Oracle Applications environment
Network Computing Architecture provides Oracle Applications with a framework for multi-tier, distributed computing. In the multi-tier computing model, various functions of the Oracle Applications architecture are distributed among multiple levels, or tiers, of computers. Although many computers can be used in a configuration, scalability derives from processing capabilities on three separate tiers: the desktop client tier, the application tier, and the database tier. A two-tier environment consists of the desktop client tier and the database tier. A three-tier environment consists of the desktop client tier, the application tier, and the database tier.
Desktop client tier
The desktop client runs a Java applet using a Java-enabled web browser or applet viewer. The applet sends user requests to the forms server and handles such responses as screen updates, pop-up lists, graphical widgets, and cursor movement. A web browser or applet viewer manages the downloading and storage of the Forms client applet on each user's desktop. They also supply the Java Virtual Machine that runs the Forms client applet.
Application tier
Application servers are used as the middle tier between the desktop clients and the database server. They provide load balancing, business logic, and other functionality. The application tier is present only in a three-tier environment.
The forms server is a specific type of application server that hosts the Oracle Forms Server engine. The Oracle Forms Server mediates between the desktop client and the Oracle database server, displaying client screens and causing changes in the database records on user actions. Data is cached on the forms server and provided to the client as needed. The forms server exchanges messages with the desktop client across a standard TCP/IP network connection. Automatic load balancing can be achieved among forms servers with Metrics Server configuration. The Metrics Server is a single coordinator located on one application server. Metrics Clients located on the other application servers periodically send load information to the Metrics Server so it can determine which has the lightest load. When a client issues a request to download the Forms client applet, the Metrics Server provides the name of the least-loaded host for the applet to connect to.
The web server is another type of application server, which runs an HTTP listener. The HTTP listener is a component of an HTTP server. This listener accepts incoming HTTP requests from desktop clients, via the web browser or applet viewer. The requests are either immediately processed for HTML documents or are passed to the Oracle Web Application Server to access the forms server which connects to the database.
When configuring a middle tier web server to monitor Oracle Applications versions earlier than 11i, PATROL automatically selects an Oracle Web Server to be configured. When monitoring Oracle Applications version 11i or later, an Apache Server is selected for configuration.
Database tier
The database tier holds all the data and data-intensive programs, and processes all SQL requests for data. The database tier includes Oracle database server, the administration server, and the concurrent processing server. Computers in the database tier do not communicate with desktop clients directly, but through computers in the middle application tier.
The Oracle database server contains the data associated with Oracle Applications. The administration server is the machine from which various maintenance tasks, such as installation and updates, are performed. The concurrent processing server is used to process background programs such as reports. In Oracle Applications Releases 11, 11i, and 12, these three servers can be located on different computers.