Types of ABAP Programs
As in other programming languages, an ABAP program is either an executable unit or a library, which provides reusable code to other programs and is not independently executable.
ABAP distinguishes two types of executable programs:
- Reports
- Module pools
Reports follow a relatively simple programming model whereby a user optionally enters a set of parameters (e.g., a selection over a subset of data) and the program then uses the input parameters to produce a report in the form of an interactive list. The term "report" can be somewhat misleading in that reports can also be designed to modify data; the reason why these programs are called reports is the "list-oriented" nature of the output they produce.
Module pools define more complex patterns of user interaction using a collection of screens. The term “screen” refers to the actual, physical image that the user sees. Each screen also has a "flow logic", which refers to the ABAP code implicitly invoked by the screens. Each screen has its own flow logic, which is divided into a "PBO" (Process Before Output) and "PAI" (Process After Input) section. In SAP documentation the term “dynpro” (dynamic program) refers to the combination of the screen and its flow logic.
The non-executable program types are:
- INCLUDE modules
- Subroutine pools
- Function groups
- Object classes
- Interfaces
- Type pools
An INCLUDE module gets included at generation time into the calling unit; it is often used to subdivide very large programs. Subroutine pools contain ABAP subroutines (blocks of code enclosed by FORM/ENDFORM statements and invoked with PERFORM). Function groups are libraries of self-contained function modules (enclosed by FUNCTION/ENDFUNCTION and invoked with CALL FUNCTION). Object classes and interfaces are similar to Java classes and interfaces; the first define a set of methods and attributes, the second contain "empty" method definitions, for which any class implementing the interface must provide explicit code. Type pools define collections of data types and constants.
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