ABAP stands for Advanced Business Application Programming, a 4GL (4th generation) language. Currently it is positioned, along with Java, as the main language for SAP application server programming.
The Presentation layer consists of any input device that can be used to control SAP system. This could be a web browser, a mobile device and so on. All the central processing takes place in Application server. The Application server is not just one system in itself, but it can be multiple instances of the processing system. The server communicates with the Database layer that is usually kept on a separate server, mainly for performance reasons and also for security. Communication happens between each layer of the system, from the Presentation layer to the Database and then back up the chain.
Note − ABAP programs run at the application server level. Technical distribution of software is independent of its physical location. It means basically all three levels can be installed on top of each other on one computer or each level can be installed on a different computer or a server.
ABAP programs reside inside the SAP database. They execute under the control of the runtime system that is a part of the SAP kernel. The run-time system processes all ABAP statements, controlling the flow logic and responding to user events.
So, unlike C++ and Java, ABAP programs are not stored in separate external files. Inside the database, ABAP code exists in two forms −
Source code that can be viewed and edited with the ABAP workbench tools.
Generated code, which is a binary representation. If you are familiar with Java, this generated code is somewhat comparable with Java byte code.
The run-time system can be considered as a virtual machine, just similar to Java virtual machine. A key component of the ABAP run-time system is the database interface that turns database independent statements (Open SQL) into the statements understood by the underlying database (Native SQL). SAP can work with a wide variety of databases and the same ABAP program can run on all of those.