def make_key(element_name, element_type, namespace):
    """Return a suitable key for elements"""
    if element_type in ('complexType', 'simpleType'):
        eltype = 'complexType'
    else:
        eltype = element_type
    if eltype not in ('element', 'complexType', 'simpleType'):
        raise RuntimeError('Unknown element type %s = %s' % (element_name,
            eltype))
    return element_name, eltype, namespace
