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XQuery (XML Query) is a query and functional programming language that queries and transforms collections of structured and unstructured data, usually in the form of XML, text and with vendor-specific extensions for other data formats (JSON, binary, etc.). The language is developed by the XML Query working group of the W3C. The work is closely coordinated with the development of XSLT by the XSL Working Group; the two groups share responsibility for XPath, which is a subset of XQuery. XQuery 1.0 became a W3C Recommendation on January 23, 2007. XQuery 3.0 became a W3C Recommendation on April 8, 2014. XQuery 3.1 became a W3C Recommendation on March 21, 2017. "The mission of the XML Query project is to provide flexible query facilities to extract data from real and virtual documents on the World Wide Web, therefore finally providing the needed interaction between the Web world and the database world. Ultimately, collections of XML files will be accessed like databases." XQuery is a functional, side effect-free, expression-oriented programming language with a simple type system, summed up by Kilpeläinen: All XQuery expressions operate on sequences, and evaluate to sequences. Sequences are ordered lists of items. Items can be either nodes, which represent components of XML documents, or atomic values, which are instances of XML Schema base types like or . Sequences can also be empty, or consist of a single item only. No distinction is made between a single item and a singleton sequence. (...) XQuery/XPath sequences differ from lists in languages like Lisp and Prolog by excluding nested sequences. Designers of XQuery may have considered nested sequences unnecessary for the manipulation of document contents. Nesting, or hierarchy of document structures is instead represented by nodes and their child-parent relationships XQuery provides the means to extract and manipulate data from XML documents or any data source that can be viewed as XML, such as relational databases or office documents.

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XPath

XPath (XML Path Language) is an expression language designed to support the query or transformation of XML documents. It was defined by the World Wide Web Consortium (W3C) in 1999, and can be used to compute values (e.g., strings, numbers, or Boolean values) from the content of an XML document. Support for XPath exists in applications that support XML, such as web browsers, and many programming languages. The XPath language is based on a tree representation of the XML document, and provides the ability to navigate around the tree, selecting nodes by a variety of criteria.

Query language

A query language, also known as data query language or database query language (DQL), is a computer language used to make queries in databases and information systems. A well known example is the Structured Query Language (SQL). Broadly, query languages can be classified according to whether they are database query languages or information retrieval query languages. The difference is that a database query language attempts to give factual answers to factual questions, while an information retrieval query language attempts to find documents containing information that is relevant to an area of inquiry.

XQuery