Right. Turns out my use of 'URL' everywhere in grandparent comment is a misnomer then. Should've used URN or URI.
I'm not quite sure if URN is exactly right for the hash thing either, given that it both fails to unify things which humans would probably assign the same URN to, such as two image files of the same picture using different encodings, and it has the theoretical chance of assigning the same hash to two entirely different things.
* Global uniqueness: The same URN will never be assigned to two different resources. ((the encoding would be part of the URN))
* Independence: It is solely the responsibility of a name issuing authority to determine the conditions under which it will issue a name. ((a URN wouldn't necessarily be a hash of the resource in question))
The second point makes it pretty clear that the assignment of URN's would be done by some authoritative parties, which makes sense if you think that in their initial view URN's would have been useful in linking citations, references; for research papers. Just that the Internet has far time ago branched from that scope.
This (non-canonical) interpretation of the UR<x> schemata works for me (in terms of dealing with ambiguity of the canonical specification):
Names: universally unique and fully scoping the life-cycle of the (logical) object. 1:1.
Identifiers: unique in context of an authority with a life-cycle that is maximally (but not necessarily) bounded by the life-cycle of the named entity (and of course, the authority that assigns it). e.g. http://www.ssa.gov/history/ssn/geocard.html is the authority that issues SSN identifiers. An entity can potentially have multiple such identifiers. 1:N
Locations: The location of an image or representation of the entity. 1:N (e.g. CDNs)
