Middle Tier

The Forms runtime engine running on the middle tier (application server) accesses the file system on the server (or another networked location) and presents the user interface layer in a Java applet on the client tier. The application server in this environment is essentially the same as the client tier of the client/server environment. It runs the runtime engine (called Forms Services) that is a separate process or Java servlet and accesses the file system for Forms files and the database for data. It is critical to remember that the form presented in the client’s browser is actually running on the middle tier with only the presentation layer revealed on the client’s side. The client is considered “thin” from a software standpoint because it does not need to store the Forms runtime programs or the Forms application files. The application server stores the runtime files and a Forms runtime process or servlet process(shown in Figure B as the runtime engine). There are other web components that also run on the middle tier to start a runtime session: the Forms Server and the HTTP listener (Oracle9i application server or any non-Oracle web server such as Netscape Enterprise Server, Microsoft Internet Information Server, or Apache). The Forms Server and the HTTP listener are not used while a form is running, although the Forms Server is used to start the form. The database server runs the database software to manage the database files the same way it does in the client/server model. The only real difference between the client/server and a multi-tier model is that the multi-tier client is split into two machines: the application server tier and the client. The database server is the same in client/server and multi-tier models.