>>> [log in to unmask] 2004-11-30 10:31:10 >>> > Well, DOI. And what of isbns or lccns? ISBN can have too much granularity from the standpoint of reference management, e.g. when there are hardcover and softcover printings of the same edition of a book with different ISBNs. And then there are books, such as some Springer-Verlag titles, with two ISBNs for one printing.