What kind of reference source should I consult in order to find out whether there is a librarian character in a writer's novel, say Barbara Pym or someone else's?
This is a school assignment. I am learning how to use reference source, obviously I have a long way to go.
In order to find fiction about a given theme, consult any library catalogue you wish. In most library catalogues nowadays, the titles have been provided with ample description about the contents of the work in question. This means that you can choose your keywords fairly freely. Only bear in mind that such searches can never give a 100% result, due to the fact that it is impossible to catalogue every single aspect of e.g. a novel.
So, choose any library catalogue. You do not tell why you are sending your question to the Finnish "Ask a librarian" service, but assuming that you are especially interested in Finnish sources, you have to use keywords in Finnish in your searches. Choose. e.g. the HelMet catalogue ( http://www.helmet.fi/screens/opacmenu.html ). There, choose Keyword search. Type the Finnish keywords "kirjastonhoitajat" and "kaunokirjallisuus" (librarians and fiction), and you will find 15 titles.
In case you choose a catalogue of any English-speaking library, you can, of course, use the corresponding keywords in English.
One of the largest literature databases is WorldCat (OCLC First Search). Unfortunately, you cannot use it freely over the Internet, but you will probably find an access to it at your library. Another large database is the Library of Congress Online Catalog ( http://catalog.loc.gov/ ).
In any on these catalogues, I did not find novels by Barbara Pym with librarians as characters, but lots of other fiction dealing with librarians and librarianship.
In many books, there is nowadays a description of the contents of the book (usually behind the title page). Often, this description is taken from the Library of Congress Catalogue. These descriptions can, of course, be also used as reference sources, but in order to find the right books, you have to use a library catalogue.
To get a better idea of the method, I advise you to go to the nearest library and ask there. I am sure the staff will be happy to help you in your quest.