Structuring large PHP programs

What is the best practice for structuring a PHP program which is becoming too large to manage as a single file? Should it be broken into a number of includes, e.g.: switch ($whatever) { case 0: include('case0.php'); break; case 1: include('case1.php'); break; case 2: include('case2.php'); break; } or a number of functions: require('mylib'); switch ($whatever) { case 0: case0(); break; case 1: case1(); break; case 2: case3(); break; } Any thoughts, references to articles (couldn't find anything in PHPBuilder), etc gratefully received... Thanks - John