Optional forests of hierarchy trees are where it's at. Essentially don't encode everything into one gigantic one. Sometimes you know that users are going to ta

Optional forests of hierarchy trees are where it's at. Essentially don't encode everything into one gigantic one. Sometimes you know that users are going to tag `laptop` a bunch and want that to also drag in `personal computer` (but not all `PC`s are `laptop`s) or that `blue dress` is also a `dress` and don't want to hard code special cases. That said, if you are going to do this, then you must have it controlled by an admin/moderator. Maybe allow for hierarchy request submissions but have it moderated. There is at least one public system where this just works to my knowledge and a bunch of self-hosted ones as well.