domain name

DOMAIN
Domain
Root
Sub domainA domain is a subtree of the domain name space. The name of the domain is the domain name of the node at the top of the subtree. Note that a domain may itself be divided into domains (or subdomains).



Zone is a contiguous part of the entire tree. It a server accepts responsibility for a domain and does not divide the domain into smaller domains, the domain and the zone refer to the same thing.
WWW and HTTP
The WWW project was initiated by CERN (European Laboratory for particle Physics).
Client
Request t
Site/server
Wed page
Response The WWW today is a distributed client/server service, in which a client using a browser can access a service using a server.




A browser is a program that is designed to fetch web documents.
Each browser usually contains of three parts: a controller, client protocol, and interpreters.
The controller receives input from the keyboard or the mouse and uses the client programs to access the document. After the document has been accessed, the controller uses one of the interpreters to display the document pm the screen. The client protocol can be one of the protocols ‘FTP, HTTP etc. The interpreter can be HTML, Java, or Java script, depending on the type of document.
Server always store requested files in a cache in memory; memory is faster to access than disk.
Uniform Resource Locator (URL) is a standard for specifying any kind of information on the internet. The URL defines four things; protocol, host computer, port, and parth.
URL
Protocol: //Host: Port/Path
The protocol is the client/saver program used to retrieve the document eg FTP/HTTP. The host is the computer on which the information is located.
The URL can optionally contain the port number of the server.
Path is the path name of the file where the information is located.
Cookies are used by server to know old client and to restrict access to unauthorized client.
The site that restricts access to registered clients only sends of cookie to the client when the client registers for the first time. For any repeated access, only those clients that send the appropriate cookie are allowed.
Note that the contents of the cookie are never read by the browser or disclosed to the user. It is a cookie made by the server and eaten by the server.