R/3’s system architecture Interview Questions

1. What is the function of the SAP Dispatcher?
The SAP Dispatcher is the proprietary control agent which, along with the respective operating system, manages the resources for the R/3 applications.
The main tasks of the dispatcher are:
1) Equal distribution of transaction load to the work processes.
2) Management of buffer areas in main memory.
3) Integration of the presentation level.
4) Organization of communication activities.

2. What is a Work Process and identify the ones within R3.
A work process is where individual dialog steps are actually processed and the work is done. Each work process handles one type of request:
online, (process only one request at a time),
background, (started at a specified time),
update, (primary, U1, or secondary U2),
enqueue, (lock mechanism)
spool, (generated online or during background processing for printing).

3. In R3 there are 2 services that deal with communication. Identify and explain their function.
1) Message service: used by the application servers to exchange short internal messages, all systems communication.
2) Gateway service: enables communications between R/3, R/2 and external applications, using the CPI-C protocol. Also used by EDI, RFC, which are:
RFC: remote function calls, internal tables are passed on "with references". A copy of the table is copied to thee target system, updates performed using only the one log table. Data transfer may be synchronous or asynchronous. Batch input sessions are also a possibility.
EDI: electronic data interchange; converts the temporary structures to EDI messages and vice-versa (SAP does not provide this element of the EDI architecture). Automatic processing of business transactions.

4. Understand/Describe the data flow of a Dialog Step.
First, user input is accepted by SAPGUI. SAPGUI is the SAP software that runs on your PC. SAPGUI converts the users input into process requests that the dispatcher can understand, and then sends the process requests to the dispatcher.
After receiving the process request the dispatcher places it into request queues called the Roll and Page areas.
As work processes become available the dispatcher dispatches the queued process request to the appropriate work process. The actual processing takes place in the work process.
Work processes are specialized components of the SAP software that are designed to very specific activities. For example if the dispatcher receives a process request to print a report, that process request will inevitability find its way to the work process that manages the print spool.
When processing is complete, the result of a work process is returned, via the dispatcher, to the SAPGUI. The SAPGUI interprets the received data and generates the output screen for the user.

5. Which work process triggers database changes?
Online work processes can directly trigger database changes, but the update work process is normally local to the database and thus has shorter communication path.