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Appendix C: Web Applications

NetExpress can be used for developing many kinds of COBOL application, from the most traditional to the most modern, but it is particularly suited to client/server applications, in which most data is kept on a central computer (the server) and accessed from many other computers (the clients). In such an application, queries are entered at a client, and software running locally forwards them to the server where software interrogates or updates the data and returns a response.

Nowadays most of the world's computer networks are connected together to form the Internet. A major use of the Internet is the World Wide Web, often called simply the Web. Computers known as Web servers store files known as Web pages, which can contain text and graphics, and run software to make them accessible across the Internet. Any computer running suitable software, called a Web browser, can access them. A Web page with fields for the user to fill in is called a Web form. Web server software can run programs (called server-side programs, or sometimes CGI programs after the most popular standard, Common Gateway Interface) to process data, and a Web browser can display forms sent to it by a Web server.

This is one example of a client/server application, and NetExpress is very suitable for designing Web business forms and server-side programs.

A Web page includes formatting commands in a language called HTML (HyperText Markup Language). If you're creating a Web page by hand you include these commands, but if you use NetExpress they are included for you.

There are several popular Web browsers on the market, and a Web page may look slightly different in different browsers.

Many companies and other organizations have their own intranet, with Web servers accessible only from computers within the organization. An application meant for an intranet works exactly like one intended for the World Wide Web, and people tend to use the term Web application for either.

Also, many organizations have a more traditional network. A file on a network server can be accessed from a network client as if the disk on the server were a disk on the client machine. NetExpress can also be used to create traditional client/server applications. Since the Internet is not involved, you use Windows-type graphical objects like windows and dialog boxes, instead of Web pages. We call these Windows GUI applications to distinguish them from Web applications. (You could of course use character-mode text input and output if you wished.)

Web forms, windows and dialog boxes can have objects on them such as pushbuttons, entry-fields, checkboxes, and so on. These are called controls.

If you want a longer and more detailed introduction to the World Wide Web, see the chapter Introduction to the World-Wide Web in the online book Internet Applications.

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