"So merely by putting the DVDs next to another on a shelf, you get a self-maintaining list of them."
I'm currently trying to organise my nearly 2,000 DVD's - so that similar ones are on the same shelf. Now - does "The Rocky Horror Show" go in fantasy, sci-fi, horror, or musicals?
Then again "Flash Gordon" is definitely for the children's section - but also could go in the sci-fi group. On the other hand "Flesh Gordon".....
I'll settle for an Excel-style spreadsheet with multiple category tags and an indicator to a physical shelf. With that I can put it on a tablet and check a DVD title in the charity shop - before mistakenly adding it to my collection for the second or more times.