Kendall Grant Clark has been getting into the nitty-gritty of doing a librarian's work with xml and rdf. His latest article is part of his Hacking the Library series at XML.com.
Our isbn2lccn tool will read its command line arguments, one of which will be a required ISBN. It will then make some REST web service calls to either the Library of Congress or the British Library; in some cases it may also make calls to Amazon or to xISBN. Source.