XML stands for eXtensible Markup Language and is now a standard used to develop applications. Do not confust XML and HTML, while HTML is used to display data, XML is used to represent it. XML is also a tag based language, where you can develop your own tags to hold custom information. Here is an example of an XML tag
<code>
<Person>
<Name>Greg Georges</Name>
<Address>44 lala boulevard</Address>
<Age>23</Age>
</Person>
</code>
This is a simple example of XML. You can use DTD's to validate your XML. Then, XSL (eXtensible Stylesheet Language) can be used to extract the data from the XML into webpages, HTML can be mixed into the XSL.
Now, what is the use of this great technology. The possibilites are almost endless. I use XML to configure my
Java apps instead of property files. All you need is a good XML parser for Java. Sun has JAXP and I use Apache's Xerces. Also, XML files can be used to transfer data from 2 different applications. Example, make a Java app communicate with a legacy system written in C. All you need are parsers on each side and that is it. I suggest learning XML as soon as possible, I read Java and XML by Brett Mclaughhlin, real good book. Anyways, have fun!