HTTP Protocol - URI

Uniform Resource Identifier (URI): compact sequence of characters that identifies an abstract or physical resource.

Syntax:

　　URI = scheme ":" hier-part [ "?" query ] [ "#" fragment ]

　　hier-part = "//" authority path-abempty
                  / path-absolute
                  / path-rootless
                  / path-empty
example:

　　foo://example.com:8042/over/there?name=ferret#nose
   \_/   \______________/\_________/ \_________/ \__/
    |           |            |            |        |
 scheme     authority       path        query   fragment
    |   _____________________|__
   / \ /                        \
   urn:example:animal:ferret:nose

"Uniform Resource Locator" (URL):
　  Refers to the subset of URIs, in addition to identifying a resource, provide a means of locating the resource by describing its primary access mechanism.

"Uniform Resource Name"  (URN):
　　Intended to serve as persistent,location-independent, resource identifiers.
　　All URNs have the following syntax (phrases enclosed in quotes are

   REQUIRED):

                     <URN> ::= "urn:" <NID> ":" <NSS>

   where <NID> is the Namespace Identifier, and <NSS> is the Namespace Specific String.

Refer below:
https://tools.ietf.org/html/rfc3986
https://tools.ietf.org/html/rfc2141
https://en.wikipedia.org/wiki/Uniform_Resource_Identifier