What are the Basic Components of Dialog Program?

Answer

Unlike report which generally entails the creation of one autonomous program which can be executed independently of other objects, dialog program development entails development of multiple objects none of which can be executed on it's own. Instead all objects are linked hierarchically to the main program and and are executed in a sequence dictated by the Dialog Main Program.

The components of a dialog program are:

Transaction code

• The transaction code starts a screen sequence.
• You create transaction codes in the Repository Browser in the ABAP Workbench or using Transaction SE93.
• A transaction code is linked to an ABAP program and an initial screen.
• You can start a screen sequence from any ABAP program using the CALL SCREEN statement.

Screens

• Each dialog in an SAP system is controlled by one or more screens.
• You create screens using the Screen Painter in the ABAP Workbench through transaction SE51
• Each screen belongs to an ABAP program.
• These screens consist of a "screen mask" or "layout" and its flow logic. The screen has a layout that determines the positions of input/output fields and other graphical elements such as checkboxes and radio buttons. A flow logic determines the logical processing within screen.

GUI status

• Each screen has a GUI status(es) which are independent components of a program.
• This controls the menu bars, standard toolbar, application toolbar , with which the user can choose functions in the application.
• You create them in the ABAP Workbench using the Menu Painter.

ABAP Program

• Each screen and GUI status in the R/3 System belongs to one ABAP program.
• The ABAP program contains the dialog modules that are called by the screen flow logic, and also process the user input from the GUI status.
• ABAP programs that use screens are also known as dialog programs.
• In a module pool (type M program); the first processing block to be called is always a dialog module. However, you can also use screens in other ABAP programs, such as executable programs or function modules. The first processing block is then called differently; for example, by the runtime environment or a procedure call. The screen sequence is then started using the CALL SCREEN statement.

Screen Flow Logic

Screen Flow logic is primarily divided into four components.

• Process Before Output (PBO) event: which is processed before the screen is displayed
• Process After Input (PAI) event: which is processed after a user action on the screen
• Process on help request (POH): which is processed when F1 is pressed
• Process on value request (POV):which is processed when F4 is pressed

Dynpro

• A screen together with its Flow logic  is called a Dynpro ("Dynamic Program" since the screen flow logic influences the program flow)
• Each dynpro controls exactly one step of your Dialog Program.
• The screens belonging to a program are numbered. The  screen flow sequence can be either linear or cyclic. From within a screen chain, you can even call another screen chain and, after processing it, return to the original chain. You can also override the statically-defined next screen from within the dialog modules of the ABAP program.

ABAP Module Pool

• On a PBO or PAI event a Dynpro calls an ABAP dialog program.  Collection of such programs is called the ABAP module pool.
• For example modules called at the PAI event are used to check the user input and to trigger appropriate dialog steps, such as the update task.
• All dynpros to be called from within one transaction refer to a common module pool.