When a request from Presentation Server first comes to the
Application Server, it directs the request to the dispatcher. The dispatcher,
which is the Central process of the SAP Web Application Server, manages the
resources for the applications written in ABAP in coordination with the
respective operating system. The main tasks of the ABAP dispatcher include the
distribution of the transaction load to work processes, the integration of the
presentation layer and the organization of communication transaction. The
requests are first saved in the queue by the dispatcher and then processed according
to the principle of “first-in, first-out.” The dispatcher distributed the
request one after another to the available work processes. A work process
handles one request at a time. Data is actually processed in the work process,
although the user who created the request using the SAP GUI is not always
assigned the same work process.
There is no fixed assignment of work process to users. To
process user request it might be necessary to read data from the ABAP schema of
the database or to write to it. For this, every work process is connected
directly to the ABAP schema of the database.
Once the process is complete, the processing result from the
work process is sent via the dispatcher back to SAP GUI. The SAP GUI interprets
the received data and generates the output screen for the user with the help of
the operating system on the front end computer.
The buffer helps to speed up processing of user requests.
Data that is often read but seldom changed (for example, program or Customized
data such as clients, currencies or company codes) can be kept as a copy of the
database content in the shared memory of the application server. This means
that data does not have to read from the database every time it is needed, but
can be called very quickly from the buffer.
Processing Web Requests
Web requests are accepted by an Internet Communication
Manager (ICM). These HTTP(S) request can either be processed in the ABAP work
process (such as BSP applications) or they can be requests for SAP Web
Application Server Java. The ICM can use the URL to decide to where it forwards
The next tier is the database server where the actual RDBMS
lies. This layer holds the system – wide database and the central booking
process of the SAP R/3 architecture. The Database layer is comprised of a
central database system, which contains all the data in the R/3 system. The
database system has two components – the database management system (DBMS) and
the database itself. The R/3 support the database system from the suppliers,
such as ADABAS D, DB2/400 (on AS/400), DB2 Common Server, DB2/MVS, INFORMIX,
Microsoft SQL Server, ORACLE, and ORACLE Parallel Server; SAP does not
manufacture its own database.
The database not only contains the master data and
transaction data from your business applications, but also the data for the
entire R/3 system is stored here.
The distribution of the R/3 software over the three layers
means that the system load is also distributed. This leads to better system performance.
Since the database system contains all of the data for the entire R/3 system,
it is subject to a very heavy load when the system is running. It is a good
idea not to run the application programs on the same host. The architecture of
the R/3 system (with Application layer and Database layer separate) allows you
to install them on separate hosts and let them communicate using the network.
It also makes sense to separate program execution from the
tasks of processing user input and formatting data output. This is made
possible by separating the presentation layer and the Application layer. SAP
GUI and the application servers are designed so that a minimum amount of data
is transported between the two layers. This means the Presentation Layer
components can even be used on hosts that have slow connections to application
The system is highly scalable – the software component of an
R/3 system can be distributed in almost any configuration across various hosts.
This is particularly valuable in the Application layer where you can easily
adopt your R/3 system to meet the increasing demand by installing further
Integration is the key element that separates SAP from other
enterprise applications. Integration helps in connecting a business environment
from Financial and Human Resources to Manufacturing and Sales and Distribution.
Integration in SAP means that all the business processes of
any organization are related and interspersed with each other so that a change
in one field of the business will reflect on another field of the business.