Folk music has nothing to do with country.
Country was invented in the 1800s by a businessman who aimed it at primarily white Americans. Folk music has a rich history dating before the 1200s and before much of written language. Many songs of Irish and Welsh descent date before record, still being played today.
Nevertheless, to answer your question:
1) metatags, parent tags, and the like provide ways to structure tag relationships to encompass and describe what you speak of.
2) There are many networks out there that share user's tags based on file hashes. A system could scrape these networks for existing tags and autotag many items without the user's interaction (beyond initiating the autotagger). Users could also get their hands dirty and ask for only tags relating to parent categories, or something like that.
> Folk music has nothing to do with country.
I think the point was that they're both "music"; congrats, now you have a hierarchy again!
The word "folk" also denotes recognizeable format in the context of commercial broadcasting and streaming of canned music. It basically refers to a locus roughly centered around someone crooning while strumming chords on an acoustic guitar.
That's a very american-centric view you have there.
and any tagging scheme sufficiently good enough to describe the real world will implicitly create a hierarchical ontology
"A glass of juice is certainly a drink, but it is also a source of nutrition -- but not every drink is. There's not much nutrition in a glass of water. Likewise, there are many sources of nutrition which are not drinks. [...] A cup of tea is technically a source of energy (it is hot, it contains thermal energy), but so is a battery. Do they have a common base class?"[1]
(I remember a better example using soft drinks, but I couldn't find it with a quick google)
Say you're tagging hundreds of academic papers, so you have top-level tags math, physics, computer-science, graphics, machine-learning. Each of these has many subfields, and there is significant overlap between many of those. Perhaps more importantly, there is unpredictable future overlap, so it is generally impossible to define mutually exclusive categories (i.e. conventional directories [not counting links]) that are future-proof. I like to be able to define each hierarchy separately, then freely apply tags from any hierarchy to any item.
That's just one group of related hierarchies, and other categories of items (mutually exclusive categories DO exist, with care they can be suitable for very high-level organization) will have similar groups, which may or may not overlap with the top-level tags listed above.
I would love to see a GUI file browser designed with tags as a first-class concept. You might just call them "dynamic folders" - in any folder you can view a list of dynamic folders, generated by the tags in the current folder. This dynamic folder list could be adjusted from 1) only the top levels of the local tag hierarchy, down to N) all unique tags that are present in the current folder.
However, it’s a complete non-issue if the tags are automatically generated and updated.
I first noticed this in the iOS Photos app, which automatically generates collections such as “Weekend in Paris” and “Pictures of Bob”. The accuracy is good enough to be useful and can be improved automatically in future releases without requiring user interaction.