URLs Explained
How do I refer to information on the Web?
When you send someone a postcard, all you need to know is their street
address. When you want to view a file on your hard drive, all you need to
know is its pathname. When you want to view information on the Web, you must
know its Uniform Resource Locator (URL). URLs provide a compact notation for
describing resources all over the Internet.
The Internet is not so mysterious
All interactions use a common protocol (TCP/IP) which requires a
hostname, service specification and some parameters.
For example:
A Uniform
Resource Locator (URL) is simply a compact way to represent the
same information:
Anything with slashes, colons, and dots is probably a URL
The general syntax of a URL is (more detail
is available):
URL ::= service://host/parameters
service ::= ftp, file, telnet, wais, gopher, news, http
host ::= Internet address [ : port ]
| user [ . passwd ] @ Internet address [ : port ]
| localhost (empty hostname implies localhost)
parameters can be ftp://host/filename
| file://host/filename
| telnet://host/
| wais://host/keyword [ ?keyword ... ]
| gopher://host/menu_item [ / menu_item ... ]
| news:newsgroup
| http://host/filename
| http://host/cgi-bin/program/params
| http://host/formname [ ? param ... ]
For the gory details check the TCP RFC's, /etc/services file,
and Bennet Yee's faucet
program from his
gms.tar.Z software. You can play with these protocols directly
(outside of mosaic) using the telnet host service command
on a unix system.
mwm@cs.cmu.edu
