If there is one technology that caught up literally overnight and has affected more users than any others, it is the web. The world wide web (WWW) is the set of all web sites and the documents they can provide to clients (Users). Visual Basic 6 has evolved to help the programmers to build web applications. There are two different types of web applications – Dynamic HTML (DHTML) applications and Microsoft Internet Information server (IIS) applications.
Internet concepts
This section briefs essential internet concepts as follows
Internet
The internet is a global network of computers that communicate using a common language. It is similar to the international telephone system – no one owns or controls the whole thing, but it is connected in a way that makes it work like one big network. The internet uses a common protocol to communicate TCP/IP (Transmission Control Protocol/ Internet protocol). TCP/IP is a simple protocol because it had to be implemented consistently on all computers and operating systems. Indeed, TCP/IP is a truly universal protocol, it’s there when you need it and allows your computer to connect to any other computer on the Internet.
Each computer on the Internet has a unique address, for example, 193.25.84.100. Each number is a value in the range 0 through 255, which means the internet have more than 256*256*256*256, or approximately 4,000,000,000 computers. To accommodate a large number of users, internet service provider use a pool of addresses (since not all users connect at once, 256 addresses may accommodate 100users or more. It would be nice if we all had a unique IP address, like an e-mail address, but this is not possible, if we did, we could build wide area networks that span the globe easily. However, every time you connect to your internet service provider you get a different IP address.
Intranet
Unlike internet, which is a global network, it is a private network, but it uses the internet communication standards and tools to provide information to the restricted users. For example, a company may setup a web site that is accessible only to its employees who are geographically separated. On an intranet. You can exploit the web model to simple operations, without the security issues you face on the Internet or the limitation imposed by connection computers with modems.
An intranet is also a network of computers operating on the TCP/IP protocol, but it is not global. Intranets are restricted to the users of a corporation. A university, or some other organization, and they are not accessible by the outside world. Unlike the world wide web, intranets don’t have more than one server. This machine supplies all the documents required by the client. Many corporation use intranets to provide information to their employee, and they run another web site for external users. The reason for building corporate intranets to exploit the technology. They made the web so popular. So the main characteristic of a corporate intranet is not that it use TCP/IP, as much as HTTP (Hyper Text Transfer Protocol)
World Wide Web
The world wide web (WWW or simply the web) give a graphical, easy to navigate interface for looking at documents on the internet. These documents as well as the links between them, comprise a web of information.
Files or pages on the web are interconnected. This connection is made by means of special text or graphics called hyperlinks.
Pages can contain text, image, moves, and sounds just about anything. These pages can be located on computers anywhere in the world. When a connection to the internet is made, it means equal access is available to information world side.
The computers that host web sites are called server; their service is to provide the documents that the clients request. Clients are the seemingly endless numbers of personal computers connected to the internet. Web browser, such as Interne Explorer (explained in the next section), helps to exploit the web.
Internet Explorer
Microsoft Internet Explorer is a web browser. Just as Microsoft word is a tool to create and format documents, or Microsoft excel is a tool to create spreadsheets and perform calculations, internet explorer is a tool to navigate and access, or “browse”, information on the web.
The internet Explorer toolbar provides a range of detailed functions and commands for managing the browser. The address bar below the toolbar displays the address of the current web page. Typing an address and hitting enter in it will enable to visit to the specified page. Clicking a hyperlink will also enable to jump to the new page. With Netscape dominating the web browser and server market, Microsoft, in the early 1996 introduced a new web browser and server to the internet community. Microsoft internet explorer is destined to be one of the most popular web browsers for several reasons. Not only is the browser easy to use and is supported by the world’s largest software company, it also supports several other specific HTML extensions. These include the following.
- Background sounds played automatically when the web page is loaded
- In line animations AVI files instead of graphic images
- Marquees that scroll across the browser window.
Working to the Internet
For a computer to be a server on the internet, it must have two things: an address by which other computers can locate it and the capability to understand and process the various protocols. A server is assigned a unique numeric ID called an IP (Internet Protocol) address. As the numeric address is very difficult to remember their corresponding domain name is used, which are in friendlier format such as http://www.Microsoft .Com.
The software used on the physical computer to make it a server that can speak the protocols of the internet and respond accordingly is called internet server software or web server such as Microsoft Internet information server.
For a client computer to be able to communicate with a server on the internet, it must have a connection to the internet. They, when connected, it must have a way to contact and receive data from internet servers through the various protocols. The connection is accomplished via an internet service provider (ISP), such as VSNL, satyam online, etc. The tool to communicate to the server and receive the data retuned by the internet server is handled by the internet browser, such as Internet Explore. The Figure 5.1 depicts the working of the internet.
Figure: Working of Internet