/**
  * @access public
  * @param string
  * @param string
  */
 function register($type, $className)
 {
     $instance =& AggregateFactory::getInstance();
     if (!class_exists($className)) {
         Amber::showError('Warning', 'Missing declaration for class "' . $className . '", aggregate type = ' . $type);
         return false;
     }
     $instance->_classList[$type] = $className;
 }