1.5. URLS AND DOMAIN NAMES

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http://www.brandeis.edu:80

http://www.brandeis.edu:80/index.html

http://www.brandeis.edu:80/go/index.php?go=cosi

http://129.64.2.3/~tim

http://jscheme.cs.brandeis.edu:8080

ftp://ftp.cc.gatech.edu/pub/linux/

The simplest form of a URL is just:

http://DOMAINNAME

where  http  , and  DOMAINNAME  .

The general form for a URL is

PROTOCOL://DOMAINNAME:PORT/PATH/FILE.EXT#P?N=V&N2=V2 ...

Lets break this apart.

   PROTOCOL  specifies the protocol that the web browser must use to

communicate with the web server. There are many other protocols besides

http. The most common is  ftp  which is the  file transfer protocol.  The

 mailto:  protocol is also common and is used to allow the user to send

email from a browser.

  DOMAINNAME is the symbolic name of the web server. All web servers

have a unique IP address (as described above). The conversion between

domain names and IP addresses is performed using special servers on the

net called  Domain Name Servers.  These servers accept domain names

and send back the corresponding IP address. They are the equivalent of

the  411  service on phone networks and every browser must have the

address of at least one Domain Name Server if it is going to use domain

names. You can use IP addresses directly in the URL instead of a domain

name, but this is rarely done as IP addresses can be hard to remember.

   PORT  is a number between 0 and 65535 which specifes the port used

by the server, the default value is 80 for http protocols

   PATH  specifies the location of the file on the server

   FILE.EXT  is the name of the file to be returned

   #POS  specifies a location in the file. POSITION is a symbolic name

(containing no blank spaces). The browser will scroll the window down to

that position when first viewing the file.

   ?N=V&...  This is a mechanism for passing values to the server which

it can use to generate the web page it will send back to you. You often

seen this kind of an address after filling out a search form for a search

engine. When you bookmark this page and return to it, the URL contains

a precise description of everything you entered on the form.

These more complex URLs will be come easier to understand after we have

discussed servlets in a later chapter.