The Universal Standard Book Number (openusbn.org)

I feel like normalization would be a nightmare. Consider all the mistranscriptions, OCR errors, and different names in the libraries (case, parentheticals, etc).

If we assume there's no reliable way to define a book, maybe locally sensitive hashing could help find probably same books.

The idea is pretty cool though.

I would believe there is a nontrivial amount of books by the same author published in the same year with the same title either in different formats, different languages, and/or by different publishers.