Algebra-Based Optimization of XML-Extended OLAP Queries

In today’s OLAP systems, integrating fast changing data, e.g., stock quotes, physically into a cube is complex and time-consuming. The widespread use of XML makes it very possible that this data is available in XML format on the WWW; thus, making XML data logically federated with OLAP systems is desirable. This report presents a complete foundation for such OLAP-XML federations. This includes a prototypical query engine, a simplified query semantics based on previous work, and a complete physical algebra which enables precise modeling of the execution tasks of an OLAP-XML query.
Effective algebra-based and cost-based query optimization and implementation are also proposed, as well as the execution techniques. Finally, experiments with the prototypical query engine w.r.t. federation performance, optimization effectiveness, and feasibility suggest that our approach, unlike the physical integration, is a practical solution for integrating fast changing data into OLAP systems.