The World Wide Web (WWW) is a system that enables users to find and retrieve information by navigating through linked hypertext documents. In a hypertext document, selecting a highlighted word, phrase, or image causes a new document or image or sound to be retrieved and displayed. WWW documents lead the user to skip from one document to another, retrieving information from servers scattered around the world.
Viewing a WWW document with a Windows graphical client such as Cello, WinWeb, Mosaic, or Netscape is much like reading a magazine. Textual information is displayed with typographic fonts. Color graphics can be supplemented by sound that can be played by clicking an icon embedded in the document. Web documents can be interactive in that they can respond to a user who clicks a button on the document to submit information to the Web server or to send e-mail to a predetermined address.
The World Wide Web is an application of client/server computing. Client software, known as a Web browser, sends a request for information from the user's computer to a server running on another computer. The server processes the request and returns a file to the browser. The returned file will normally be a hypertext document, which is often referred to as a WWW page. Other kinds of files also may be returned to the user.
If the returned file is a hypertext document, the browser software interprets the returned file and formats it for the user. During interpretation of a hypertext document, the browser may be instructed by links in the document to retrieve additional files. These additional files may be graphic images that are decoded by the browser and displayed inline with the text. Such links cause additional requests to be sent to the server to obtain the additional files. Thus, a single document request may result in numerous contacts between the browser and the server.
Some selections in hypertext documents may return files that are not themselves hypertext documents. Thus, it is possible that the file returned to the browser will be a Gopher menu from a Gopher server. In this case, the Web browser formats the Gopher menu for the user. The browser then substitutes for a Gopher client. Similarly, a file returned to the browser may be a directory from an FTP server. In this case the browser substitutes for an FTP client.
The file returned to the browser also could be an ASCII file or binary file from an FTP server. An ASCII file will usually be displayed by the browser as plain text with fixed line lengths. A binary file either will be saved to the user's local hard disk, or it will be passed to another application on the user's computer for further processing. Videos and sounds, and some images, typically are passed to "helper" applications or "viewers" for decoding and display.
Windows client and server software is based on the Winsock Applications Programming Interface (API). For a discussion of Windows client software and the Winsock standard, see my paper "Windows and TCP/IP for Internet Access." In addition to the hypertext version, a less current plain text (Release 07 | September 18, 1995 | 79,300 bytes) version is available. An earlier version is also available in print in the American Institute of Chemical Engineers "CAST Communications," Vol. 17, No. 2, pp. 6-14 (Summer 1994).