Tagging is common in contemporary information systems, but Tags are an ineffective association structure. One more effective historical antecedent is the index in publishing.
Indexes don’t strive to include every relevant page number for a given term; instead, it includes a handful of top references. By contrast, the listing of items with a particular tag often becomes quite unwieldy.
Indexes can also include other editorial content. For instance, an entry might note “See also: …”
Both index entries and sophisticated tagging systems can be hierarchical.
Luhmann kept his index cards tightly curated. They were meant mostly as a jumping-off point: the inter-note associations are more important.
Ahrens, S. (2017). How to Take Smart Notes: One Simple Technique to Boost Writing, Learning and Thinking – for Students, Academics and Nonfiction Book Writers.
In the Zettelkasten, keywords can easily be added to a note like tags and will then show up in the index. They should be chosen carefully and sparsely. Luhmann would add the number of one or two (rarely more) notes next to a keyword in the index (Schmidt 2013, 171).
Because it should not be used as an archive, where we just take out what we put in, but as a system to think with, the references between the notes are much more important than the references from the index to a single note.
Only tags that are specific to the objects I use and mention in a note are worthy: To take precise actions over a long distance I need a sniper rifle and not a shotgun.
Searching on a topic in your archive is like firing a shotgun into the woods and hoping that there will be food on the table somehow. I need a sniper rifle, night vision goggles, and infrared satellite pictures as if I have cheated the hell out of Counter-Strike. (I never did by the way.) There is some sneaky, precious game out there.