XML and its significance in the Web

XML (eXtensible Markup Language) is a W3C-recommended, text-based markup language in which users define their own tags to describe the structure and meaning of data. It is designed to store and transport data, is self-descriptive and independent of hardware, software and platform.

<book>
  <title>Web Technology</title>
  <author>A. Sharma</author>
  <price currency="NPR">650</price>
</book>

Significance of XML in the Web

• Data exchange and interoperability: Different systems (Java, PHP, .NET) can share data in a common, standard text format. Web services (SOAP, WSDL) use XML.
• Separation of data and presentation: HTML mixes content and display; XML keeps only data, and XSLT/CSS decide the presentation.
• Extensibility: New tags can be created for any domain, leading to languages such as XHTML, SVG, MathML, RSS, Atom and XAML.
• Self-describing, human- and machine-readable: Easy to understand, debug and process.
• Validation: DTD or XML Schema checks that data follows the agreed structure.
• Support for Unicode: Allows content in many languages, including Nepali.
• Foundation for the Semantic Web: RDF can be written in XML syntax (RDF/XML), adding meaning to web data.
• Data storage and configuration: Used in configuration files, document formats (docx, ODF) and databases.
• Tool support: Parsers (DOM, SAX) exist for all major languages.

Hence XML is a key technology for data sharing, web services and content syndication on the Web.