XML - What is it ?

• XML is an acronym standing for eXtendable Markup Language. As you can see, the makers cheated on the name.
• XML is plain text, so any application can be made to collect data from it

XML is very similar to xHTML. In both, you have tags which are surrounded by the < sign and the > sign and they both have attributes. But that does not mean that XML can replace xHTML.


XML is hard to explain. It doesn't do anything, it holds data so other software can do things with it. xHTML is meant to display data, but you cannot use html do do something like send data to an application (you could, but it would not be practical). You could do this with a data format that just 'flew out of the sky' and is only used by that application, or you could use XML so that other applications can also easily access this information.

Writing XML is a lot like writing xHTML. You need a text editor, and you need a web browser (you don't need this but more on this later). Now, a lot of people like to use notepad to edit XML, but if you've been a good little newbie and have read m@teo21's tutorial on XHTML/CSS, you would have downloaded notepad++, a modern marvel. All you have to do in notepad++ is click the language drop-down menu, then go all the way down and click xml (should be second to the bottom) then presto! You're writing XML

now on to web browsers. You don't need them, but they help to tell you if your XML is valid. The xHTML/CSS tutorial should have taught you how to view xHTML documents in a web browser, and it should be exactly the same for XML. Just in case you forgot, here's how:

• save a file as .xml
• right click it and say "open with" then chick "Firefox" (or internet explorer etc)

So much work but now all you have to do to change it is save and click refresh on your browser.

I am going to give you a sample XML document so you can try:

This is correct: (note how the browser tells you it is correct)
Code: XML

And here is an incorrect code: (also note how the browser tells you it is incorrect)
Code: XML

These examples will be explained in the next chapter

There are a few very important things about XML to remember:

• in XML, you invent your own tags. xHTML wouldn't allow you to write a tag like <flavorofgum> to say what flavor of gum something was, but that's what XML is made for; to describe something like gum using tags like <flavor> and <price>
• XML is not meant to display things in web browser, so keep in mind, if your code looks ugly in the browser, that's just fine
• XML is everywhere. as a web developer, its probably beneficial to learn XML because it has so many practical uses

Because tags are names by you, they needed to write some rules. They couldn't let people write a tag called 'magic>pumpkin' (would look like <magic<pumpkin> ) or else the application would see the > and think the tag ended. So here they are

• names can only contain letters, numbers, and other characters.
• they cannot contain the words XML (or Xml or XMl ect)
• they cannot contain punctuation characters (eg. ! @ # $ % ^ & *)
• cannot contain spaces

Let's take a look at a very basic xml file

Code: XML

Looks familiar, doesn't it? In this example, we have 3 types of gum: grape, strawberry, and mint. The example includes price of gum, and the flavor. You can see that we have many elements (an element is a tag) inside other elements. This brings up something called an xml tree.

In this example the tree's roots are the 'root' element <gum>. All XML documents have a root elements, the root is a single element that all the other elements are in. Inside you can see the child elements of <gum> which are <type>. And inside the type elements are the <price> and <flavor> elements which are sub-childs of <gum>, and childs of <type>. So here's the basic structure of an xml document:

Code: XML

It's kind of like a tree: it has roots, branches (children), and leaves (sub-children). But the main problem with the tree is that trees don't get smaller than leaves (well, not if you want to get all technical about it) and in XML documents you can have children, sub-children, sub-sub-children, sub-sub-sub-children and so on.

Now that you have a taste of xml, it is time to go over syntax. The basic rules are identical to those of xHTML. For those who don't remember, here they are:

• all elements must have a closing tag
• all tags must be nested properly, this means they are closed in the opposite order they are opened: <child><sub-child></sub-child></child> and <child><sub-child></child></sub-child>
• tags are case sensitive. this meant <Gum> is not the same as <gum>
• all XML documents must be completely inside a root element
• you must use entity's in yore documents to write 'special' characters inside an element

Comments are very simple in xml, so i wont dwell on them to long. as in xHTML, comments are surrounded on both sides by a <!-- and a -->. Everything between these two will be ignored and turn green (they will also be in small text).

Well, I never said there were no attributes in XML, in fact, i never said anything about them at all.

The thing about attributes in xml is: there are better ways to get it done (some people may disagree but the majority works around them). Use elements instead.

You could say
Code: XML

but it is better to say
Code: XML

If you really must use attributes, the rules are the same as they are in xHTML:

• values must be in quotes
• you can create your own attributes (some could argue against that in xHTML )