Title :Introduction to Abstract classes in PHP
Full Article: http://www.phphacks.com/content/view/35/33/

Recommended to : Beginner PHPer

Introduction: An abstract class is a class that cannot(or should not) be instantiated. This is an example of how to create an abstract class by the guy(s) from phphacks.com

Abstract:
Like the introduction said, you only need to ensure this class can't be instantiated. The first version is make an class with a prototype function. The prototype function contains die() command, so when the class it's called, the script simply dies. To improve the code, trigger error is used instead of die. A new conditional test tests if the class called is the abstract class by using a constant _CLASS_. Now this class can't be instantiated by anything other than its subclass. In the final script, a conditional check for the subclass is added. _CLASS_ is replaced with get_class($this).

Facts from Conclusion:

• Abstract class are classes can't be instantiated.
• Use get_class($this) insted of the _CLASS_ constant.

Editor Comment:

What's the point of making a class can't be instantiated? I don't know. I was never in a position where I have to organize a well-structured hierarchy. Will you ever need to use abstract classes? I don't know :) But you could learn something about improving coding though this tutorial