Complex Group-By Queries for XML

The popularity of XML as a data exchange standard has led to the emergence of powerful XML query languages like XQuery and studies on XML query optimization. Of late, there is considerable interest in analytical processing of XML data. As pointed out by Borkar and Carey, even for data integration, there is a compelling need for performing various group-by style aggregate operations. A core operator needed for analytics is the group-by operator, which is widely used in relational as well as OLAP database applications. XQuery requires group-by operations to be simulated using nesting.