A Uniform Resource Locator or URL is a "networked extension" of the standard "filename" concept. It can also be thought of as a fancy name for an address. Note: The "Uniform" in URL is also referred to as "Universal."
Each file (i.e. resource) on the Internet has a unique URL that identifies its location.
URL Related Quotes
"URLs are the 800 numbers of the 1990's." -- annoymous
"It is the most fundamental innovation of the Web." -- Weaving the Web Tim Berners-Lee.
The basic URL contains the following components:
- server name
- path and file name
Optionally, the server name may be followed by a colon and an integer number. If it is, then the number is a port identifier. Frequently used protocols have "fixed" or " common" port identifiers (e.g.
HTTPuses port number 80). Example:http://cszero.sc.maricopa.edu:80/index.html
The following is a table of common port numbers.FTP........21 telnet........23 SMTP.......25 gopher........70 HTTP.......80 NTTP..........119 SSH........22
When specifying a URL, the protocol is typically followed by a colon and two forward slashes.
newsare exceptions; these use a single colon.
List of example URLs.http://azlitter.org/notes/carts/index.html protocol -- http server name -- azlitter.org (domain name) path -- notes/carts file name -- index.html http://deru.com/gdt This URL points to a user-supported directory that contains resources fetchable via the WWW (i.e. http). A user having the account name gdt exists on the deru.com server. http://deru.com/gdt/images/CoolGuy.gif This URL points to a file named CoolGuy.gif that is stored on a server having the domain name deru.com . On the deru.com server in the user's public_html directory is a directory name images and the CoolGuy.gif file is stored in that directory. http://deru.com/gdt/csc185/assignments/ A URL with a trailing forward slash and no file name points to the default file in the last directory named. The default file on many servers is index.html . If no default file exists, then either a directory listing or error webpage are returned [behavior depends on how the webserver is configured].
Table demonstrating different type of URLs.
FTP ftp://ftp.fh-wolfenbuettel.de Usenet news:alt.binaries.sounds.mp3.1990s mailto:firstname.lastname@example.org Gopher gopher://gopher.tc.umn.edu WWW http://KeepTheInternetFun.org/ Telnet telnet://nyx.net File access locally stored file
URLs can be either absolute or relative. Relative URLs are used from within webpages.
Domain names are not case-sensitive; in other words,
FOO.comis the same as
foo.comwhich is the same as
Foo.Com. The rest of the URL beyond the domain name is case-sensitive.
More on URLs
If you want to become a Guru on URLs, then the following websites should provide all the information you need.NCSA.UIUC.edu:: A Beginner's Guide to URLs
W3.org:: Naming and Addressing: URIs, URLs, ...
Ohio-State.edu:: RFC 1738: Uniform Resource Locators [published December 1994]
Last Modified: Saturday, 05-Jan-2013 11:20:35 MST