Chapter 1. XQuery: A Guided Tour
XML (Extensible Markup Language) is an extremely versatile data format that has been used to represent many different kinds of data, including web pages, web messages, books, business and accounting data, XML representations of relational database tables, programming interfaces, objects, financial transactions, chess games, vector graphics, multimedia presentations, credit applications, system logs, and textual variants in ancient Greek manuscripts.
In addition, some systems offer XML views of non-XML data sources such as relational databases, allowing XML-based processing of data that is not physically represented as XML. An XML document can represent almost anything, and users of an XML query ...