All Hail the Metator
This Wired article about a fanfiction site and how it got organized is a good way to understand the category/tag, top-down/bottom-up dichotomy. The site uses a combination of author provided meta and human evaluation:
On AO3, users can put in whatever tags they want. Then behind the scenes, human volunteers look up any new tags that no one else has used before and match them with any applicable existing tags, a process known as tag wrangling.
This is Bob Boiko’s concept of the “metator” come to life. Boiko presented this idea in his Content Management Bible almost 20 years ago. Here’s RSG commenting on the idea in 2009:
Metators are really contextualizers. They look beyond the item of information itself to understand things like its relationships, impact, trajectory, findability, alternate formats, and potential consumption profile.