Theorical question

[Former Member]

Hi!

Does anyone know some information about the SAP layers? I mean the presentation, database and the application layers?

I'm interested about information on the application and the database layers... What are they doing, how are they communicating, etc...

Thank you

Tamá

[Former Member]

Presentation Server

The presentation server is actually a program named sapgui.exe. It is usually installed on a user's workstation. To start it, the user double-clicks on an icon on the desktop or chooses a menu path. When started, the presentation server displays the R/3 menus within a window. This window is commonly known as the SAPGUI, or the user interface (or simply, the interface). The interface accepts input from the user in the form of keystrokes, mouse-clicks, and function keys, and sends these requests to the application server to be processed. The application server sends the results back to the SAPGUI which then formats the output for display to the user.

Application Server

An application server is a set of executables that collectively interpret the ABAP/4 programs and manage the input and output for them. When an application server is started, these executables all start at the same time. When an application server is stopped, they all shut down together. The number of processes that start up when you bring up the application server is defined in a single configuration file called the application server profile. Each application server has a profile that specifies its characteristics when it starts up and while it is running. For example, an application sever profile specifies: · Number of processes and their types · Amount of memory each process may use · Length of time a user is inactive before being automatically logged off The application server exists to interpret ABAP/4 programs, and they only run there-the programs do not run on the presentation server. An ABAP/4 program can start an executable on the presentation server, but an ABAP/4 program cannot execute there. If your ABAP/4 program requests information from the database, the application server will format the request and send it to the database server.

Database Server

The database server is a set of executables that accept database requests from the application server. These requests are passed on to the RDBMS (Relation Database Management System). The RDBMS sends the data back to the database server, which then passes the information back to the application server. The application server in turn passes that information to your ABAP/4 program. There is usually a separate computer dedicated to house the database server, and the RDBMS may run on that computer also, or may be installed on its own computer.

also refer

http://web.mit.edu/its-alive/it_partners102500/sld005.htm

and

http://www.informit.com/content/images/0130280844/samplechapter/0130280844.pdf

regards,

srinivas

[Former Member]

Check this link

http://help.sap.com/saphelp_47x200/helpdata/en/54/57fe09786a11d194c90000e8353423/content.htm

[JanStallkamp]

Hi.

I'm not sure that you ask your question in the right forum here. The database experts usually hang around in the database and operating system forums. And there are other forums for application server experts, too.

If you're only interested in the ABAP part than most likely you don't have to care about the database layer at all. It's there. As long as you only use OpenSQL for your data access you will not need to know much about the layers behind.

If you want to know some basics about the layer concept... I will try to explain it in a few lines:

- the database layer: storing the data. This is done by a database. SAP supports several of them like IBM's DB2 family, Oracle and some others. On top of this databases is some software that gives a common interface to them. If you are into details: look for DBSL.

There is allways <i>one</i> database behind an SAP system

- the application layer: processing the data. Doing calculations, running processes... That's the ABAP world. You can have multiple application servers.

- presentation layer: what the user sees on his screen. SAPGui or WebDynpro in the browser.

Regarding communication: You should try to reduce the communication needed between layers. Only transfer data to the presentation layer that is needed there. For example don't send an 30MB table to the browser (user perhaps connected via slow modem) if the user only want's to see one line of the table. Same for the communication to the database layer. So don't read a whole database table into an internal table and then select one line of it afterwards. Do the selection when reading the data.

Hope that helped a little bit.

Best regards,

Jan