Why is URN one of more popular formats used to uniquely identify the resource?

Question

I somewhat understand that URNs are used to provide unique and location independent name for the resource. Yet I fail to see their usefulness and how exactly they work:

a) In order for URN to really be unique, there would have to be some central authority (similar to authority for domain names) where we could register URNs and that way ensure they are unique. Since there isn’t any such authority, how else do we make sure that our URNs are unique? And if we can’t. then what’s the point of having them?

b) Also,I don’t understand the reasoning behind URNs having the format urn:NID:NSS. What makes this format more efficient/logical than for example urn:NID:NID1:NSS?

c) And finally, how can URN help us locate a resource on the internet?

EDIT:

I'm not sure what you mean. NID is the Namespace Identifier and NSS is the Namespace Specific String Are you proposing a system of sub-namespaces?

I’m just trying to make sense of why the format URN uses is “superb” to other formats, such as urn:NID:NID1:NSS

Answer 1

a) In order for URN to really be unique, there would have to be some central authority (similar to authority for domain names) where we could register URNs and that way ensure they are unique. Since there isn’t any such authority, how else do we make sure that our URNs are unique? And if we can’t. then what’s the point of having them?

An ISBN is used an a URN, and is managed by an agency.

b) Also,I don’t understand the reasoning behind URNs having the format urn:NID:NSS. What makes this format more efficient/logical than for example urn:NID:NID1:NSS?

I'm not sure what you mean. NID is the Namespace Identifier and NSS is the Namespace Specific String Are you proposing a system of sub-namespaces?

c) And finally, how can URN help us locate a resource on the internet?

A URN (Uniform Resource Name) doesn't help you locate something on the Internet. A URL (Uniform Resource Locator) does.

Also see What is the difference between URI and URL?

Answer 2

a) In order for URN to really be unique, there would have to be some central authority... Since there isn’t any such authority, how else do we make sure that our URNs are unique?

There is a central authority to register namespaces (the NID part), and each namespace is responsible for ensuring uniqueness.

b) Also, I don’t understand the reasoning behind URNs having the format urn:NID:NSS. What makes this format more efficient/logical than for example urn:NID:NID1:NSS?

The "urn:NID:NSS" description states the interpretation of NSS depends on the value of NID. For example, if NID is "isbn", then we know to interpret the NSS as an ISBN number, as in "urn:isbn:0451450523".

The NSS part can contain colons, so "urn:example:other:more" is valid syntax. (However, it's an invalid URN, because the "example" namespace isn't registered.) For example, given "urn:mpeg:mpeg7:schema:2001", the NSS part is "mpeg7:schema:2001" and we interpret that according to the rules for the "mpeg" namespace.

Had "urn:NID:NID1:NSS" been required, it would have been redundant (some namespaces don't need a nested NID1) and superfluous (the authority for a namespace can already divide the NSS part up, as in the above mpeg example).

c) And finally, how can URN help us locate a resource on the internet?

URNs are not about location, that's a URL.