I added a series system to my Books page and assigned every applicable book to a series. I'm not entirely sure I've done every book correctly; there are many disagreements and there are many hard-core fans, so there are many ways to do it. I've toyed with the idea of also assigning every book with a series to a universe, where series is a subset of (and completely enclosed by) universe. For instance, Ringworld is now in the Known Space series, but arguably that's the Known Space universe, where the series is the eponymous Ringworld series. And to further complicate things, authors sometimes merge series, as in Asimov's Robot series which merges into the Empire series which merges into the Foundation series. Some people even sub-divide the Foundation series into Pre-Foundation, Foundation, and End-Foundation. And then there's the problem of parallel series, as in Orson Scott Card's Ender's Game novels, which run parallel to his Ender's Shadow novels. And all of those combined might be said to reside in the Enderverse. Oy vey!