The semantic web represents meta-data as a triple relation using the RDF data model. We have developed a system to process queries to RDF views of entire relational databases. Optimization of queries to such views is challenging because i) RDF views of entire relational databases become large unions, and ii) queries to the views are more general than relational database queries, making no clear distinction between data and schema. As queries need not be expressed in terms of a schema, it becomes critical to optimize not only data access time but also the time to perform the query optimization itself. We have developed novel query optimization techniques for scalable queries to RDF views of relational databases. Our optimization techniques are based on partial evaluation, a method for compile time evaluation of subexpressions. We show dramatic improvements in query optimization time when scaling the query size while still producing high quality execution plans. Our query optimization techniques enable execution of real-world queries to RDF views of relational databases.
Note: Updated April 2006
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