Efficient grouping and ordering processing on XML data

Processing grouping operations on XML data has become an important research issue. In this article, we propose the notion of the structure group to represent a set of XML elements or attributes which are structure-related, and might correspond to the same set of answers. Such notion is used to design two indices. First, the group index is proposed to efficiently identify the structure group satisfying the value constraint. The value index can then retrieve the required value for a particular group. We also design the structure Grouping and Ordering Tree to represent the intermediate result in the properly nested and ordered structure, so that it can be easily transformed to the final result. A series of experiments have been performed, and the results show that the proposed index-based method is more efficient than the previous Scan approach, which scans the whole XML document and is based on the hashing technique.