XML Introduction

XML History


XML Syntax

XML Elements

XML Attributes

XML Validation


Extensible Markup Language (XML) is a simple, very flexible text format derived from SGML (ISO 8879). Originally designed to meet the challenges of large-scale electronic publishing, XML is also playing an increasingly important role in the exchange of a wide variety of data on the Web and elsewhere.

Extensible Markup Language (XML) is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards.

XML's design goals emphasize simplicity, generality, and usability over the Internet. It is a textual data format with strong support via Unicode for the languages of the world. Although the design of XML focuses on documents, it is widely used for the representation of arbitrary data structures, for example in web services.

Many application programming interfaces (APIs) have been developed that software developers use to process XML data, and several schema systems exist to aid in the definition of XML-based languages.

XML is not a replacement for HTML.

XML and HTML were designed with different goals:
  • XML was designed to transport and store data, with focus on what data is
  • HTML was designed to display data, with focus on how data looks
  • HTML is about displaying information, while XML is about carrying information.
Maybe it is a little hard to understand, but XML does not DO anything. XML was created to structure, store, and transport information.

The tags in the example above (like and ) are not defined in any XML standard. These tags are "invented" by the author of the XML document.

That is because the XML language has no predefined tags.

The tags used in HTML are predefined. HTML documents can only use tags defined in the HTML standard.

XML allows the author to define his/her own tags and his/her own document structure.

XML is now as important for the Web as HTML was to the foundation of the Web.

XML is the most common tool for data transmissions between all sorts of applications.

If you need to display dynamic data in your HTML document, it will take a lot of work to edit the HTML each time the data changes.

With XML, data can be stored in separate XML files. This way you can concentrate on using HTML for layout and display, and be sure that changes in the underlying data will not require any changes to the HTML.

With a few lines of JavaScript code, you can read an external XML file and update the data content of your web page.

Because of the lack of SGML support in mainstream Web browsers, most applications that deliver SGML information over the Web convert the SGML to HTML. This down-translation removes much of the intelligence of the original SGML information. That lost intelligence virtually eliminates information flexibility and poses a significant barrier to reuse, interchange, and automation.

For this reason, XML (Extensible Markup Language) was developed by the XML working group (known as the SGML Editorial Review Board) formed under the auspices of the World Wide Web Consortium (W3C) in 1996. XML is a highly functional subset of SGML. The purpose of XML is to specify an SGML subset that works very well for delivering SGML information over the Web. When the mainstream Web browsers support XML, it is believed that itís going to be very easy to publish SGML information on the Web. It's actually misnamed because XML is not a single Markup Language. It is a metalanguage to let users design their own markup language.

XML is a public format and not a proprietary format of any company. The v 1.0 specifications was accepted by the W3C as Recommendation on February 10, 1998.

XML was conceived as a means of regaining the power and flexibility of SGML without most of its complexity. While retaining the beneficial features of SGML, XML removes many of the more complex features of SGML that make the authoring and design of suitable software both difficult and costly. But XML also lacks some important capabilities of SGML that primarily affect document creation, not document delivery. Thatís because XML was not designed to replace SGML in every respect.

The question that is open is not whether XML will succeed as a widespread data format, but rather how fast, to what level of success and with what products. The question of whether XML would enter the market was answered when Microsoft, Adobe, Netscape and other big market players not only supported the development of the new standard but began making sizable product investments to this new format. The leading Web browser Products already support XML in their latest releases. The momentum building behind the XML effort means that XML is inevitably destined to become the mainstream technology for powering broadly functional and highly valuable business applications on the Internet, intranets, and extranets.

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