Extensible Markup Language

Extensible Markup Language
Name	Extensible Markup Language
Caption	XML document example
Developer	World Wide Web Consortium
Released	1998
Latest	1.0 Fifth Edition
Type	Markup language

Extensible Markup Language is a flexible markup language developed to facilitate structured data interchange across disparate systems such as Microsoft Corporation, Sun Microsystems, Oracle Corporation, IBM, and Netscape Communications Corporation. It emerged from work by the World Wide Web Consortium and related participants including the Internet Engineering Task Force and the W3C XML Working Group to bridge formats used by Hypertext Markup Language, SGML, UML, and CORBA-based middleware. Early adopters included Apache Software Foundation projects, Mozilla Foundation, and enterprise platforms like SAP SE and PeopleSoft.

History

The language was formalized in 1998 after discussions at the World Wide Web Consortium and technical inputs from vendors such as Microsoft Corporation, Sun Microsystems, Netscape Communications Corporation, IBM, and standards bodies including the Internet Engineering Task Force and the ISO. Influences trace to Standard Generalized Markup Language implementations and research by groups at MIT, Stanford University, Bell Labs, and Xerox PARC. Subsequent editions and errata were overseen by W3C editors and contributors from Oracle Corporation and Adobe Systems, with the specification intersecting with initiatives like XML Schema work and the development of SOAP and WSDL in consortiums including OASIS and the W3C Web Services Activity.

Design and Syntax

XML uses a nested element model derived from Standard Generalized Markup Language principles championed by researchers at IBM and Hewlett-Packard. Documents consist of prolog, elements, attributes, and character data compliant with Unicode ranges defined by the Unicode Consortium. Namespaces were introduced to resolve name collisions in composite vocabularies used by projects at Microsoft Corporation, Oracle Corporation, and Sun Microsystems; this concept was formalized through W3C recommendations and implemented in parsers from Apache Software Foundation and Mozilla Foundation. The grammar is specified with productions akin to those used by ISO standards and validated via grammars such as XML Schema, RELAX NG, and Document Type Definition formats developed by working groups including W3C XML Schema Working Group and contributors from OASIS.

Core Technologies and Standards

Core specifications surrounding the language include the primary W3C Recommendation, the XML Namespaces recommendation, the XML Schema specification, and the XPath and XSLT standards produced by the W3C XSLT Working Group. Complementary standards and protocols such as SOAP, WSDL, and RSS were advanced by organizations like OASIS and the W3C Web Services Activity and implemented by vendors including Microsoft Corporation, IBM, and Sun Microsystems. Validation and transformation toolchains often combine XPath, XSLT, XQuery (from the W3C XML Query Working Group), and schema languages like RELAX NG developed by groups including OASIS and independent projects at Nokia and Oracle Corporation.

Implementations and Software Support

A broad ecosystem of parsers, libraries, and tools supports the language across platforms: Apache Xerces and Apache Xalan from the Apache Software Foundation, Microsoft .NET Framework XML libraries, Oracle XML DB, and XML toolkits in languages endorsed by organizations such as Python Software Foundation (via ElementTree and lxml), Eclipse Foundation plug-ins, and Mozilla Foundation-based projects. Enterprise integration products from SAP SE, IBM WebSphere, and Oracle Corporation include XML processing stacks; open source databases like PostgreSQL and MySQL provide XML functions influenced by the W3C specifications. Publishing tools from Adobe Systems and content management systems developed by firms like Drupal Association integrate XML workflows standardized by the World Wide Web Consortium.

Applications and Use Cases

The language is used in syndication formats such as RSS, in configuration formats for Apache HTTP Server modules, and in web services stacks including SOAP and WSDL used by Microsoft Corporation and IBM for enterprise APIs. It underpins document standards like Office Open XML and has been employed in publishing standards developed by OASIS and organizations such as ISO for interchange of technical documents. Scientific data exchange initiatives at NASA, European Space Agency, and research institutions like CERN and National Institutes of Health have adopted XML vocabularies, while standards for geospatial interchange from Open Geospatial Consortium and legal document formats in initiatives by United Nations agencies use XML-based schemas. Tooling for transformation and querying—XSLT, XQuery, XPath—is embedded in stacks provided by Oracle Corporation, IBM, and the Apache Software Foundation.

Criticisms and Limitations

Critiques have focused on verbosity and processing overhead compared to binary or domain-specific formats developed by vendors such as Google and Facebook; competitors and alternatives like JSON and Protocol Buffers from Google are cited in discussions by implementers at Mozilla Foundation and Microsoft Corporation. Performance concerns in high-throughput systems prompted the creation of binary XML initiatives and streaming APIs promoted by the W3C and industry groups including OASIS. Debates involving contributors from Sun Microsystems, IBM, and Microsoft Corporation addressed complexity introduced by multiple schema languages and namespace mechanisms, leading to simplified alternatives adopted in RESTful designs championed by practitioners in the IETF and companies like Amazon.com.

Category:Markup languages