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Section I: An Introduction to XML

Welcome to the fast-paced and exciting world of XML programming!  Surely you don’t want to waste any time with unneeded things such as code or syntax, so… oh, wait, maybe you do want to cover syntax and code.  Pretty fortunate, really, considering that XML is code and syntax… but more on that in a minute.

So what is XML, anyway?

XML is the latest in a long line of programming languages that have been used to define pages on the World Wide Web. The letters “XML” stand for “eXtensible Markup Language”… and yes, it should technically be “EML” instead of “XML”, but the “X” makes it look a bit more cutting edge, so it stuck.  But what does “Extensible Markup Language” mean?

First, let’s define the term, “Markup Language”, which is the “ML” in many of the common (and some of the uncommon) programming languages that you’ll find used with the Internet.  At its most basic, a Markup Language is simply a type of programming code that tells a program how to display information.  The programs that are being told how to display the information are known as “Browsers,” and they really do need to be told how to display information or they just start shoving as much information into as small of a space as possible.

Here’s an example of how a Markup Language helps to display information.  Let’s say that you want to tell the world about your two cats, Tooter and Shade.  You type three sentences in a file, about like this:

                        Tooter is a fat, fuzzy black cat.

                        Shade is a slightly thinner short-haired gray cat.

                        Both of the cats are spoiled rotten.

When you load the file into a browser, though, what you see looks more like this:

Tooter is a fat, fuzzy black cat.Shade is a slightly thinner short-haired gray cat.Both of the cats are spoiled rotten.

The browser didn’t know how to format the information, so it just shoved it all together.  Instead of simply listing the information, try putting in a few extra characters, known as tags.

Tooter is a fat, fuzzy black cat.</p>

           

Shade is a slightly thinner short-haired gray cat.</p>

Shade is a slightly thinner short-haired gray cat.<

           

Both of the cats are spoiled rotten.

Both of the cats are spoiled rotten.

 

When you load this new file into your browser, you’ll end up with the original result that you intended.  The tags you added tell the browser that each line should be a paragraph of its own, and should have a blank line after it.

The basic language used to create most web pages (and is what we used in the example about Tooter and Shade) is known as HTML, or the “HyperText Markup Language.”  Though it sounds like something out of a bad 50’s science fiction movie, all that HyperText means is that there is a text document in an electronic form.  HTML uses text documents to tell the browser exactly how it should display the various files that the HTML document references.  These files can be images, other HTML documents, or even movies or music files.  (Oh, and for you trivia buffs out there… HTML was invented in 1990 by Tim Berners Lee, a physicist who was looking for a way to cross-reference text and information through hypertext links on the early version of the Internet.)

Unfortunately, HTML has its limitations.  These limitations have been greatly increased by the introduction of other languages, such as JavaScript, DHTML (Dynamic HTML), CSS (Cascading Style Sheets, which you’ll hear more about later), and ASP (Active Server Pages).  Even with all of these expansions, though, there’s still only so much that you can do with the basic tags and code of HTML.  That’s where XML comes in.

XML, like HTML before it, is a Markup Language… but it’s also so much more.  It’s the “X” that makes it special; XML isn’t limited by the tags it was created with, and can be expanded with custom tags to create effects that would sometimes take several lines of code in HTML (if the effects could be created at all.)