An ETL Process for OLAP Using RDF/OWL Ontologies

In this paper, we present an advanced method for on-demand construction of OLAP cubes for ROLAP systems. The method contains the steps from cube design to ETL but focuses on ETL. Actual data analysis can then be done using the tools and methods of the OLAP software at hand. The method is based on RDF/OWL ontologies and design tools. The ontology serves as a basis for designing and creating the OLAP schema, its corresponding database tables, and finally populating the database. Our starting point is heterogeneous and distributed data sources that are eventually used to populate the OLAP cubes. Mapping between the source data and its OLAP form is done by converting the data first to RDF using ontology maps. Then the data are extracted from its RDF form by queries that are generated using the ontology of the OLAP schema. Finally, the extracted data are stored in the database tables and analysed using an OLAP software. Algorithms and examples are provided for all these steps. In our tests, we have used an open source OLAP implementation and a database server. The performance of the system is found satisfactory when testing with a data source of 450 000 RDF statements. We also propose an ontology based tool that will work as a user interface to the system, from design to actual analysis.

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