sap netweaver application server java_SAP NetWeaver Application Server Architecture
SAP NetWeaver comprises something called Application Server ABAP
- there is even an own area reserved for it in SDN - but what is
Application Server ABAP? What is its role in SAP NetWeaver and
which services does it offer? To solve this question, we must have
a look at the different usages of the term "application server" in
the ABAP environment.
SAP NetWeaver Application Server
SAP NetWeaver offers of a set of different components - so
called "usage types". Important "usage types" include:
Business Intelligence (BI)
SAP NetWeaver Portal (EP)
Mobile Infrastructure (MI)
Process Integration (PI)
Application Server (AS)
The "usage type" Application Server (AS) plays a very central
role. It is responsible for the persistent storing of data and its
processing. For this, it offers programming interfaces that allow
other components of SAP NetWeaver, such as the SAP NetWeaver
Portal, to request data, have it edited, or store it. The primary
data storage of a NetWeaver AS is usually a central database.
The application server essentially offers two programming
interfaces, ABAP and Java. Or in other words, the Application
Server "usage type" in SAP NetWeaver comprises two "usage types":
the Application Server ABAP (AS ABAP) and the Application Server
Java (AS Java). Both application servers work on different data
(different database schemes that can nevertheless be located in the
same database). When you install an application server, you can
install either one of the two variants, or you can install both
variants at the same time. Then, they are linked together via a
special programming interface, the so called Java Connector
(JCO).
Application Server ABAP
The Application Server ABAP (AS ABAP) allows you to program
applications in ABAP. For this it provides the ABAP runtime
environment (a virtual machine for ABAP programs), the ABAP
Workbench, and an integrated change and transport system (CTS). The
following figure shows shows an overview of its most important
components.
AS ABAP can be used either by people using user interfaces (Web
Browsers or SAP GUI) or by other software components through the
network. For the latter two main protocols are used:
HTTP/HTTPS/SMTP for Internet connections (controlled by the
so-called Internet Communication Manager, ICM) and SAP’s own
Remote Function Call (RFC) protocol (via the RFC interface).
Most of the components of AS ABAP can be divided into three
layers:
Presentation Layer
These components are responsible for the presentation of data for
users and the receiving of user entries. When web browsers are used
as user interfaces, HTML pages prepared in the presentation layer
are accessed by application programs through the classes and
interfaces of the Internet Connection Framework (ICF), which wrap
the HTML pages. The presentation in a web browser is based on Web
Dynpro ABAP (MVC-based technology for creating platform-independent
web-based interfaces) and also still Business Server Pages (BSP,
HTML pages that incorporate server-side scripts written directly in
ABAP). When you use the SAP GUI that is available in versions for
MS Windows, Java and Web Browser, user interfaces are displayed in
windows that are based on the (classical) dynpro technology. The
layout of a dynpro can contain a set of predefined screen elements
or GUI controls (wrapped by the classes of a Control Framework,
CFW).
Application Layer
Here, application programs are executed. The application layer
contains a kernel written primarily in C/C++ that serves as a
platform for the application programs. The kernel of AS ABAP
provides Virtual Machines for ABAP with ABAP Objects (main
programming interface of AS ABAP for business applications), XSLT
and ST (transformation languages for transforming ABAP data to XML
and vice versa), and still JavaScript (obsolete, server-side
scripting in BSPs beside ABAP).
Persistence Layer
Here, persistent data is held in a database. The database is
accessed by ABAP programs through the database interface of AS ABAP
that is subdivided into an Open SQL interface and a native SQL
interface. Open SQL is a subset of the Structured Query Language
(SQL) realized directly by ABAP statements. Native SQL are
database-specific SQL instructions that are passed directly to the
database system (either statically or dynamically via ADBC).
The other components are communication components:
Internet Communication Manager (ICM)
The ICM allows the AS ABAP to communicate with the Internet via
HTTP/HTTPS/SMTP. It is the basis for webbased presentation
components such as Web Dynpro ABAP and BSP and it enables an AS
ABAP to act both as a client and as a server for Web services ABAP
programs access the ICM through the classes and interfaces of the
Internet Communication Framework (ICF)
RFC Interface
Classical functional interface of AS ABAP. A Remote Function Call
(RFC) is an invocation of a function that is located in a different
system than the one in which the calling program is running. Calls
are possible between different AS ABAPs, or between an AS ABAP and
another system (JCO communication also takes place via the RFC
interface).
More Application Servers ...
Now, that we know the Application Server ABAP, what other
application servers do we have to look at? Well, the application
layer of the AS ABAP is not a single unit, but is distributed
across several parallel software units to make it scalable. These
software units are connected by a message server and for historical
reasons are also called application servers.
With other words: one AS ABAP (sy-sysid) can be distributed over
several application servers. Usually these application servers are
installed on several machines. As a matter of fact, each
application server can handle only its own memory (programs, data)
and there is no access to the memory of other application servers,
even within the same AS ABAP. Each application server provides a
range of services that are implemented by so-called work processes.
Each ABAP program is executed by an appropriate work process on
such an application server. Each work process is connected to the
central database of the AS ABAP as a user.
In short: ABAP programs run on application servers that
communicate with the presentation layer, the central database
layer, and between each other via the message server. An ABAP
program can only access memory that belongs to the current
application server.
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