  As XML becomes ubiquitous and XML storage and processing becomes more
efficient, the range of use cases for these technologies widens daily. One
promising area is the integration of XML and data warehouses, where an
XML-native database stores multidimensional data and processes OLAP queries
written in the XQuery interrogation language. This paper explores issues
arising in the implementation of such a data warehouse. We first compare
approaches for multidimensional data modelling in XML, then describe how
typical OLAP queries on these models can be expressed in XQuery. We then show
how, regardless of the model, the grouping features of XQuery 1.1 improve
performance and readability of these queries. Finally, we evaluate the
performance of query evaluation in each modelling choice using the eXist
database, which we extended with a grouping clause implementation.
