protected function getVersion($version)
    {
        if (!$this->{$version.'Version'}) {
            $revisioned = get_class($this->revisioned);

            $revision = new $revisioned();
            $revision->setRawAttributes($this->{$version});

            $this->{$version.'Version'} = $revision;
        }

        return $this->{$version.'Version'};
    }