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Abstract. In this paper we present lessons learned from building a Semantic Desktop system, the gnowsis beta. On desktop computers, semantic software has to provide stable services and has to reflect the personal view of the user. Our approach to ontologies, the Personal Information Model PIMO allows to create tagging services like del.icio.us on the desktop. A semantic wiki allows further annotations. Continuous evaluations of the system helped to improve it. These results were created in the EPOS research project and are available in the open source projects Aperture, kaukoluwiki, and gnowsis and will be continued in the Nepomuk project. By using these components, other developers can create new desktop applications the web 2.0 way.

Abstract. Many approaches for RDF stores exist, most of them using very straight-forward techniques to store triples in or mapping RDF Schema classes to database tables. In this paper we propose an RDF store that uses a natural mapping of RDF resources to database tables that does not rely on RDF Schema, but constructs a schema based on the occurring signatures, where a signature is the set of properties used on a resource. This technique can therefore be used for arbitrary RDF data, i.e., RDF Schema or any other schema/ontology language on top of RDF is not required. Our approach can be used for both in-memory and on-disk relational database-based RDF store implementations.A first prototype has been implemented and already shows a significant performance increase compared to other freely available (inmemory) RDF stores.

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