is systemic (or holistic) in nature, viewing the development of modern object-oriented software from a systems standpoint. The philosophy that has been investigated is based on the systematic capture of the description of systems elements covering multiple views of the system to be designed (including data, process and time views) using familiar techniques. The approach advocated here has been termed description-driven and its underlying patterns are the subject of this paper. Essentially the description-driven approach involves identifying and abstracting the crucial elements (such as items, processes, lifecycles, goals, agents and outcomes) in the system under design and creating high-level descriptions of these elements which are stored, dynamically modified and managed separately from their instances.In the object oriented community well-known design patterns [5] have been named, described and cataloged for reuse by the community as a whole. This approach has enabled us to make use of design patterns that were proven on previous projects and is an example of reuse at the larger grain design level. Our studies have also benefited from the use of frameworks: reusable semicomplete applications that can be specialized to produce custom applications. Frameworks specify reusable architectures for all or part of a system and may include reusable classes, patterns or templates. We note that...
One of the main factors driving object-oriented software development in the Web-age is the need for systems to evolve as user requirements change. A crucial factor in the creation of adaptable systems dealing with changing requirements is the suitability of the underlying technology in allowing the evolution of the system. A reflective system utilizes an open architecture where implicit system aspects are reified to become explicit first-class (metadata) objects. These implicit system aspects are often fundamental structures which are inaccessible and immutable, and their reification as meta-data objects can serve as the basis for changes and extensions to the system, making it self-describing. To address the evolvability issue, this paper proposes a reflective architecture based on two orthogonal abstractions -model abstraction and in-formation abstraction. In this architecture the modeling abstractions allow for the separation of the description meta-data from the system aspects they represent so that they can be managed and versioned independently, asynchronously and explicitly. A practical example of this philosophy, the CRISTAL project, is used to demonstrate the use of meta-data objects to handle system evolution.
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