Happy New Year, all.

Recently, I began learning XML through the W3C tutorial pages (http://www.w3schools.com/xml/default.asp). The tutorial states that the main function of XML is to describe data--not to display it. All right. This much I understand.

What else I understand is: XML elements, syntax, attributes and their qualities.

What I don't understand is the practical applications of XML. The example offered by the W3C (http://www.w3schools.com/xml/xml_real_life.asp) just doesn't make sense; it appears to be nothing more than an overcomplicated HTML document. Why would I use the code in the example if I could just create a simple HTML document? My best guess is that the HTML document could serve as the display for information sent to it by an XML document.

In all likelihood, I'm completely wrong.

Could someone please take the time clarify the matter for me? Again, what are the practical applications of XML?

Much thanks!

I have been really confused by the real purpose of XML too. I could be wrong, but from what I understand, it has to do with databases. XML is meta-data. And all meta-data is, is data that describes data. Databases use meta-data to organize and arrange data. So as far as I can tell, XML is useful for database driven sites.

I like to think of XML as 'database-markup-language' since that is essentially what it is. An XML schema or doctype definition is the equivalent of a database structure (the tables/columns and relationships). The XML file itself is a chunk of data that fits that schema. XML files can be displayed directly using a kind of XML style sheet although that's not really that useful. XML files are usually used as a format for data-interchange, especially between different companies since they just have to agree on a schema.

XML and all the associated extras like XSLT, XPath and XQuery etc were announced as the solution to all database problems ever, when in fact they are not really. Lots of database systems now provide support for XML import/export, however making queries on XML data can be a lot slower than a standard RDBMS like MySQL or SQL server having good indexes.

XML definitely has its uses - I've seen it used for config files, files saved from an application (MS Office is supposedly going to use an XML format in the future), CAD data files among other things. There are a number of standardised schema available for different uses such as SVG for graphics, MathML for mathematical formulae, MusicML for sheet music, DocBook for general text documents etc etc...

Just to back up what Oberon said and to add that XML is not dependent on a particular output so a document adhering to the rules of XML can be utilised in all kinds of applications including word processors, databases, servers, and even Web browsers. Due to its strictness it is easy to process and utilise using any programming language or database system.

There is no need to ditch xhtml if your purpose is only to create Web pages.
When using xhtml you are, in effect, using XML as xhtml is html re-defined using XML.

Also, just to clarify, w3schools has no connection with W3C.

XML is one of those buzz words that everybody hears about and gets all excited about then it just turns out to be another technology that has it's uses but isn't really anything special. It always makes me laugh driving past a certain building in my area with a big sign on it saying
"Software AG - The XML Company"
in huge letters. I've always wanted to knock on their door and ask, "So out of all the companies that deal with XML, what makes you the XML company?" It was probably just some non-techie manager who decided he liked the buzz word and to put it in their title.