XML is used across proprietary and open software
What is it?
Extensible Markup Language (XML) is used to create specialist markup languages that can be read by both humans and machines. XHTML, HTML’s designated successor, is effectively HTML reformulated and extended in XML.
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A Worldwide Web Consortium (W3C) standard, XML has been adopted across the industry, from Microsoft to the open source community. Being platform-independent and licence-free, it enables data and information about the data to be shared and understood by many different systems. But some suppliers have been accused of implementing only partial XML support to maintain proprietary lock-in.
XML is spreading into new areas where people may be unaware that they are using it. RSS (Really Simple Syndication) newsfeeds use a lightweight XML.
An increasing number of roles expect some familiarity with XML, but this ubiquity also means that premium roles with XML are harder to come by.
Where did it originate?
Like other W3C markup languages, XML is a simplified subset of the rich but complex Standard Generalised Markup Language. Work began on what was to become XML in 1995, and XML 1.0 became a W3C recommendation in 1998.
What’s it for?
XML was devised as a way of defining document formats, and the early applications were in specialist publishing – from music and bibles to the petroleum industry. It is also used for document storage and processing.
The ability to create business documents that could be universally understood led to XML’s extension into e-business, where it rapidly made proprietary initiatives redundant.
XML can be used to represent data to people, to applications and databases, or to both. The data can be manipulated by Extensible Stylesheet Language Transformations (XSLT). However, the price of being universally understood is a much more disciplined approach to syntax than those from an HTML background may be used to.
What makes it special?
Being character- or text-based, in contrast to early proprietary data description initiatives, XML needs nothing more than basic text editing or word processing for authoring and maintenance.
However, human readability comes at a cost. XML’s syntax has been described as verbose, and documents can take up a lot of storage and bandwidth. There is quite a large “anti” camp: take a look at www.xmlsucks.org to see why “XML is technologically terrible but you have to use it anyway”.
How difficult is it to master?
XML is straightforward for those with a background in HTML and scripting languages. Document processing experience helps. It can be much harder for beginners; learning XHTML first is probably the best route.
What’s coming up?
The XML Cover Pages site has details of all the activities of the XML working groups and XML industry news.
Rates of pay
There is a huge range of job options for people with XML skills, from web designers to database developers, and rates vary accordingly.
The W3C site is not a great deal of help for those seeking XML training. You can try (as it suggests) a Google search, or go to the Microsoft or IBM Developerworks XML pages, or to independent sources such as O'Reilly's xml.com or the xml.org portal. There are plenty of free online tutorials - old ones are still good ones.
Basic XML classroom courses are on offer from £1,500 for three days to £1,500-plus for five days.
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