def _gnurl( clientID ):
    """
    Helper function to form URL to Gracenote_ API service.
    
    :param str clientID: the Gracenote_ client ID.
    :returns: the lower level URL to the Gracenote_ API.
    :rtype: str
    """
    clientIDprefix = clientID.split('-')[0]
    return 'https://c%s.web.cddbp.net/webapi/xml/1.0/' % clientIDprefix