XML Data Warehousing

Data warehousing is an important application of database technology. Even though XML is ubiquitous and there are many XML databases, there are almost no XML data warehouses today. When the information to be represented naturally has multiple dimensions, as in data warehouses, fundamental tensions appear in the modeling and schema design. This book propose an evolutionary extension of the XML data model into a multi-dimensional model, called the Multi-Colored Trees (MCT) logical data model. MCT permits trees with multi-colored nodes to signify participation in multiple dimensions. Algorithms are developed to transform design specifications given as ER diagrams into MCT schemas. Bitmap join indices are extended to the XML context. This book demonstrates experimentally the benefit for typical queries, including those with low cardinality or high selectivity. The book also considers the data cube, and shows that it cannot readily be expressed or evaluated for XML data. Specifically, XML data is not always summarizable because of missing and repeated sub-elements.