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URL General Syntax
(Page 2 of 4)
Common Internet Scheme Syntax
In theory, each scheme may use a
completely different syntax entirely for the <scheme-specific-part>.
However, many of these schemes share a common syntax for this part,
by virtue of the similarities in how they refer to internetwork devices
and resources on those devices. For example, both HTTP and FTP are used
to point to specific TCP/IP devices using a DNS name or IP address,
and then access resources stored in a hierarchical directory structure.
It makes sense that their URLs would be at least somewhat similar.
The most general form of this common
Internet scheme syntax is as follows:
The elements of this syntax are as
- <scheme>: The URL scheme, as described
- <user> and <password>: Authentication
information for schemes requiring a login, in the form of a user name
- <host>: An Internet host, usually
specified either as a fully
qualified DNS domain name, or an IP address
in dotted-decimal notation.
- <port>: A TCP
or UDP port number to use when invoking
the protocol appropriate to the scheme.
- <url-path>: A resource location
path. This is usually a full directory path expressing the sequence
of directories to be traversed from the root directory to the place
where the resource is located, and then the resource's name. For example,
if on a device there is a directory called project1 and
within it a subdirectory called memos containing a text
file called June11th-minutes.txt, the URL path project1/memos/June11th-minutes.txt
would refer to that resource.
Note that the slash before the <url-path> is required, and while
it is technically not considered part of the path, it serves the purpose
of acting like the slash denoting the root directory in
many file systems. Also, the <url-path> may end in a slash, which
means that the path refers specifically to a directory. However, this
is often not required, as the server will treat the URL as a directory
reference by context when needed. A path may also refer to a virtual
file, program or resource other than a normal file.
- <params>: Scheme-specific parameters
included to control how the scheme is used to access the resource. Each
parameter is generally of the form <parameter>=<value>,
with each parameter specification separated from the next using a semi-colon.
- <query>: An optional query or other
information to be passed to the server when the resource is accessed.
- <fragment>: Identifies a particular
place within a resource that the user of the URL is interested in.
illustrates this common syntax and its elements using an example HTTP
Figure 287: Example Uniform Resource Locator (URL)
This diagram shows a sample URL that includes almost all of the possible elements in the general scheme syntax, each of them highlighted using snazzy rainbow-colored boxes. J This URL identifies a Web (HTTP) resource that must be accessed using a particular password at the site www.mysite.org using port 8080. The resource in this case is a PHP program in the sites cgi-bin directory that causes a particular page of photographs to be displayed. The <fragment> specifier will cause the picture Reception07 on the retrieved page of wedding photos to be displayed to the user.
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The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
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