URL? URI? URN?

Hmm…., recently I was hear some different noun, about URI, URL and URN.

Normally I use to call it URL for all of the link address, but now I know that there has some different concepts for them, and after I search and browsing on Google, here is some exact define for it all.

I found some definition about it on either Wikipedia or some people blog,

URI (Uniform Resource Identifier):

It is a string of character used to identify a name independent of location or resource on the internet, thus a URI identifies a resource either by location, or a name, or both.
from Difference between URI, URL and URN

Thus URI can be including both URL and URN, or you can said URL and URN are part of URI, however not the other way around.

URL (Uniform Resource Locator):

It is a subset of the Uniform Resource Identifier (URI) that specifies where an identified resource is available and the mechanism for retrieving it.
from Difference between URI, URL and URN

It is colloquially termed a web address, is a reference to a resource that specifies its location on network, URL occur most commonly to reference web page(html), but are also used for file transfor(ftp://) or email(mailto://) for most, and many other application.
Definition from Wikipedia-URL

URN (Uniform Resource Name):

It is a Uniform Resource Identifier (URI) that uses the URN scheme, and does not imply availability of the identified resource.
from Difference between URI, URL and URN

It was conceived as persistent, location-independent, identifiers assigned within defined namespaces, typically by an authority responsible for the namespace, so that they are globally unique and persistent over long periods of time, even after the resource which they identify ceases to exist or becomes unavailable.[3]
Definition from Wikipedia-URN

For correspond some real world stuffs

URL

Something like a person address or something you can used for finding this people(website),

URN

Support to be a unique identify,
like personal ID or Name of a people.
More clearly is book ISBN(But is not a URL as it does not define where the book can be found)