SAP ABAP/4 and R/3 System Overview SAP R/3:

SAP = System Applications and Products in Data Processing.

R/3 = Real Time Data Processing System with 3 Tire Architecture.
ABAP/4 = Advance Business Application Programming / 4th generation language.


Functional Modules or Application Areas of SAP:

1. Sales and Distribution
2. Financial Management
3. Fixed Asset Management
4. Quality Management
5. Production Planning
6. Plant Maintenance
7. Material Management
8. Controlling
9. Project System
10. Work Flow
11. Human Resource Management    etc.

Advantages of SAP R/3:

• Functionality - Software solution functions where all the commercial processes and transactions are done. 
• User Friendliness - GUI improves the user friendliness.
• Flexible Structure - R/3 system provides flexibility for every department.
• Real Time Integration - R/3 system provides real time integration.
• Enterprise Wide Integration - Due to flexibility system can change its application as per requirement of enterprise.
• Three Tier Architecture - It provides Presentation, Application and Database layer to the system.
• Desktop Integration - The system export and import data to the desktop by using export utility of system.
• Individual Solution - The system can be customized as per the requirement.

etc.

Functions of SAP R/3:

Integration with Saving time, Customizing the software according to the needs, Cost effective audits, Easy to learn and use, Good Information system etc.

SAP R/3 Landscape:
Development Server	Technical or functional people creates the programs or configuration as per the organisation’s requirement and send that to Quality server.
Quality Server	Team members test the development and configuration with various parameters and send that to Production server.
Production Server	The software is finally distributed to the clients through this Production server.

SAP R/3 System Architecture:
Presentation Layer	·         It provides the interface between users and R/3 system. ·         It provides the facility of SAP GUI. ·         It receives the user request as an input, forwards to application layer, in turn receives back the data from application layer and then sends back the data to the user.
Application Layer	·         It provides the interface between presentation and database layer. ·         It provides the set of executables to interpret ABAP/4 programs. ·         These executable begins when the application server starts and shuts down when the server stops.
Database Layer	·         It provides all data in the SAP R/3 system since it’s a centralized database system. ·         It accepts the request from application layer and passes that to the RDMS which sends back the required data to database layer.

Message Server:

It communicates between different application servers. Message server transfers the request from one application server to another within the system. 

User Context:

It is a temporary memory area which contains the information about users. When a user logs on an user context is allocated for that users. When the user logs off the temporary memory area is released. It holds the following information:

• User's Current Settings
• User's Authorization
• Name of the programs the user is using

Roll Area:

It is a temporary memory area which is allocated by work processes for program instance which is created by a user each time. This memory area becomes free when the program ends its execution. The roll area holds the following:

• The dynamic memory allocation
• Variables values
• The current pointer of the program

SAP Dispatcher:
It controls the resources of the R/3 application. It serves as a link between the user logged in and the work processes. It's main role is to receive request from the SAP GUI and transfer to work processes that are available. It's functions are:

• Making the connection with presentation layer
• Proper buffer management in main memory
• Assignment of work processes
• Proper organizing of communication process

Process Flow chart of SAP GUI and Dispatcher:

1. SAP GUI accepts the user input.
2. SAP terminal program then converts this input into SAP proprietary format.
3. Then it is sent to SAP dispatcher.
4. The dispatcher sends the processing request to request queues.
5. After that it is sent by one by one the available work process.
6. After completion of the processing of work process the result is sent to SAP dispatcher.
7. Then the dispatcher sends back to the SAP GUI.
8. Finally the GUI interprets the received data and generates the output field.

Work Process Structure:
Screen Processor	In R/3 system there is a special programming language called screen flow logic program. This program is executed by the screen processor through dispatcher. Hence the dispatcher makes communication between SAP GUI and work processes.
ABAP Processor	It receives the module of screen flow logic from the screen processor which is to be processed and sends that to database.
Database Interface	It establishes the connection between work processes and database and after that terminate the connection with database.

Different Types of Work Process:

• Dialogue work process
• Update work process
• Background work process
• ENQUEUE work process
• Spool work process

Logical Unit of Work (LUW):
Database LUW	It ensures the consistency of data in the database. Once the database LUW executes successfully then database becomes consistent. It either fully executes or not at all. In case of any error it goes back to the original state.
SAP LUW	It is a logical unit which comprises various dialogue steps.

SAP Memory and ABAP Memory:

SAP Memory	ABAP Memory
The area where all the main session can access SAP GUI.	The area where the entire ABAP program accesses within the same internal session.
It has global memory.	It has local memory.
It is available to user throughout the ending session.	It is available to user throughout the external session.
GET and SET parameters are used to send data between main sessions.	EXPORT and IMPORT statements are used to pass data between internal sessions.