It is the code that processes a screen in SAP. The various event blocks of flow logic are as follows
Process Before Output PBO
Code that is executed before the current screen is displayed
Process After Input PAI
Code to be executed when the user does any interaction with the screen. At the end of PAI the system goes to the PBO of the next or the current screen
Process on Help-Request POH & Process on Value-Request POV
Code to be executed when the user presses F1 or F4 respectively. At the end the system continues with the processing of the current screen
Syntax of the flow logic statements is similar to ABAP, but all ABAP key words can not be used in the flow logic. The following keywords can be used with the event blocks
Module Calls a dialog module
Field Indicates when screen field contents are transported
On Used with Field
Values Used with field
Chain Start of processing of chain of fields
Endchain End of processing of chain of fields
Call Calls a subscreen
Loop Start of processing of screen table
Endloop End of processing of screen table
To summarize
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A Transaction is a collection of screens and ABAP routines, controlled and executed by a dialog processor. Only one module pool can be associated with a transaction.
A module pool is a collection of screens, which are invoked in a pre-defined sequence to complete the task that needs to be performed.
