This section describes the architecture of SAP.
The design of the SAP NetWeaver Application Server aims to provide an exceptionally high level of robustness and maintainability for the applications running on it. SAP based the architecture of R/3 on a three-tier client/server model.
The presentation server is a program named sapgui.exe usually installed on the user's workstation. To start it, the user double-clicks on the icon or chooses a menu path. The presentation server then displays the R/3 menus in a window commonly known as the SAPGUI, the user interface, or simply the interface. The interface accepts input from the user in the form of keystrokes, mouse-clicks, and function keys, and then sends these requests to the application server to be processed. The application server sends the results back to the SAPGUI, which formats the output to display it to the user.
The application server is a set of executables that collectively interpret the ABAP/4 programs and manage the input and output for them. When the application server starts, these executables all start at the same time. When the application server stops, they all shut down. The number of processes that start when you launch the application server is defined in a single configuration file called the application server profile.
The database server is a set of executables that accept database requests from the application server. These requests are passed on to the Relation Database Management System (RDBMS). The RDBMS sends the data back to the database server, which sends it back to the application server. The application server then sends the information to your ABAP/4 program.