What is the difference between URI, URL and URN?
What's the difference between an URI, URL and URN? I have read a lot of sites (even Wikipedia) but I don't understand it.
URI: http://www.foo.com/bar.html
URL: http://www.foo.com/bar.html
URN: bar.html
Is this correct?
Answer
Uniform Resource Identifier (URI) is a string of characters used to identify a name or a resource on the Internet
A URI identifies a resource either by location, or a name, or both. A URI has two specializations known as URL and URN.
A Uniform Resource Locator (URL) is a subset of the Uniform Resource Identifier (URI) that specifies where an identified resource is available and the mechanism for retrieving it. A URL defines how the resource can be obtained. It does not have to be HTTP URL (http://), a URL can also be (ftp://) or (smb://).
A Uniform Resource Name (URN) is a Uniform Resource Identifier (URI) that uses the URN scheme, and does not imply availability of the identified resource. Both URNs (names) and URLs (locators) are URIs, and a particular URI may be both a name and a locator at the same time.
The URNs are part of a larger Internet information architecture which is composed of URNs, URCs and URLs.
bar.html is not a URN. A URN is similar to a person's name, while a URL is like a street address. The URN defines something's identity, while the URL provides a location. Essentially, "what" vs. "where". A URN has to be of this form <URN> ::= "urn:" <NID> ":" <NSS> where <NID> is the Namespace Identifier, and <NSS> is the Namespace Specific String.
To put it differently:
- A URL is a URI that identifies a resource and also provides the means of locating the resource by describing the way to access it
- A URL is a URI
- A URI is not necessarily a URL
I'd say the only thing left to make it 100% clear would be to have an example of an URI that is not an URL. We can use the examples in the RFC3986:
URL: ftp://ftp.is.co.za/rfc/rfc1808.txt
URL: http://www.ietf.org/rfc/rfc2396.txt
URL: ldap://[2001:db8::7]/c=GB?objectClass?one
URL: mailto:[email protected]
URL: news:comp.infosystems.www.servers.unix
URL: telnet://192.0.2.16:80/
URN (not URL): urn:oasis:names:specification:docbook:dtd:xml:4.1.2
URN (not URL): tel:+1-816-555-1212 (?)
Also check this out - https://quintupledev.wordpress.com/2016/02/29/difference-between-uri-url-and-urn/