def METHOD_NAME(self, ts, ts_next):
    """Create the descendant and progenitor links between two timesteps"""
    session = core.get_default_session()
    d_id = get_or_create_dictionary_item(session, "subfind_tree_link")
    obj_cache = timestep_object_cache.TimestepObjectCache(ts)
    obj_cache_next = timestep_object_cache.TimestepObjectCache(ts_next)
    links = self._create_links(ts, obj_cache_next, d_id, "Desc")
    links += self._create_links(ts_next, obj_cache, d_id, "Prog")
    session.add_all(links)
    session.commit()
    logger.info("%d links created between %s and %s",len(links), ts, ts_next)