Abstract
Abstract: OLAP queries involve a lot of aggregations on a large amount of data in data warehouses. To process expensive OLAP queries efficiently, we propose a new method for rewriting a given OLAP query using various kinds of materialized aggregate views which already exist in data ware-houses. We first define the normal forms of OLAP queries and materialized views based on the lattice of dimension hierarchies, the semantic information in data warehouses. Conditions for usability of a materialized view in rewriting a given query are specified by relationships between the components of their normal forms. We present a rewriting algorithm for OLAP queries that effectively utilizes existing materialized views. The proposed algorithm can make use of materialized views having different selection granularities, selection regions, and aggregation granularities together to generate an efficient rewritten query.