def is_job_ref(thing, reftype=dict):
    '''
    :param thing: something that might be a job-based object reference hash
    :param reftype: type that a job-based object reference would be (default is dict)
    '''
    return isinstance(thing, reftype) and \
        ((len(thing) == 2 and \
              isinstance(thing.get('field'), basestring) and \
              isinstance(thing.get('job'), basestring)) or \
             (len(thing) == 1 and \
                  isinstance(thing.get('$dnanexus_link'), reftype) and \
                  isinstance(thing['$dnanexus_link'].get('field'), basestring) and \
                  isinstance(thing['$dnanexus_link'].get('job'), basestring)))