CRITICAL SKILL 8.1 Understand XML

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Before we begin to see how Extensible Markup Language (XML) and Oracle Database 10g work together, we need to look at why XML is important for us and why Oracle has included significant support for XML in the Oracle XML DB. This chapter will discuss what XML is and why it is important to our computer futures. Additionally, we will show you how Oracle can become an integral part of all of your solutions that need to use XML.

CRITICAL SKILL 8.1
Understand XML

Most of you have visited countless web sites, have navigated to the menu bar at the top of a browser screen, and then selected View | Source. At this point, guess what you are looking at—html or hypertext markup language. As html became more and more popular, the most brilliant minds decided to extend the power of the language. They were specifically interested in designing a way to enhance HTML's functionality with a set of user-defined tags. A tag is simply a keyword bound by greater-than signs, less-than signs, and a specially placed forward slash. The following listing shows a few sample tags in html; the tags themselves are bolded.

<h1>Welcome to my level one header</h1>
<b>I like to bold text too, do you</b>
<font color=green size=+2>I am big and green</font>

That's all fine and dandy, but in a nutshell, XML allows you to extend the functionality of tags. Suppose you were coding a page for a real estate application and you wanted to custom-define your own tags to resemble the following:

<ground_floor>Family room . . .
. . . with wood-burning . . .
. . .
</ground_floor>

No big deal when you look at these primitive examples, but take our word for it—XML is a big deal. A markup language, of which HTML and XML are two, is a mechanism to identify structures in a document. Markup is also a term for metadata—that is, information about information. In short, an XML document can be defined as a document that can describe itself. Mature database products, of which Oracle Database 10g is the subject at hand, have the capability to store XML data types.

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