def _make_sro(object_generator, source_id, rel_type, target_id):
    """
    Make an SRO.

    :param source_id: The ID of the source object (string)
    :param rel_type: The relationship type (string)
    :param target_id: The ID of the target object (string)
    :return: The SRO, as a dict
    """

    rel = object_generator.generate("relationship")
    rel["source_ref"] = source_id
    rel["target_ref"] = target_id
    rel["relationship_type"] = rel_type

    return rel