XML Introduction

What is XML? XML stands for EXtensible Markup Language, which became a W3C Recommendation on 10. February 1998. XML is a markup language which is like HTML. XML and HTML both use tags. But there are some differences between them:

• HTML was designed for how to display data. And XML was designed for how to store data.
• HTML tags are predefined (for example "<p>", "<table>", etc.). But XML tags are not predefined. You must define your own tags

Before you learn XML, you should have a basic understanding of HTML.

The following example is a product information, stored as XML:

<product>

<name>Garmin Oregon 300 3 inch' Touchscreen Handheld GPS Unit with a Built-in Basemap and Shaded Relief</name>
<category>GPS</category>
<brand>Garmin</brand>
<price>529.99</price>
<link>http://www.selectagps.com/Garmin-Oregon-300-3-Touchscreen-Handheld-GPS-Unit-with-a-Built-in-Basemap-and-Shaded-Relief-Electronics--d_B001B19XMS.html</link>
<description>handheld GPS navigator for use outdoors, in a car, or on a boat 3 inchLCD touchscreen display (240 x 400 pixels) with built-in picture viewer </description>

</product>

As you can see, it is just pure information wrapped in tags, which are not like HTML tags ("<table>", "<tr>", etc.) are predefined. You can create your own tags, like the ones in the above example, for your XML file.

XML can be used to simplify data storage and sharing. With XML, data is separated from HTML. So you can create HTML layouts for displaying data. When the data changes, you don't have to recreate your HTML file. With XML, data can also be easily exchanged between computer and database systems, even they are incompatible in any other ways. Because XML data is stored in text format, this makes it easier to export data from a system to an XML file, and then import it into another system. Before we have XML, the task of exchanging data between incompatible systems was not easier and complicated due to the different data formats. Now XML greatly reduces this complexity, and we can be easily expand or upgrade our operating systems and applications without losing data.

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