Extensible Markup Language (XML) is a markup language that defines a set of rules for encoding documents in a format which is both human-readable and machine-readable.
XML is a software- and hardware-independent tool for storing and transporting data.
XML plays an important role in many IT systems.
For this reason, it is important for all software developers to have a good understanding of XML.
Before you continue, you should also have a basic understanding of:
What is XML?
XML stands for EXtensible Markup Language
XML is a markup language much like HTML
XML was designed to store and transport data
XML was designed to be self-descriptive
XML is a W3C Recommendation
XML Does Not DO Anything
Maybe it is a little hard to understand, but XML does not DO anything.
This note is a note to Jack, from Jill, stored as XML:
<note> <to>Jack</to> <from>Jill</from> <heading>Reminder</heading> <body>Don't forget me this weekend!</body> </note>
The note is quite self-descriptive. It has sender and receiver information. It also has a heading and a message body.
But still, this XML document does not DO anything. XML is just information wrapped in tags. Someone must write a piece of software to send, receive, store, or display it:
Don't forget me this weekend!
The Difference Between XML and HTML
XML and HTML were designed with different goals:
XML was designed to carry data - with focus on what data is
HTML was designed to display data - with focus on how data looks
XML tags are not predefined like HTML tags are
XML Does Not Use Predefined Tags
The XML language has no predefined tags.
The tags in the example above (like and ) are not defined in any XML standard. These tags are "invented" by the author of the XML document.
HTML works with predefined tags like p, h1, table, etc.
With XML, the author must define both the tags and the document structure.
XML is Extensible
Most XML applications will work as expected even if new data is added (or removed).
Imagine an application designed to display the original version of note.xml ( ).
XML Simplifies Things
It simplifies data sharing
It simplifies data transport
It simplifies platform changes
It simplifies data availability
Many computer systems contain data in incompatible formats. Exchanging data between incompatible systems (or upgraded systems) is a time-consuming task for web developers. Large amounts of data must be converted, and incompatible data is often lost.
XML stores data in plain text format. This provides a software- and hardware-independent way of storing, transporting, and sharing data.
XML also makes it easier to expand or upgrade to new operating systems, new applications, or new browsers, without losing data.
With XML, data can be available to all kinds of "reading machines" like people, computers, voice machines, news feeds, etc.
XML is a W3C Recommendation
XML became a W3C Recommendation on February 10, 1998.