More on tagging, taxonomies, folksonomies, etc.: Taxonomies and Tags Big concepts contain smaller ones that contain smaller ones yet. Over the millennia, we have fashioned the structures of knowledge in just such tree-like ways, from the departmental organization of universities (liberal arts contains history and history contains ancient Chinese history) to the hierarchy of species. The idea that knowledge is shaped like a tree is perhaps our oldest knowledge about knowledge. When it comes to innovation on the Internet, metadata is becoming the new content.

But traditional taxonomic trees aren’t something we can throw away without a thought. They are an amazingly efficient way of organizing complexity because they enable us to focus on one aspect (e.g., that’s an apple) while keeping a universe of context (it’s a fruit, part of a plant, a type of living thing) in the background, ready for access.

Traditionally, people have been loath to attach metadata to objects, because it felt like a chore without immediate benefit.

Both trees and faceted systems specify the categories, or facets, ahead of time. They both present users with tree-like structures for navigation, letting us climb down branches to get to the leaf we’re looking for. Tagging instead creates piles of leaves in the hope that someone will figure out ways of putting them to use[...]