A Query Processing Architecture for an XML Data Warehouse

Data warehousing accounts for a significant fraction of database use today. As XML becomes ever more popular, more and more XML data finds its way into data warehouse repositories. This paper examines the modeling mismatch between the tree structure of XML data model and the multidimensional model of a typical data warehouse, and proposes an XML warehouse model based on the multi-colored trees (MCT) logical data model that resolves the modeling issue naturally. Furthermore, this data model ameliorates some well-known modeling limitations of the XML data warehouse. To cope with ad-hoc OLAP queries, we extend bit-map join indices to the XML context. We then tackle the difference between the bit-map and the stack-based structural join processing paradigm popular in XML query processing, permitting both styles of query processing to be used seamlessly in consort to evaluate queries. We demonstrate experimentally the benefit of bit-map join indices for typical queries, and particularly those with low cardinality or high selectivity.