3 represents – 3-tier architecture.
User’s PC:- Users can access SAP system in two ways:-
Through Web browser
The Presentation Layer contains the software components that make up the SAPgui (graphical user interface). This layer is the interface between the R/3 System and its users. The R/3 System uses the SAPgui to provide an intuitive graphical user interface for entering and displaying data.
Database Layer :The Database Layer consists of a central database system containing all of the data in the R/3 System. The database system has two components – the database management system (DBMS), and the databse itself. SAP has manufactured its own database named HANA but is compatible with all major databases such as Oracle.All R/3 data is stored in the database. For example, the database contains the control and customizing data that determine how your R/3 System runs. It also contains the program code for your applications. Applications consist of program code, screen definitions, menus, function modules, and various other components. These are stored in a special section of the database called the R/3 Repository, and are accordingly called repository objects. R/3 repository objects are used in ABAP workbench.
ABAP+Java System Architecture
Dispatcher Queue: Various workprocess types are stored in this queue.
Dispatcher: It distributes requests to the workprocesses.
Gateway:It enables communication between SAP system and between SAP system and external systems.
ABAP-Workprocesses:- It separately executes dialog steps in R/3 applications.
Types of workprocesses are given as below:-
Message Server: It handles java dispatchers and server processes.It enables communication within java runtime environment.
Enqueue Server:It handles logical locks that are set by the executed Java application program in a server process.
Central Services:Java cluster requires a special instance of the central services for managing locks and transmitting messages and data. Java cluster is a set of processes that work together to build reliable system. Instance is group of resources such as memory, work processes and so on.
Java Dispatcher: It receives the client requests and forwards to the server process.
SDM: Software Deployment Manager is used to install J2EE components.
Java Server Processes: It can processes a large number of requests simultaneously.
Threading: Multiple Processes executes separately in the background , this concept is called threading.
ICM: It enables communication between SAP system and HTTP,HTTPS,SMTP protocol. It means by entering system URL in the browser you can access SAP from browser also.
Step 1) Once user click on the SAP system from GUI , User request is forwarded to Dispatcher .
For example , when user login to the system then Dialog workprocess is assigned to the user. If user runs a report in background then background workprocess is assigned to the user.When some modifications are done at database level then update workprocess is assigned.So as per user’s action workprocess is assigned.