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.
URL's represent hypermedia links and links to network services within HTML documents. It is possible to represent nearly any file or service on the Internet with a URL.
All interactions use a common protocol (TCP/IP) which requires a hostname, service specification and some parameters. For example:
ftp ftp.telstra.com.au service, host cd pub/docs/security/ parameters get README
A Uniform Resource Locator (URL) is simply a compact way to represent the same information:
ftp://ftp.telstra.com.au/pub/docs/security/README http://www.telstra.com.au/ telnet://downwind.sprl.umich.edu:3000/ file://explorer.arc.nasa.gov/pub/SPACE/GIF/gaspra.gif wais://gourd.srv.cs.cmu.edu:6000/bovik? gopher://olt.et.tudelft.nl:1251/11/space news:comp.infosystems.www
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 ... ]
The first part of the URL (before the two slashes) specifies the method of access. The second is typically the address of the computer the data or service is located. Further parts may specify the names of files or the text to search for in a database. A URL is always a single unbroken line with no spaces.
Most Web browsers allow the user to specify a URL and connect to that document or service. When selecting hypertext in an HTML document, the user is actually sending a request to open a URL. In this way, hyperlinks can be made not only to other texts and media, but also to other network services. Web browsers are not simply Web clients, but are also full-featured FTP, Gopher, and telnet clients.
Electronic Commerce on the Internet - WWW (World Wide Web) - the "Glossy Brochure"
Rodney
Campbell [Rodney.Campbell@Telstra.com.au]
(c)
Copyright 1995 Telstra Corporation.
Last modified: Tue May 16 20:05:47 1995