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A CDE Definition

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XML document

A file that contains text with interspersed descriptions, called "tags." All XML files are XML documents and vice versa. The XML document is often organized in a hierarchy with an "open" tag at the beginning of the file, a "close" tag at the end and all the text elements in between. Each text element has an open and close tag as well, and all tags begin with the less-than (<) character and end with the greater-than (>) character. See XML.

XML Tag Example
This example shows one definition from the XML feed for this encyclopedia. All the tags within the open and close "definition" tags are in a prescribed hierarchy. Note that all close tags have a slash (/) after the beginning less-than (<) symbol.


(EXtensible Markup Language) The most widely used semi-structured format for data, introduced by the W3C in 1998. XML files contain only tags and text similar to HTML. However, whereas HTML defines how elements are displayed and printed, XML assigns meaning to the elements. HTML uses predefined tags, but XML requires the developer of the content to define most of the tags. Thus, just like database records, virtually any data items, such as "product," "sales rep" and "amount due," can be specified.

By providing a common method for identifying data, XML supports business-to-business transactions and has become "the" format for electronic data interchange and Web services.

XML Is Only a Format
When introduced, XML was hyped as the panacea for e-commerce, but it was only a first step. The human-readable XML tags provide a simple format, but the intelligent defining of these tags to serve business needs properly and everyone's compliance in using the same tags determine XML's real value. Countless vocabularies have been developed for vertical applications; so many in fact, that a universal language was developed to provide a standard for interoperability between them (see UBL). See XML vocabulary, Web services, SOA and EDI).

XML Documents Can Define Themselves
An XML document can include a self-describing set of rules that identify the tags and their relationships; for example, only one XYZ tag is allowed within an ABC tag, or there must be one XYZ tag within every ABC tag and so forth. See XML schema.

More Rigid than HTML
Unlike HTML, which uses a rather loose coding style and is more tolerant of coding errors, XML pages have to be "well formed" and comply with the rules. See XSLT, DTD, DOM, XHTML, JSON, HTML, SGML, SMIL and XML-RPC.

Although similar, XML tags define data, whereas HTML tags define the page layout (in this example, font size and a bold date). All elements are wrapped within "start" and "end" tags, also called "open" and "close" tags. The tags themselves begin with a less-than (<) character and end with a greater-than (>) character. All end tags begin with less-than-slash (</).

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Before/After Your Search Term
XM RadioXML namespace
XM2goXML native database
XmarkXML Paper Specification
XMIXML parser
XMLXML pipeline
XML-DataXML processor
XML-Data ReducedXML Protocol
XML databaseXML repository

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