it’s often stated that hierarchical categories are too limited and that a tagging system is better. putting aside arguments about what a “category” represents taxonomically and how it differs from a “tag” (e.g. “grouping vs describing”, “general vs specific”, etc), there ought to be more flexibility in tags and tagging in order to make it a worthwhile mental model shift vs. categories.

i generally agree that a strict hierarchy is not the best, even if it is sometimes (often?) good (enough?). the classic issue is with e.g. folders in a filesystem, a folder can have only one parent. sure you can set up symlinks but the one-parent rule is an issue that needs to be worked around.

the shift from categories to tags “solves” this “one-parent rule” issue. (but again, you could just as easily say that an item can belong to multiple categories; etc etc. we leave this argument out because it is too similar to the taxonomic argument above)

now we have to come up with improvements to the tagging system. below are some mechanisms

hierarchical tags [link]

x.y.z implies x.y and also implies x. it might also imply y (unclear)

cons: it replicates the one-parent rule and its issues, and it’s unclear how inheritance works. also what do you use as the separator between hierarchy layers? a dot? a slash?

prior art:

• also called “nested tags” by obsidian

taggable tags [link]

just like modern OOP principles tell you to favor composition over inheritance, we favor taggable tags over hierarchical tags.

z is tagged with x and y; therefore, anything tagged with z implies x and implies y

example: tagging a character from a series implies tagging the series. #gaimon_(one_piece) is your classic booru style binary tag that is too basic. what you want is to imply that #one_piece tag without actually having to tag it yourself. but you also want to imply many other tags: #green_hair, #treasure_chest, #afro, and so on. you don’t want to add these tags yourself every single time.

prior art:

• hydrus network calls this “tag parents”. it works off of semantic subsets and supersets.

tag aliases [link]

z implies zee (and vice versa); z implies zed (and vice versa)

prior art:

• also called “tag siblings” by hydrus network. allows you to set up equivalence between semantic concepts.

you can chain these together transitively or keep them flat, but it is generally a good idea to mark one of the ends as “canonical” implying it overrides the other. say you want to have a common misspelling be overridden by the correct spelling