In any processing block of an ABAP program, you can call
When a program is called, the calling program can be exited either temporarily or completely.
For a temporary exit from the calling program, the called program is started in a new internal session. The internal session of the calling program is retained. The calling program and the called program represent a call sequence. Within a call sequence, the programs have shared access to the ABAP Memory (statements IMPORT FROM MEMORY and EXPORT TO MEMORY). A call sequence can have a maximum of nine internal sessions. If this maximum is exceeded, the program terminates and the entire call sequence is deleted.
When the calling program is completely exited, the called program is started in a new internal session, which replaces the internal session of the calling program.
A program that generates an internal session when it is called, represents the main program of the main program group in the internal session.
When the runtime environment loads a called program, the event LOAD-OF-PROGRAM is triggered in that program.