Dewey or don't we?

I took some of my mom's books as a donation to the school library today. I also looked at two listings on their shelves, to see if they were in good shape or if I could bring two more copies.

The fiction books are shelved alphabetically by author's last name -- this is standard -- for most authors. However, if you want to read a novel by John LeCarre, you have to look under David Cornwell, the author's real name. "Wait a minute," I wondered as I wandered the shelves. "Then how come I find books by Ed McBain not shelved under Evan Hunter (especially since there's an Evan Hunter book right there)? The librarian explained that she follows the Library of Congress standard.

One of the titles I sought today is a non-fiction book. When I looked it up in the (computerized) card catalog (available through the link above, if you're curious), it told me the book could be found at "500 Bryson". I stared at the screen, wondering what that meant. Yes, I has been that long since I'd seen the Dewey Decimal System. (NMSU uses the Library of Congress system.) Once I got my brain back on track, I found the book right away.

Now I guess I need to ask the librarian why she uses the Library of Congress system for fiction but the Dewey Decimal System for non-fiction.