On Elated.com there's a new introduction to working with inheritance in PHP for object-oriented applications. They work through some of the basic concepts including parent/child classes, final and abstract classes and interfaces.

In this article we're going to explore the idea of inheritance in object-oriented programming, and how inheritance works in PHP. With inheritance, your objects and classes can become much more powerful and flexible, and you can save a lot of time and effort with your coding.

They start with the basics of how inheritance works and then move right into creating child classes from a parent. Their example code makes a basic forum system (just example code, not fully functioning) with administrators, members and forum creation. They use this as a base to show the method overriding and exposure with "final". The finish it off with examples of two things that can promote good application structure - abstract classes an interfaces.