Cat. & Reference: Birds of a Feather
The 41 volumes of the Library of Congress classification schedules (i.e., the list of all the Library of Congress call numbers) take up about three feet of shelf space in my cubicle. In theory, I'm responsible for cataloging material on any topic in any volume, but in practice, the materials that cross my desk tend to cluster in a few areas (Canadian literature, Maine history and geography, etc.). However, I do occasionally work with material that is well outside my comfort zone, and since I don't have time to familiarize myself with every single page of every single classification volume, I have to use a lot of tricks to figure out where a book should be classed.
The simplest trick is a keyword search. So, if I have a book about Fabergé eggs that needs a call number, I can do a keyword search on the term "Fabergé eggs" in our catalog to find other books on the same topic to see where they're classed. (Verifying that a given call number is correct is much simpler than coming up with a call number from scratch. Plus, even if a call number from another book isn't quite what I'm looking for, it's likely to get me into the right general area of the schedules, and I can explore from there.)
Subject Heading Correlation
A second trick is look up the Library of Congress Subject Heading for a book (subject headings are kind of like standardized keywords) and see what number or numbers it corresponds to. The LC classification website has a neat feature where I can enter a subject heading and see what call number have been assigned to it by Library of Congress librarians. So, if I have a book with the subject heading "Bears," I get the following breakdown:
QL737.C27 - used 21 times (This number corresponds to the family Ursidae.)
QL795.B4 - 9 times ("Bears" under the broader heading of "Stories and anecdotes about animal behavior")
QL737.C2 - 4 times (General works about the order Carnivora)
PZ10.3 - 2 times (Children's stories about animals)
SK295 - 2 times ("Bears" under "Big game hunting")
This technique is useful when you have a very general subject heading or when a subject might be classed in more than one area. It's less useful when you have an obscure subject heading that doesn't correspond to any books in the Library of Congress, or when you don't have a subject heading at all, for whatever reasons.
This involves browsing from the most general classification terms to the most specific ones, and it's theoretically the standard way that catalogers are supposed to look for new class number, but in practice it's very complicated, because things are often hiding where you don't expect them. (Looking for the history of Alberta? It's not under Canada > History. Looking for books on Inuit linguistics? You'll need to pick the top heading "Hyperborean, Indian, and artificial languages," which is useful only if you know what "hyperborean" means.)
Of these three techniques, I'd say I probably use #2 most often and resort to the others only when I have to (or I go to #3 if I'm already pretty familiar with the schedule). However, there is one situation that I sometimes encounter which renders the first two techniques utterly useless and leaves me to rely on #3 or on my own knowledge of the world. I'll blog about that situation in a future post.