document: Performing grouping and aggregate functions in XML queries Since more and more business data are represented in XML format , there is a compelling need of supporting analytical operations in XML queries . Particularly , the latest version of XQuery proposed by W3C , XQuery 1.1 , introduces a new construct to explicitly express grouping operation in FLWOR expression . Existing works in XML query processing mainly focus on physically matching query structure over XML document . Given the explicit grouping operation in a query , how to efficiently compute grouping and aggregate functions over XML document is not well studied yet . In this paper , we extend our previous XML query processing algorithm , VERT , to efficiently perform grouping and aggregate function in queries . The main technique of our approach is introducing relational tables to index values . Query pattern matching and aggregation computing are both conducted with table indices . We also propose two semantic optimizations to further improve the query performance . Finally we present experimental results to validate the efficiency of our approach , over other existing approaches .
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