The Zend_Loader class includes methods to help you load files
dynamically.
Zend_Loader vs. require_once()
The Zend_Loader methods are best used if the filename you need to
load is variable. For example, if it is based on a parameter from
user input or method argument. If you are loading a file or a
class whose name is constant, there is no benefit to using
Zend_Loader over using traditional PHP
functions such as require_once().