  XML data warehouses form an interesting basis for decision-support
applications that exploit complex data. However, native-XML database management
systems (DBMSs) currently bear limited performances and it is necessary to
research for ways to optimize them. In this chapter, we present two such
techniques. First, we propose a join index that is specifically adapted to the
multidimensional architecture of XML warehouses. It eliminates join operations
while preserving the information contained in the original warehouse. Second,
we present a strategy for selecting XML materialized views by clustering the
query workload. To validate these proposals, we measure the response time of a
set of decision-support XQueries over an XML data warehouse, with and without
using our optimization techniques. Our experimental results demonstrate their
efficiency, even when queries are complex and data are voluminous.
