Web Application Development

Introduction to Web Application Development

Web Technology

The growth of the World-Wide Web (WWW or simply Web) today is simply phenomenal. Each day, thousands more people gain access to the Internet (upwards of 6 million users at recent estimates). Easy retrieval of electronic information in conjunction with the multimedia capabilities of Web browsers (like Mosaic or Netscape) is what started this explosion. This document will provide some basic information behind some of this technology used in accessing the World-Wide Web.

History of World Wide Web (www)

First, a distinction: The Web and the Internet are not the same thing. The Web is a collection of standard protocols, or instructions, sent back and forth over the Internet to gain access to information. The Internet, on the other hand, is a "network of networks" a more physical entity.

The World-Wide Web began years ago by CERN (the European Laboratory for Particle Physics) who sought to build a distributed "hypermedia" system on the Internet. The term "hypertext" refers to the notion that one can click on a word or phrase displayed onscreen and a hotlink would cause it to jump to another text document, page, or section when selected. Extending this concept, "hypermedia" lets you click on something with your mouse and bring up not only text, but also graphics, sound, and animation. This "multimedia" capability is what drives the Web Until the release of the popular Web browser (a program used to read documents) called "Mosaic" (from the National Center for Supercomputing Applications), accessing online information was something only Computer Scientists and scholars did using text-based terminals. Since then, a colorful point-and-click graphical user interface, much like that on our Macintosh and Windows computers, makes surfing Cyberspace as easy a clicking a mouse.

WWW Component

Semantic Components

* Hypertext Transfer Protocol

The Web uses a language called Hypertext Transfer Protocol (HTTP) to talk to other computers connected to the Internet. In its simplest form, a client computer (like the one on your desk) talks to a Web server (a machine that has the information you want) using a dialog that roughly does the following:

* The client computer establishes a connection to the server.

* The client gives the server a request for a particular document.

* The server sends the document (if it is available).

* The two computers disconnect.

By not keeping a connection constantly open, a server can send out many thousands of files every hour to many different client machines. It makes for a more efficient way to distribute information to more people.

* Hypertext Markup Language

The Hypertext Markup Language (HTML) is a set of ever-changing standards of different universally accepted plain-text codes which are sent over a network (like the Internet) and describe the way a finished page should look to the user.

* Uniform Resource Locators

A Uniform Resource Locator (URL) is a structured addressing scheme which is used to tell your Web browser which server you want to connect to and what document you want it to send back to you once it makes the connection.

Structural Components

The WWW project is based on the principle of universal readership: "if information is available, then any (authorized) person should be able to access it from anywhere in the world. "JL The Web's implementation follows a standard client-server model. In this model, a user relies on a program (the client) to connect to a remote machine (the server), where the data is stored. The architecture of the WWW (see Figure 1) is the one of clients, such as Netscape, Internet Explorer, or Lynx, "which know how to present data but not what its origin is, and servers, which know how to extract data", but are ignorant of how it will be presented to the user.TC2

One of the main features of the WWW documents is their hypertext structure (see Figure 2). On a graphic terminal, for instance, a particular reference can be represented by underlined text, or an icon. "The user clicks on it with the mouse, and the referenced document appears."BCG This method makes copying of information unnecessary: data needs only to be stored once, and all referenced to it can be linked to the original document.

Web server

A Web server is a program that, using the client/server model and the World Wide Web's Hypertext Transfer Protocol (HTTP), serves the files that form Web pages to Web users (whose computers contain HTTP clients that forward their requests). Every computer on the Internet that contains a Web site must have a Web server program. Two leading Web servers are Apache, the most widely-installed Web server, and Microsoft's Internet Information Server (IIS). Other Web servers include Novell's Web Server for users of its NetWare operating system and IBM's family of Lotus Domino servers, primarily for IBM's OS/390 and AS/400 customers.

Web servers often come as part of a larger package of Internet- and intranet-related programs for serving e-mail, downloading requests for File Transfer Protocol (FTP) files, and building and publishing Web pages. Considerations in choosing a Web server include how well it works with the operating system and other servers, its ability to handle server-side programming, security characteristics, and publishing, search engine, and site building tools that may come with it.

* HTTP Server

"Web server" may refer to just the software and not the entire computer system. In such cases, it refers to the HTTP server (IIS, Apache, etc.) that manages requests from the browser and delivers HTML documents and files in response. It also executes server-side scripts (CGI scripts, JSPs, ASPs, etc.) that provide functions such as database searching and e-commerce.

* Open source

Open source usually refers to a program in which the source code is available to the general public for use and/or modification from its original design free of charge. Open source code is typically created as a collaborative effort in