Complete Understanding of NetWeaver AS SAP ABAP
Complete Understanding of NetWeaver AS SAP ABAP
The following sections describe three different views of NetWeaver AS ABAP.
- Logical view
The difference between the logical view and a hardware or software oriented view of NetWeaver AS ABAP is that not all components shown can be assigned to a particular hardware or software unit. The following illustration represents this logical view in the form of a block diagram.
Below is a list of the activities of the three logical components in NetWeaver AS ABAP.
- Kernel and administration services
The kernel and administration services component is a runtime environment for all ABAP applications independent of hardware, operating system and database. The ABAP runtime environment is mainly written in C and C ++. However, some low-level parts are also written in the same ABAP. The kernel and administration services component activities are as follows:
- Running applications
All ABAP applications are run on software processors (virtual machines) within this component.
- User and process administration
NetWeaver AS ABAP is a multiuser environment and each user can run several independent ABAP applications. In short, this component is responsible for the activities that usually belong to an operating system. Users log into NW AS and run ABAP applications within it. In this way, they do not come into contact with the host's actual operating system. NetWeaver AS ABAP is the only user of the host operating system.
- Access to the database
Each ABAP NetWeaver AS is connected to a database system, consisting of a database management system (DBMS) and the database itself. ABAP applications do not communicate directly with the database. Instead, they use administration services.
- Communication
ABAP applications can communicate both with other SAP systems and with external systems. ABAP applications can also be accessed from external systems through a BAPI interface. The services required for communication are all part of the kernel component and administration services.
· Control and administration of NetWeaver AS ABAP
The component contains programs that allow you to monitor and control the NW AS while it is running and to modify its runtime parameters.
- ABAP workbench
The ABAP Workbench component is a complete development environment for ABAP language applications. With it, you can create, edit, test and organize these application programs. It is fully integrated into NetWeaver AS ABAP and, like other ABAP applications, it is itself written in ABAP.
- Presentation components
Presentation components are responsible for the interaction between ABAP applications and the user (input and output) and for the integration of desktop components (such as word processing and spreadsheets) into NW AS.
- Software oriented view
The following illustration represents the software-oriented view of an SAP system. In an ABAP-based SAP system, NetWeaver AS ABAP includes all the components of the SAP GUI and ABAP application servers.
An SAP system is a multilevel client / server system. The individual software components are arranged in levels and functions, depending on their position, as clients for the underlying components or servers for the components above them. The classic configuration of an SAP system contains the following software levels:
- Database level
The database layer, accessed by NetWeaver AS, is made up of a central database system which in turn is made up of the database management system (DBMS) and the database itself.
The database does not only contain the personal data and the transaction data of the ABAP application programs; all data for NetWeaver AS ABAP is stored there. For example, the database contains control and personalization of the data that determine how NetWeaver AS is run and the ABAP application programs themselves. The components (program texts, screen definitions, menus, function modules, etc.) are stored in a special part of the database known as the Repository and therefore are also called Repository objects. Work with them in ABAP Workbench.
- Application level
The application layer software components of NetWeaver AS ABAP consist of one or more ABAP application servers and a message server. Each application server contains a set of services used to run AS NW. Theoretically, only one application server is required to perform an AS NW. In practice, the services are distributed on more than one application server. This means that not all application servers will provide the full range of services. TheThe message server is responsible for communication between the application servers. Pass requests from one application server to another within an AS NW. It also contains information about application server groups and the current load balancing within them. Use this information to choose an appropriate server when a user logs on to the system.
- Presentation level
This level is the interface between the SAP system and its users. Using its software components referred to as SAP GUI (Graphical User Interface) this level provides an intuitive graphical interface for entering and viewing data. The presentation layer sends user input to the application server and receives data for viewing from it. While a SAP GUI component is running, it remains connected to a user's terminal session in NetWeaver AS ABAP.
This software-oriented view can be expanded to include additional layers, such as an Internet Transaction Server (ITS).
- Software oriented view and hardware view
The software-oriented view has nothing to do with the hardware configuration of the system. There are many different hardware configuration possibilities for both tiers and components. When distributing layers, for example, it is possible to have all the layers on a single host or, at the other extreme, you can have at least one host for each layer. When it comes to components, the distribution of database components depends on the database system you are using. Application layer and presentation layer components can be deployed on any number of hosts. It is also possible to install more than one ABAP application server on a single host. A common configuration is to run the database system and a single ABAP application server (containing special database services) on one host and to run each additional application server on its host. Presentation layer components usually run on users' desktop computers.
- Advantages of multilevel architecture
The distribution of the SAP system on three levels means that the system load is also distributed. This leads to better system performance. Another advantage is the high scalability obtained thanks to the fact that it is possible to distribute the software components of a SAP system among different hardware units practically without any restrictions. This is particularly useful at the application level, where NetWeaver AS ABAP can be adapted to meet growing demand by installing additional ABAP application servers.
The SAP system architecture allows you to install the application level and the database level on separate hosts and let them communicate over the network. This considerably reduces the load placed on the database system that contains the central data storage for NetWeaver AS ABAP and therefore must meet high demands while the system is running.
Likewise, separating the presentation and application layer reduces the load placed on the ABAP application servers by isolating the processing of user voices and formatting of data output from actual program execution. It is important to note that the SAP GUI and the ABAP application server are set up to reduce data movement between the two levels as much as possible. As a result, the presentation layer components can also be used on hosts that have slow connections to very distant application servers.
- User-oriented view
For the user, the visible components of the SAP system are those that appear as a window on the screen. These windows are created from the presentation layer of NetWeaver AS ABAP.
Before the user logs into the SAP system, he must launch a SAP GUI utility called SAP Login, which is installed on the front end. In SAP Access, the user chooses one of the available SAP systems.
The program then connects to the NetWeaver AS ABAP message server in the selected SAP system and obtains the address of a suitable (the lightest) ABAP application server. Then start a SAP GUI, connected to that application server. The SAP logon program is no longer needed for this connection.
SAP GUI starts the login screen. Once logged in, the user displays the SAP system home screen in a window on the screen. Within the SAP GUI, each window is represented as a session. After logging in, the user can open up to five additional sessions within the single SAP GUI. These behave almost like independent SAP applications. The different sessions allow you to run different applications in parallel, independently of each other.
Within a session, the user can run applications which in turn invoke additional windows (such as dialog boxes and graphic windows). These windows are not independent: they belong to the session from which they were called. These windows can be modal (the original window is not ready for input) or amodal (both windows are ready for input and interact with each other).
The user can open other SAP GUIs, using SAP access, to access the same system or another SAP system. The individual SAP GUIs and the corresponding terminal sessions of a user are totally independent. This means that you can have SAP GUIs that represent the presentation levels of different SAP systems open on the desktop computer.
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