Now locationless identifiers would work fine regarding persistence, but the problem is scalable resolution. Both are right, in different ways, because the multiple things are about the same thing. If they are not about the same thing, then we have lost the global context. This makes it clearer why people are so keen on mapping URNs to metadata or to a list of URLs. I want URNs to be primarily associated with the thing all the metadata are about, and if instead you want some metadata, then you ask explicitly for it by a different kind of request.
Replication is essential.
Perhaps we should just hide behind the services associated with resources, which are identified by either URLs or URNs. If you do a HEAD on a URN, you get some metadata for it. So my agreement at the beginning that a URN can be associated with many things, though correct, is misleading regarding this way of thinking about the primary association and other associations. This is exactly the point. A 'unique key' doesn't contain a pointer at all.