What is XML?

If you are a blogger, you probably came across the term XML before. It is all over the place. But what is XML after all? And more importantly, should you care about it?

XML stands for Extensible Markup Language. Basically, it is a markup language created to transport structured data across different systems and platforms. There is an article over W3C titled “XML in 10 Points,” which gives an introduction to this language. The 10 points are:

XML is for structuring data
XML looks a bit like HTML
XML is text, but isn’t meant to be read
XML is verbose by design
XML is a family of technologies
XML is new, but not that new
XML leads HTML to XHTML
XML is modular
XML is the basis for RDF and the Semantic Web
XML is license-free, platform-independent and well-supported

After reading the article you realize why you should care about XML (or at least understand how it works). XML was created to facilitate the use of structured data across the Internet, and it is already becoming the standard for applications and platforms that try to accomplish that.
RSS, for instance, is just a modified XML format which carries the headlines and main content of your blog.

Notice that XML will not substitute HTML, but rather complement it. HTML is concerned with how data looks (on a website, for instance), while XML is concerned with describing the data itself and its structure.

The main difference between these two markup languages is that HTML has fixed tags, while in XML the tags need to be defined by the user or by the platform (that is why it is called extensible).

Many people think that Web 3.0 will be the semantic web. We can’t say for sure, but XML will probably be there, as the standard tool for transferring data across the Internet.
If you are interested you can read more about it on Wikipedia and on XML.com.