Uniform Resource Identifier

The URI is defined in RFC 2396.
It looks like scheme:scheme-specific part. For example, the scheme part can be: data, file, ftp, httpd, gopher, mailto, news, telnet, wais, etc. The scheme-specific part usually looks like //authority/path?query
It can be further classified as either a location, a name, or both.
A Universal Resource Name (URN) is required to remain globally unique and persistent even when the resource ceases to exist or becomes unavailable. RFC 2141.
- urn:namespace:resource-name
- For example: urn:isbn:1234-98754-09
- Used by doi system.
A Universal Resource Locator (URL) identifies resources via a representation of their primary access mechanism. RFC 1738.
- protocol://username@host:port/path/file#fragment?query