Controlled Vocabulary vs Natural Language
I just finished Libby Bray's witty, dark, deep Going Bovine and added it to my Shlefari. "How shall I tag it," I asked myself (yes, I not only talk to myself, I also use words like "shall" - deal with it). I never remember if I prefer "urban fantasy" or "alt fantasy"; should I choose "death and dying" from the suggested tags?; "road trip" goes without saying.
Then, for whatever reason, I took a look at the catalog record: "automobile travel - fiction" and "Bovine spongiform encephalopathy - fiction" and "dwarfs - fiction" -- seriously? I never considered that buddy Gonzo's dwarfism was part of the "aboutness" of the book. And why on earth isn't "road trip" a proper subject heading?
One thing subject headings (controlled vocabulary) and tags (natural language) can do is get us back to the book, even if it word or scene in our mind isn't a critical part of the book's aboutness. Imagine a patron saying, My friend told me about this book about a guy with mad cow disease who goes on a road trip with this other guy and they pick up a talking yard gnome. You'd want to try key words like "road trip" and "yard gnome" in your search. In library school, we certainly didn't memorize massive lists of subject headings, but we know how they work. Through practice, we learn to type things like "theater vocational guidance" to replace the patron's "get theater jobs" and, it seems, "automobile travel" for "road trips."