BookBrainz doesn't have a method that works well for modeling franchises and subfranchises, which can contain several independent and related series. I'm not sure the best way to handle franchises like Star Wars and Star Trek. Currently, it's not possible to emulate franchises with series since series-series relationships don't exist, although that could be one solution when they do. Alternatively, perhaps a new franchise entity could be used to solve this. This came up in the Matrix chat specifically for Star Trek: The Next Generation.