url -- Uniform Resource Locator
uri -- Uniform Resource Identifier
urn-- Uniform Resource Name
The difference between URL, URI & URN is subtle.
URL(Uniform Resource Locator) is the term used to identify an Internet resource, and can be specified in a single line of text. It refers to the subset of URIs that, in addition to identifying a resource, provide a means of locating the resource by describing ites primary access mechanism.[http://www.ietf.org/rfc/rfc1738.txt]
URI(Uniform Resource Identifier) provides a simple and extensible means for identifying a resource. A Universal Resource Identifier (URI) is a member of this universal set of names in registered name spaces and addresses referring to registered protocols or name spaces. [http://www.ietf.org/rfc/rfc1630.txt, http://www.ietf.org/rfc/rfc3986.txt]
URN(Uniform Resource Name)is the term used to identify an Internet resource, without the use of a scheme, and can be specified in a single lineof text[http://www.ietf.org/rfc/rfc1737.txt]
Such as,
URI: http://www.example.com/index.html#fragment1
URL: http://www.example.com/index.html
URN: www.example.com/index.html#fragment1
Reference:
1.http://www.w3.org/Addressing/
2.http://www.ietf.org/rfc/rfc1738.txt
3.http://www.ietf.org/rfc/rfc1630.txt
4.http://www.ietf.org/rfc/rfc3986.txt
5.http://www.ietf.org/rfc/rfc1737.txt
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