ABAP application programs run on the work processes of the ABAP application servers of NetWeaver AS ABAP. This makes them independent of the hardware and operating system that you are using. However, it also means that you cannot run them outside NW AS ABAP.
As described in the Work Processes section, a work process contains a screen processor for processing user input, an ABAP processor for processing the program logic, and a database interface for communicating with the database. These components determine the following structure of an application program:
An ABAP application program consists of two components, each of which has a different task:
The application program components which react to user action on SAP GUI windowss are implemented using screens. Screens are processed by the screen processor of a work process. They contain screen masks and the screen logic which is programmed using a specific programming language similar to ABAP. The input mask is displayed by the SAP GUI, 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.
ABAP programs run on the ABAP processor of a work process. SAP GUI-based applications receive screen input from and send screen output 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.