R/3 application programs run within the R/3 Basis system on the work processes of application servers. This makes them independent of the hardware and operating system that you are using. However, it also means that you cannot run them outside the R/3 System.

Interaction between application programs and the user is implemented using screens. Screens are processed by the screen processor of a work process. As well as the input mask, they consist of flow logic. This is coding, written using a special set of keywords called the screen language. The input mask is displayed by the SAPgui, which also transfers the user action on the screen back to the flow logic. In the program flow, screens react to the user actions and call program modules. These program modules form the processing logic.

The components of application programs that are responsible for data processing in the R/3 System are ABAP programs. ABAP stands for ‘Advanced Business Application Programming’. ABAP programs run on the ABAP processor of a work process. They receive screen input from the screen processor and send it to the screen processor. You access the database using the database interface. ABAP contains a special set of commands called OPEN SQL. This allows you to read from and write to the database regardless of the database you are using. The database interface converts the OPEN SQL commands into commands of the relevant database. You can also use native SQL commands, which are passed to the database without first being converted. There is a range of further interfaces such as memory, sequential files and external interfaces. These provide other means of sending data to and from ABAP programs. When working together with screens, ABAP programs play a more passive role, acting as a container for a set of modules that can be called from the flow logic.