/**
  * @brief set the group backend
  * @param  string  $backend  The backend to use for user managment
  * @returns true/false
  */
 public static function setBackend($backend = 'database')
 {
     // You'll never know what happens
     if (null === $backend or !is_string($backend)) {
         $backend = 'database';
     }
     // Load backend
     switch ($backend) {
         case 'database':
         case 'mysql':
         case 'sqlite':
             self::$_backend = new OC_Group_Database();
             break;
         default:
             $className = 'OC_GROUP_' . strToUpper($backend);
             self::$_backend = new $className();
             break;
     }
 }