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Universal Resource Locators

a Universal Resource Locator (URL) tells you were you can find a World Wide Web page. Each URL is constructed as:



The protocol determines in what way the information has to be obtained. Valid protocols are e.g.

Hyper Text Transfer Protocol. The protocol to get Web pages.
file or ftp
The document referred to will be downloaded as a normal file.
Starts a telnet session to host.domain. The /path part is empty.
A link to a Usenet newsgroup. The host plus domain part determine the news-server (for instance news.surfnet.nl) and the path part is de newsgroup.
In this case the remaninder of the URL forms a e-mail address to which a mail will be sent.

Host and Domain

The fully qualified name of the computer serving the document. It is common practice to define an alias for computers operating as www servers. This has two advantages. Firstly one can use an easy to remember alais, for instance wwww, and secondly the service can be easily moved to an other computer by letting the alias point to another computer.


WWW traffic across the Internet uses a set of rules commonly called a protocol: Internet Protocol or simply IP. This protocol also defines how the different connection types (ftp, telnet, http, smtp, nntp, etc.) can be recognized. This is done using a number, the so called port number. The default port for HTTP-traffic is 80. The :port part of the URL may be left out when the WWW service runs on this port number.


Depending on the protocol this is the path to a document or the name of a newsgroup


  • http://www.science.ru.nl/cncz/: The homepage of C&CZ.
  • ftp://ftp.science.ru.nl/ The ftp-service of the Faculty of Sciences.
  • http://opc.ubn.ru.nl The online Public Catalogue of the University Library.
  • mailto: A mail to the person acting as Postmaster at C&CZ, typically used to send requests or problem reports