Evaluating XML-extended OLAP queries based on a physical algebra

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. In this pa-per, we extend previous work on the logical federation of OLAP and XML data sources by presenting a simplified query semantics, a physical query algebra and a robust OLAP-XML query engine. Performance experiments with a prototypical implementation sug-gest that the performance for OLAP-XML federations is compara-ble to queries on physically integrated data