4.2 XML (eXtensible Markup Language)
Whereas HTML was designed to format and display data, XML was designed to structure, store, and transport information, with the focus being on what that data is. XML became a W3C Recommendation in 1998 and is a compliment to HTML, not a replacement, and is easy enough to learn. In fact it is much like HTML, except that the tags are not predefined and must be defined by the web designer to suit. In addition, XML doesn't actually do anything; it is simply stored information. However, XML-aware applications can handle the XML tags in specific ways.
Again a simple text editor such as Microsoft Notepad can be used:
<?xml version="1.0"?> <note> <to>Alan</to> <from>Steve</from> <heading>Reminder</heading> <body>Bring your boots</body> </note>
In this example we have defined some tags called note, to, from and heading to store information regarding a reminder. Remember that this is simply information and will not actually do anything on its own. XML is simply a software and hardware-independent tool for carrying information, one that has tried to simplifies data exchange away from the many incompatible systems. Where it comes in handy for websites is for displaying dynamic content. Data can be stored in separate XML files and brought into HTML pages using Javascript. In addition to this, XML has been used to create new web languages, including XHTML, WAP, WML and RSS (for feeds).