1. Can anyone give me brief explanation about internal tables? An internal table is a run time instance. It gets created when program starts execution.

It gets destroyed when program terminates. It has two different parts: Header Line (optional) and Body (Compulsory).

Any value that comes to or goes from internal table, that travels through header line.

The size of the internal tables is set using the 'occurs n' clause. Here n refers to a integer number that specifies the size. Usually its given as 'occurs 0' which creates an itab with the memory space of 8kb

2. Explain row type and line type concept line type refers to the structure of an internal table, whereas row type is the actual part that contains the data and it refers to the table body. Creating internal table using line type and row type concept is for reusability purpose. Line type and Row type are defined at DDIC LEVEL.

3. What is the structure? There are three types of structure: - 1. Flat structure (elementary fields)2. Nested structure (type reference to other structure)3. deep structure (type reference to database tables)

4. Difference between “Insert”, “Update” and “Modify” INSERT - Add a new record into the database table. MODIFY - If record is available it modifies otherwise it won’t modify. UPDATE - If record is available its update the record otherwise it creates a new record.

5. How to eliminate duplicate entries in internal tables? SORT itab. DELETE ADJACENT DUPLICATES FROM itab COMPARING ALL FIELDS.

6. What are logical databases?Logical databases are special ABAP programs that retrieve data and make it available to application programs. The most common use is to read data from database tables by linking them to executable ABAP programs. It has also been possible to call logical databases using the function module LDB_PROCESS. This allows calling several logical databases from any ABAP program, nested in any way. Logical databases contain Open SQL statements that read data from the database so do not need to use SQL in programs. The logical database reads the program, stores them in the program if necessary, and then passes them line by line to the application program or the function module LDB_PROCESS using an interface work area.

7. What are the basic difference internal tables and database tables? Database tables are stored in DB server and the internal tables are virtual tables these are created run time only (dynamically) in the application server and it is external memory and terminates after the program termination. 

8. Can you create a table with fields not referring to data elements? YES. eg:- ITAB LIKE SPFLI. Here we are referring to a data object (SPFLI) not data element.

9. What are the central interfaces of the R/3 system? Presentation interface Database interface Operating system interface

10. What is SAP dispatcher? SAP dispatcher is the control agent which manages the resources for the R/3 applications.

11. What are the functions of dispatcher? Equal distribution of transaction load to the work processes Management of buffer areas in main memory Integration of the presentation levels Organization of communication activities.

12. What are the types of Update requests? An update request can be divided into one primary (V1) and several Secondary update components (V2). Time-critical operations are placed in V1 component and those whose timing are less critical are placed in V2 components. If a V1 update fails, V2 components will not be processed.

13. What is a Spool request? Spool requests are generated during dialog or background processing and placed in the spool database with information about the printer and print format. The actual data is placed in the Tem Se (Temporary Sequential objects).

14. 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.

15. What is the full name of SAP Default user DDIC.DDIC stands for DATA (D) DICTIONARY(DIC)- DDIC

16. How to schedule background jobs at OS level?

Invoke a sapevent using a OS script and then have a SAP background job set to run on a sapevent. I say this assuming Unix and a job in crontab. I would guess the same thing could be done on a Windows system.

sapevt TRIGGER_NAME -t pf=d:usrsapDEVsysprofileDEV_DVEBMGS00_SVRNAME nr