On PHPBuilder.com today there's a new tutorial that talks about creating interfaces in PHP and how to use them to effectively structure your application.

Starting with PHP 5 the object model was rewritten to add features and bring PHP in line with languages such as Java and Visual Basic .NET. In this article I'll discuss interfaces, which is among the most important features in PHP 5. Other important features include abstract and final classes, methods and additional magic methods. You will learn how to define your own interfaces and how to work with them using different object model mechanisms.

The introduce you to some of the basic concepts behind using interfaces and how to create a basic one - a simple definition of a string class with one method, "getString". They then show how to extend a different example (a RandomNumber interface) and add on an additional method. He also shows how to extend multiple interfaces and integrate functionality from multiple sources, overloading and overrides.