So, you're writing the end-all, be-all application of your choice, and you keep running across the same problem with your program's structure - you want to use one function in another application, but can't figure out a good, clean way to get to it. One way to get around this kind of application bloat is to use "abstract classes" - and PHPBuilder.com has just the ticket to get you started.

For those that aren't aware, an abstract class is simply a base class that is not instantiated. In english, this just means that there's no code, but only defines what code needs to be availible to its subclasses. They give the example of having an abstract class be at the top of your class hierarchy - then it can provide functionality to all of it's subclasses.

So, using this kind of functionaility in PHP allows you to split up the load, and plan a bit more ahead when it comes to the layout of your classes. Defining a function in an abstract class allows you to be able to use that function from anywhere in your application (since it will always be defined), and allow you to think through more of your design. Remember - plan first, code later....