Affiliations: Institute of Computer Science, Silesian University of Technology, Akademicka 16 street, 44-100 Gliwice, Poland. Tel.: +48 32 237 13 39; Fax: +48 32 237 27 33; E-mail: Marcin.Gorawski@polsl.pl, Rafal.Malczok@polsl.pl | [x] Faculdade de Economia, University of Porto, Rua Dr. Roberto Frias, 4200-464 Porto, Portugal. E-mail: mpbrito@fep.up.pt | [y] Institut d'Informatique, Facultés Universitaires Notre Dame de la Paix, Rue Grandgagnage, 21, B-5000 Namur, Belgium. E-mail: monique.noirhomme@info.fundp.ac.be
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Abstract: In this paper we present a Spatial Data Warehouse system that we use for aggregation and analysis of huge amounts of spatial data. The data is generated by utilities meters communicating via radio. In order to provide sufficient efficiency for our system we propose data and workload distribution as well as advanced indexing techniques. The system is based on a cascaded star model, which is a spatial development of a standard star schema and contains interconnected and often nested star schemas. The cascaded star allows efficient storage and analysis of spatial data, whose range extends from meter measurement values to weather information. The indexing tree structure and operation is tightly integrated with the spatial character of the data. Thanks to an available memory evaluating mechanism the system is very flexible in the field of aggregates accuracy. We also implemented indexing structure updating mechanism. The system is written in Java; for the data base we use Oracle 9i. Basing on the wide variety of tests results, we prove that a distributed system significantly surpasses the centralized version in terms of efficiency. We also show that a selective materialization of indexing structure fragments strongly increases system efficiency.
