Question 1 :
What are presentation, application and database servers in SAP R/3?
The application layer of an R/3 System is made up of the application servers and the message server. Application programs in an R/3 System are run on application servers. The application servers communicate with the presentation components, the database, and also with each other, using the message server. All the data are stored in a centralized server. This server is called database server.
Question 2 :
What should be the approach for writing a BDC program?
Convert the legacy system data to a flat file and convert flat file into internal table. Transfer the flat file into sap system called "sap data transfer". Call transaction(Write the program explicitly) or create sessions (sessions are created and processed ,if success data will transfer).
Question 3 :
Explain open SQL vs native SQL?
ABAP Native SQL allows you to include database-specific SQL statements in an ABAP program. Most ABAP programs containing database-specific SQL statements do not run with different databases. If different databases are involved, use Open SQL. To execute ABAP Native SQL in an ABAP program, use the statement EXEC. Open SQL (Subset of standard SQL statements), allows you to access all database tables available in the R/3 System, regardless of the manufacturer. To avoid conflicts between database tables and to keep ABAP programs independent from the database system used, SAP has generated its own set of SQL statements known as Open SQL.
Question 4 :
What are datasets?
The sequential files (processed on application server) are called datasets. They are used for file handling in SAP.
Question 5 :
What are internal tables check table, value table, and transparent table?
Internal table: It is a standard data type object, which exists only during the runtime of the program. Check table: Check table will be at field level checking. Value table: Value table will be at domain level checking ex: scarr table is check table for carrid. Transparent table: - Exists with the same structure both in dictionary as well as in database exactly with the same data and fields.