What's different between URI, request-URI and URL?

Question

I'm learning Web tech and teacher cannot give me a satisfactory explanation. I'd like to give a few example, please help me to point out am I right.

• I know URL is a subset of URI
• http://www.example.org:56789/a/b/c.txt?t=win&s=chess#para5 is a URL and also a URI
• every address we type in browsers can be called URL
• http://www.example.org:56789/ is also a URI
• the part: a/b/c.txt?t=win&s=chess is request-URI
• the part: para5 does not belong to the request-URI is just a fragment

Answer 1

The URI standard is STD 66, which currently maps to RFC 3986.

URI vs. URL

Section 1.1.3 describes the difference between URIs and URLs (and URNs).

Components

Section 3 describes the components a URI can have.

For the URI http://www.example.org:56789/a/b/c.txt?t=win&s=chess#para5 these would be:

• Scheme: http

• Authority: www.example.org:56789

• User Information: not present

• Host: www.example.org

• Port: 56789

• Path: /a/b/c.txt

• Query: t=win&s=chess

• Fragment: para5

request-URI

The term "request-URI" is not defined or even used in STD 66 / RFC 3986.

Answer 2

The term "Request-URI" is defined by the HTTP standard (RFC 2616, §5.1.2), and refers to the URL as it is given in the actual HTTP request.

In normal HTTP requests, the URL scheme and host have already been handled by the time the request is sent (and the URL fragment does not exist at the HTTP protocol level at all), meaning the Request-URI is a path-absolute-URL string, possibly followed by ? and a URL-query string.

That is to say, this part of the complete URL:

https://example.org/path/to/file?param=42#fragment
                   ^^^^^^^^^^^^^^^^^^^^^^

Note that it includes the leading /.

Exceptions to this include:

• For e.g. the OPTIONS HTTP method, the Request-URI may simply be *.
• When the HTTP server is acting as a proxy, the Request-URI may be a complete absolute-URL string (still excluding the fragment).
• Other, more elaborate/non-standard things.