We found an entertaining illustration comparing the contruction of a number for one particular book in the Dewey Decimal System (familiar to you as public library users; most US public libraries use it); in the Library of Congress system; and in the Universal Decimal Classification. Mostly we don't think of our catalog as embodying a philosophy of the classification of knowledge. It's a finding aid: what do we have, and where is it? And yet, unless they're on a mission for a known item, what public library users often want is to be pointed to a shelf where a number of items on their topic can be found. Where it is, in our library, is mapped out by Dewey's 22-times-revised system of knowledge. In most academic libraries, by Library of Congress' system. Imagine the dismay of those NYPL research users who know just where things have sat in the Main Reading Room for decades, when everything suddenly moves.