Sorry, bad analogy. Call numbers for books do change but not often and the holdings records ("the" catalog) behind the scenes reflect all changes. While ISBNs are cataloged, they aren't used as the main identifier. Whatever new scheme might come along will incorporate the past records. This is a very mature field though and one of the reasons I wanted to work for a library rather than elsewhere as the work involves keeping the past accessible while adding access to the future. Librarians have been -mostly- quietly at the forefront of copyright issues, data retention and access, format changes, and cataloging the difficult to catalog. Several of our librarians are working with university archives to add their content to the library catalog as fast as accuracy will permit. Electronic formats are a huge issue currently. URLs that go away are a bane of librarians lives. Cataloging a literary work on a site that goes away due to hosting costs may forever cost the world some fine or important literature. The history of Iran may miss a huge chapter due to most of recent events being coordinated on Twitter. I'll butt back out now. Don Bosman -----Original Message----- From: MSU Network Administrators Group [mailto:[log in to unmask]] On Behalf Of David McFarlane Sent: Thursday, September 03, 2009 11:44 AM To: [log in to unmask] Subject: Re: [MSUNAG] Digital preservation: a sad link rot story from MSU Web space Rich, And why should I expect URLs to persist? Shelf numbers for books do in fact change -- as time progress, libraries may change from, e.g., the Dewey Decimal system to Library of Congress numbers to ISBNs, and who is to say what further scheme will come along to supplant those?