def get_identifiers(sysmeta_pyxb):
    """Get set of identifiers that provide revision context for SciObj.

    Returns:   tuple: PID, SID, OBSOLETES_PID, OBSOLETED_BY_PID

    """
    pid = d1_common.xml.get_opt_val(sysmeta_pyxb, 'identifier')
    sid = d1_common.xml.get_opt_val(sysmeta_pyxb, 'seriesId')
    obsoletes_pid = d1_common.xml.get_opt_val(sysmeta_pyxb, 'obsoletes')
    obsoleted_by_pid = d1_common.xml.get_opt_val(sysmeta_pyxb, 'obsoletedBy')
    return pid, sid, obsoletes_pid, obsoleted_by_pid
Get set of identifiers that provide revision context for SciObj.

    Returns:   tuple: PID, SID, OBSOLETES_PID, OBSOLETED_BY_PID