Extending Model class

[eluser]marcalj[/eluser]
Making a CMS I have to extend controller and model class.

The controller class was easy but the model class don't.

I have to put

Code:

include_once( APPPATH . "libraries/CMS_Model.php" );

in the header of every specific model I create.

Why I need to include main model class and don't in the extended controller ??

Thanks.