XML is perhaps one of the Internet's greatest unrecognised success stories. The first draft of the XML standard dates back only to 1996, and was born out of an attempt to marry the simplicity of HTML with the power of Standard Generalised Markup Language (SGML). It has rapidly moved centre-stage, to the point where most of the initiatives in the W3C A to Z list on its home page are based around XML - even HTML has been re-cast as XHTML.
But XML is more than just an exercise in re-packaging. Since its creation, the scope of XML has widened enormously, and now encompasses a number of major ancillary projects that address deeper technical issues well beyond simply tagging data more intelligently - XML's starting point. For example, the eXtensible Stylesheet Language (XSL) family - XSL Transformations (XSLT), XML Path Language (XPath) and XSL Formatting Objects (XSL-FO) - is concerned with the presentation side of XML documents: converting them into HTML for display in a browser is one obvious application.
Another aspect is represented by XML Linking - XML Linking Language (XLink), XML Base and XML Pointer Language (XPointer) - which tackles the complexities of how to jump within and between XML documents, and enables the creation of links that are considerably more sophisticated than HTML's unidirectional hyperlinks.
But just as important as this general work on fundamental technologies are the specialised applications of XML. A listing of these can be found as part of the Cover Pages, an extraordinarily comprehensive set of reference resources reporting on every aspect of XML and SGML, and one of the Web's enduring treasures.
The diversity of the applications is striking - and probably a major reason why XML's achievement is under-appreciated today. After all, who, other than those working in the field, is aware of the existence of ParlML - A Common Vocabulary for Parliamentary Language? Or the Weather Observation Definition Format and the Historical Event Markup and Linking Project - to say nothing of the Robotic Markup Language, Sports Markup Language and Spacecraft Markup Language? As the Cover Pages indicate, there are hundreds, soon to be thousands, of these kinds of languages being created, but most remain completely invisible to the general Internet user.
One application of XML does seems destined for more widespread appreciation, since it concerns an area that touches nearly everyone in business: accounting. The eXtensible Business Reporting Language (XBRL) differs from other financial XML applications - such as FpML, FinXML and OFX - that are concerned with transactions, by concentrating on the identification and reporting of corporate business information. There is some background information, a FAQ and technical resources.
As the progress reports indicate, XBRL is beginning to catch on around the world. For example, in the UK, the Inland Revenue is looking to use XBRL for the filing of corporation tax returns. Meanwhile, in the US, Microsoft is not only supporting the standard through its Office suite, but also employs XBRL for its own reporting.
Glyn Moody welcomes your comments.