RequestA Request is the second step of the four-part HTTP (Hypertext Transfer Protocol) connection. HTTP is the protocol used for accessing files on the World Wide Web.
The request is part of the process of data transfer that is normally not apparent to the user. The user only has to click on a hypertext link, and the interaction between the client and server (as specified by the protocol) does the rest. However, it is a good idea to understand this interaction between the client and server, as it is a model for different protocols, some of which require more active participation by the user.
HTTP was designed to be a quick and efficient means of data delivery. In order to achieve this goal, the scientists at CERN established a client/server relationship that would function by allowing only one transmission per connection. During the request stage of the connection, the client sends a message to the server asking for a certain type of response. The type of request depends on the language used by the client when requesting information; the client must specify the method of transaction. GET is a commonly used method; it specifies that the server should retrieve a URL (Uniform Resource Locator). URLs are the addresses given to hypertext documents.
The request also contains information about the capabilities of the client. The client in the HTTP client/server relationship is the browser. Since browsers differ in the methods they support, the server must know whether certain requests can be processed completely. For example, Netscape for Macintosh supports the method called Mail To, which allows users to send e- mail to linked addresses by clicking on the provided hypertext link. However, Mosaic for Macintosh does not support Mail To. When a user clicks on the same link when viewing a document through Mosaic, the server will send back a response informing the user that the request could not be completed.