  The aim of this article is to present an overview of the major XML
warehousing approaches from the literature, as well as the existing approaches
for performing OLAP analyses over XML data (which is termed XML-OLAP or XOLAP;
Wang et al., 2005). We also discuss the issues and future trends in this area
and illustrate this topic by presenting the design of a unified, XML data
warehouse architecture and a set of XOLAP operators expressed in an XML
algebra.
