Updating recursive xml views of relations
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XML is an extremely versatile markup language, capable of labeling the information content of diverse data sources including structured and semi-structured documents, relational databases, and object repositories.
A query language that uses the structure of XML intelligently can express queries across all these kinds of data, whether physically stored in XML or viewed as XML via middleware.
It is also flexible enough to query a broad spectrum of XML information sources, including both databases and documents.XPath syntax is used in several XML-related applications including XSLT [XSLT] and XPointer [XPointer].In XQuery, the result of a path expression is an ordered list of nodes (of course, each node includes its descendant nodes, so the result can be thought of as an ordered forest.) The top-level nodes in the path expression result are ordered according to their position in the original hierarchy, in top-down, left-to-right order.An alternative, XML-based syntax for the XQuery semantics will be defined separately.
XQuery is derived from an XML query language called Quilt, which in turn borrowed features from several other languages.
From SQL [SQL] it took the idea of a series of clauses based on keywords that provide a pattern for restructuring data (the SELECT-FROM-WHERE pattern in SQL).