The Grid-enabled Semantic Data Access Middleware (G-SDAM) is designed as an OGSA-compliant Grid middleware enabling virtual integration of distributed and heterogenous data sources in a Grid environment by applying Semantic Web technologies. The core of the middleware is the Semantic Web Integrator and Query Processor (SemWIQ), being developed to enable distributed SPARQL query processing.
Introduction
For scientific collaboration, sharing data between different parties is fundamental. Grids, originally developed for high-performance and parallel computing, enable the sharing of distributed resources across institutional boundaries by providing a security infrastructure and standardized Grid-services. Because data is usually stored in different information systems and schemes, at the moment they have to be prepared and manually aligned to a common schema. Knowledge about data structures and semantics is a precondition to be able to integrate data sources. To enable virtual integration, several concepts have been proposed in the field of distributed and federated database systems. For the integration of heterogeneous information systems, the mediator-wrapper architecture can be used. In order to fulfill the requirements of a Grid-based data integration middleware for distributed, heterogeneous data sources, several concepts introduced in the Semantic Web community have been considered. The Resource Description Framework (RDF) is well suited for global schema management. It is simple, supports modularization of commonly used semantics by the ontology layer, and allows for reasoning. A standardized query language (SPARQL) is currently being developed by the community. Although SPARQL also provides a client/server protocol, currently queries are targeted to single sites only. For large-scale data integration it is necessary to distribute and optimize query plans accross multiple data nodes.
The figure on the right shows the prototype scenario for integration of solar observation data. Solid lines show links between Grid nodes, dot-dashed lines show links from the global repository node to local data nodes. A scientist sitting on a workstation which is part of the Grid (on the bottom) can execute a query referring to globally defined concepts and retrieve available observation data stored on different sites in different information systems.
Acknowledgements
This work is funded by the Austrian BMBWK (Federal Ministry for Education, Science and Culture), contract GZ BMWF-10.220/0002-II/10/2007.
License
Unless otherwise noted, the following copyright statement applies:
© Copyright 2006 Institute for Applied Knowledge Processing, Johannes Kepler University Linz, Austria, http://www.faw.uni-linz.ac.at
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
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