XML is flexible exchange format that has gained popularity for representing many classes of data, including structured documents, heterogeneous and semi-structured records, data from scientific simulations, digitized images, among others. As a result, querying XML documents has received much attention. XML documents are typically queried with a combination of value search and structure search. While querying by values can leverage traditional database technologies, evaluating structural relationship, specifically parent-child or ancestor-descendant relationship, between XML element sets has imposed a great challenge on efficient XML query processing. Many index-based approaches have been proposed for storing and efficient XML queries. This paper describe famous sort of storing tree , B~+ - tree, XR-tree, and XB-tree and analyzes how well they support XML query.
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