Both XML-relational systems and native XML systems support creating XML wrapper views and querying against them. However, update operations against such virtual XML views in most cases are not supported yet.

The XML data is order-sensitive. The order problem, that is how ordered XML documents and order-sensitive queries over it can be efficiently supported when mapped into the unordered relational data model, has not yet been adequately addressed. In this paper, we present a general approach for supporting order-sensitive XQuery-to-SQL translation that works irrespective of the chosen XML-to-relational data mapping and the selected order-encoding method. Our approach, called XSOT, utilizes an order-aware XML algebra representation. We propose order-sensitive rewriting rules at the algebraic level to eliminate the dependency of the order determining operators on the implicit XML view order. Furthermore, we introduce a series of order-sensitive optimization steps to transform the XML algebra tree for the purpose of efficient SQL translation. Lastly, we utilize a template-based approach using SQL-99 order features to generate SQL statements.

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