2008-01-11
XML Everywhere?
I was recently asked, how widespread is the use of XML? I had to stop and think. It’s almost as if someone asked me how widely used is air, or perhaps more fairly how many socks there are in the world.
So here are some places where XML is used, and I’d like to invite people to leave comments suggesting other places where XML is used. You have to register to post a comment, to keep out spam (and they are moderated), but I promise not to do anything bad with your email address.
So, where is XML used? The first use case we had was for technical documentation, for aircraft manuals, telephone switch manuals, car manuals and a host of other documentation that was already using SGML. The manual in the glove compartment of your new GM car was produced using SGML or XML.
Speaking of cars, chances are high (50% or more) in North America that if you fill your car with petroleum, the messages from the pump to the cash register in the filling station’s office are sent using XML, validated with XML Schema too. And the diagnostic computer on board your car probably talks in XML to the garage mechanic. I have been unable to verify a rumour that XML messages are passed around between components when you put your foot on the brake pedal, but maybe the danger of sharp pointy brackets falling out of the pedals would discourage barefoot driving?
When you get home perhaps there is a bank statement waiting for you, and perhaps, like millions of others, it was made using XML and XSL-FO; the Financial industry is a heavy XML user, as is the Publishing industry.
Your mobile telephone may well be sending and receiving messages in XML more often than you realise; this is one of the motivations for the W3C Efficient XML Interchange work.
I’m told that some people browse the World Wide Web using mobile telephones; I have yet to see that being convenient or useful, or for tha matter significantly cheaper than buying a desktop PC, looking at the Web page, and then discarding the PC, but maybe someone will convince me. At any rate, Web services are of course being used widely in the Enterprise, and other spacecraft, and mobile phones can also view SVG graphics (another reason for wanting EXI!).
All of the major commercial relational databases have some form of XML support today, and of course it’s part of ISO SQL; there’s also a standard way to call XML Query (XQuery) from Java. Most of the open source relational databases appear to have fallen behind, although MonetDB does have XQuery support.
If you connect the financial industry the database industry and Web publishing, you get people like eBay, who are big XML users: when you view pages on www.ebay.com, you are looking at the result of some of their 4,000,000+ lines of XSLT and XQuery. Of course, a lot of Web sites are using XML on a back end somewhere; my own uses XML and XQuery for the image search, and it’s really not that unusual.
Did you know that Microsoft Windows components communicate with each other using XML? Try double-clicking on a .zxqp file that the OS doesn’t understand, and notice it asks if you want to use a Web service to contact Microsoft and try to identify the file.
But it’s not only Microsoft that’s using XML. OpenSolaris, OS X, BSD Unix and Linux, to name a few, all ship with XML support. For that matter many operating environments are using XML to store configuration information, ranging from the shape of the windows and text of dialogue buttons in applications through to preferences.
I’m sorry if I have not mentioned your favourite XML application or industry sector. Perhaps you can help me out by leaving a comment.
I’d say that almost all computers in use today have XML going on inside them, along with a significant proportion of mobile devices. And automobiles. Probably somewhere there are XML-enabled shoes, although since I’m usually barefoot I wouldn’t notice.
Why did XML succeed? I’ll leave that for another blog entry I think. For now let’s just say that it’s widely used, and if that’s a measure of success, we did well.