Stefan Mischook notes an update that he's made to his "Database Driven Websites" article he wrote up a while back:

The article explains the basic concepts behind dynamic websites, with the idea of making learning PHP that much easier. If you're new to the game (of PHP,) I would strongly suggest that you read this article.

This new version [pdf] includes the same great content as before with the addition of some new diagrams to help developers understand the concepts even easier.