/**
  * @return PermissionInterface
  */
 public static function getPermissionModel()
 {
     if (is_null(self::$model)) {
         $implementation = common_ext_ExtensionsManager::singleton()->getExtensionById('generis')->getConfig(self::CONFIG_KEY);
         if (is_object($implementation) && $implementation instanceof PermissionInterface) {
             self::$model = $implementation;
         } else {
             common_Logger::w('No permission implementation found');
             self::$model = new NoAccess();
         }
     }
     return self::$model;
 }
 /**
  * @param core_kernel_persistence_RdfsDriver $model
  */
 public static function setPermissionModel(PermissionInterface $model)
 {
     self::$model = $model;
     common_ext_ExtensionsManager::singleton()->getExtensionById('generis')->setConfig(self::CONFIG_KEY, $model);
 }