[Narf]

If your using a class library then you need to access external methods using the CI Super Object.

Code:

class yourClass
{
   private $_ci;

   public function __construct()
   {
       parent:: __construct();

       $this->_ci = get_instance();
   }
}

// access db and models using $this->_ci->db->get() etc;

This code will trigger a fatal error. There's no 'parent' to call when you don't extend anything.