The new GILFind catalog (in beta) allows you to cast your search net wide as you start and then narrow your search by choosing ‘facets’ in the results interface. (The Classic GIL catalog remains available for those who prefer it; see also the blog post introducing GILFind.)
A keyword search for “elephant” in all fields brings up 1084 results. If I’m interested in scientific books about elephants geared towards children, I can limit my search using several of the ‘facets’ in the left-hand column. First I’ll choose the call number Q, for Science books about elephants.
I’ve narrowed down to 130 results already. I can narrow further by choosing the Location as Aderhold Curriculum Materials Library – the campus library that collects children’s books.
I now have 28 books, all on the science of elephants (therefore not including, say, Babar) and all children’s or related to curricula. Each individual facet can be removed at any time, re-broadening the search without making me start all over again.