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netzspannung.org - system architecture and platform technology

A distributed Internet application system has been developed at netzspannung.org within the framework of the CAT project, for networking and bundling locally and organizationally distributed communities in the fields of art, culture and technology. The system has been specially designed for the adaptive formation of open communities, where the members not only use an already defined network of available resources, but also actively participate in the further shaping and development of the network. This involves integrating distributed components into a cross-platform application environment; networking heterogeneous resources; and supporting nomadic desktop applications.
› Scientific Papers about Platform Technology


Starting with a central Internet platform, i.e. netzspannung.org, a distributed Internet application system is built up. The focus is on integrating, networking, distributing and visualizing both content and applications, and on personalizing the respective application environment on the basis of user profiles. This can be seen in Fig. 1.
Fig. 1: Concept
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With this in mind, a cross-platform application system must provide interfaces for the dynamic expansion, with which new content can be integrated, and external services "docked" using web services. Alongside standard visualisation in a web browser, special interfaces are offered through web applications such as the Timeline or Semantic Map, which can be dynamically downloaded onto the local computer and executed.
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System architecture

netzspannung.org's application system is implemented in Java and based on an open system architecture which can be dynamically expanded with specific modules and components. During ongoing operation, new services and applications can be loaded into the system on request and then run. A special database interface (distributed storage system) ensures that heterogeneous data sources can be addressed in a uniform object-oriented manner, thus enabling applications to be developed independently, as outlined in Fig. 2.
Fig. 2: System architecture
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New data sources can be incorporated using specific plug-ins. On the other hand, netzspannung.org offers - via different communication interfaces (open network architecture) - a variety of accesses to its archives, applications and services. These interfaces include linking with external services via web services, or integrating client-side tools written in Flash or Java, such as the Timeline and Semantic Map. In addition, content in the form of dynamic web pages processed by Java servlets can be queried and displayed on conventional browsers. Multimedia content is transmitted onto the Internet with a streaming server. In this way, archived contributions, e.g. in tele-lectures, can be re-accessed at any time and events such as "Iconic Turn" can be followed in real time.
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Cross-platform application environment

An important objective of the technical development has been a cross-platform application environment for networking and integrating heterogeneous resources, such as application components, databases and external Internet portals, and search engines.
Fig. 3: Distributed application components
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To this end, users can add self-designed modules and databases to the community, which can then be either distributed in the network or made available on their own computers, as illustrated in Fig. 3. Developers deposit new application modules - together with a description - in module repositories. From there the modules can be dynamically downloaded onto a remote computer and assembled into an application. The application and platform descriptions are evaluated, and the corresponding execution environment is created on the destination computer. All applications and services at netzspannung.org, such as the workspace, netzkollektor, the search facility and the digital sparks conference system, are loaded and composed from individual modules in this way. In the process, the statuses of different versions - as well as various dependencies - are examined and automatically resolved by the central application environment. It is only this "de-composition" of the system that allows the parallel and distributed development of netzspannung.org with diverse partners, such as Siegen University.
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Networking of heterogeneous resources and applications

A further stage of development will enable networking with existing resources, such as search engines, which cannot be directly linked into the application environment. Existing technologies from the area of web services will be used for this service-oriented integration of existing applications, external search engines and Internet portals, as well as for the publication of members' own content and services, as illustrated in Fig. 4.
Fig. 4: Networking of external ressources with web services
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The networking takes place through specific web service adapters, which must be provided for each particular resource and integrated into netzspannung.org as a plug-in. In this way heterogeneous resources are also accessible via a homogeneous interface and can be further used in custom services, such as the cross-platform search, semantic text analysis and networked archives. An example of this networking is the integration into netzspannung.org of the AWAKE knowledge management system. First the content of netzspannung.org is made available via web services for semantic evaluation and processing in knowledge maps, and then these results flow back again via web services to netzspannung.org, where they are visualized with the Semantic Map.
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Nomadic desktop computing

As a distributed Internet application system, netzspannung.org is not only designed for web-based use with a browser, but also offers other forms of interactivity, which can be made available on the user's desktop computer through downloaded applications and tools. The objective is to create a cross-platform application environment of a kind that is particularly beneficial to so called "nomadic" users. In the nomadic desktop computing scenario, a user makes use of different stationary desktop systems, as shown in Fig. 5.
Fig. 5: Nomadic desktop computing
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The user receives a migrating application environment, which makes his applications available in the same configuration on every linked desktop system. netzspannung.org's underlying architecture and implementation provide the basis for the next development stage, which, will enable this distribution of services and applications. Here special attention will be given to advancing personalization, which is intended to cover the expanded configuration and interaction possibilities
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The distributed netzspannung.org Internet platform is not based on a fixed implementation, but grows with the conceptual and content-oriented requirements arising from changing application scenarios. Starting from its role as a content provider for communicating culture (with the focus on creating a web portal), the platform has developed into a service provider on the basis of web services, used for particular purposes such as knowledge discovery or e-learning applications. In future application scenarios, increasing importance will be attached to providing new tools by means of nomadic web applications and support for nomadic desktop systems. The system architecture presented here, as well as the technologies that have been developed, will ensure that netzspannung.org grows with requirements, and that users continue to have an opportunity to help shape the platform.

Scientific Papers about Platform Technology

PAAL, Stefan; KAMMÜLLER, Reiner; FREISLEBEN, Bernd: Adaptable Web Interfaces for Heterogeneous Data Sources. In: Proceedings of the 2nd Conference on Internet Computing (IC 2001). Las Vegas, USA. CSREA 2001. pp. 827-834.
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PAAL, Stefan; KAMMÜLLER, Reiner; FREISLEBEN, Bernd: Customizable Deployment, Composition and Hosting of Distributed Java Applications. Distributed Objects and Applications (DOA 2002). LNCS 2519. Irvine, USA: Springer, 2002, pp. 845-865.
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PAAL, Stefan; KAMMÜLLER, Reiner; FREISLEBEN, Bernd: Java Remote Object Binding with Method Streaming. Proceedings of the 4th International Conference for Objects, Components, Architectures, Services and Applications for a Networked World (NODE 2003). Erfurt, Germany. 2003, pp. 230-244.
› Download [PDF | 300 KB]

PAAL, Stefan; KAMMÜLLER, Reiner; FREISLEBEN, Bernd: Separating the Concerns of Distributed Deployment and Dynamic Composition in Internet Application Systems. Distributed Objects and Applications (DOA 2003). LNCS 2888. Catania, Italy: Springer, 2003, pp. 1292-1311.
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PAAL, Stefan; KAMMÜLLER, Reiner; FREISLEBEN, Bernd: A Cross-Platform Application Environment for Nomadic Desktop Computing. Proceedings of the 5th International Conference for Objects, Components, Architectures, Services and Applications for a Networked World (NODE 2004). Erfurt, Germany. 2004. (to be published).

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