When is a persistent identifier not persistent? Or an identifier?

Abstract

• Ever wondered what that bar code on the back of every book is? It’s an ISBN: an International Standard Book Number. Every modern book published has an ISBN, which uniquely identifies that book, and anyone publishing a book can get an ISBN for it whether an individual or a huge publishing house. It’s a little more complex than that in practice but generally speaking it’s 1 book, 1 ISBN. Right? Right.