- A view is a logical view on one or more tables. A view on one or more tables i.e, the data from a view is not actually physically stored instead being derived from one or more tables. A view can be used to summarize data which is distributed among several tables.
How many types of Views are there ? - Database View (SE11)
Database views are implement an inner join, that is, only records of the primary table (selected via the join operation) for which the corresponding records of the secondary tables also exist are fetched. Inconsistencies between primary and secondary table could, therefore, lead to a reduced selection set. In database views, the join conditions can be formulated using equality relationships between any base fields. In the other types of view, they must be taken from existing foreign keys. That is, tables can only be collected in a maintenance or help view if they are linked to one another via foreign keys.
- Help View ( SE54)
Help views are used to output additional information when the online help system is called. When the F4 button is pressed for a screen field, a check is first made on whether a matchcode is defined for this field. If this is not the case, the help view is displayed in which the check table of the field is the primary table. Thus, for each table no more than one help view can be created, that is, a table can only be primary table in at most one help view.
- Projection View
Projection views are used to suppress or mask certain fields in a table (projection), thus minimizing the number of interfaces. This means that only the data that is actually required is exchanged when the database is accessed. A projection view can draw upon only one table. Selection conditions cannot be specified for projection views.
- Maintenance View ( SE54 )
Maintenance views enable a business-oriented approach to looking at data, while at the same time, making it possible to maintain the data involved. Data from several tables can be summarized in a maintenance view and maintained collectively via this view. That is, the data is entered via the view and then distributed to the underlying tables by the system.
What is Locking ?
- When two users simultaneously attempt to access the same data record, this is synchronised by a lock mechanism.
When dialog transactions are programmed, locks are set and released by calling certain function modules. These function modules are generated automatically from the definition of so-called lock objects in the ABAP/4 Dictionary. To synchronize the access to a table by setting and removing locks, a Lock object has to be defined in the ABAP/4 Dictionary. Activating the lock object automatically creates #function modules for setting and removing locks. These function modules must be included when programming interactive transactions.
Lock Mechanism : To set locks, a lock object must be defined in the ABAP/4 Dictionary. In this lock object, those tables in which data records are to be locked by calling a lock are determined. All tables included in a lock object must be connected to each other via foreign keys. The key fields of the tables in a lock object form the Lock arguments for the tables. The lock arguments are the basis for formulating the logical condition for identifying the records to be locked. When activating this lock object, two function modulesB with the names ENQUEUE_ and DEQUEUE_ are generated.
Example :
Problem : You wish to prevent a user from being able to change the name of a course or the name of the professor with responsibility for the course at a time when another user is editing the course description (which contains this information).
Solution : The problem described above can be solved by defining a lock object E_UKURS. This is done by defining primary and secondary tables in the lock object. Table UKURS is check table of table UKRSB, so UKURS should be selected as primary table and UKRSB as secondary table of the lock object. The Lock argument in this case is the field combination FABNR, KRSNR, and SPRAS (i.e Primary Key Combination). The Lock mode Shared is to be selected here. This allows several users to access the data simultaneously in display mode. The lock mode in the generated function modules for setting (ENQUEUE_E_UKURS) and releasing (DEQUEUE_E_UKURS) locks is therefore set to shared as default, but can be overridden by calling the function modules. If the function module ENQUEUE_E_UKURS is called with FABNR = '1' and KRSNR = '3', the record for course 3 in faculty 1 is locked in table UKURS. Furthermore, all the course descriptions for this course are locked in table UKRSB since field SPRAS was not specified when the function module was called. In such cases, the lock is made generically for a field which is not defined. If the function module DEQUEUE_E_UKURS is now called with FABNR = '1', KRSNR = '3' and SPRAS = 'D', the German course description is unlocked. All other course descriptions remain locked.
What is database utility ?
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Database utility is the interface between the ABAP/4 Dictionary and the underlying the SAP system.
The database utility is the interface between the ABAP/4 Dictionary and the relational database underlying the SAP system. You can call the database utility from the initial screen of the ABAP/4 Dictionary with Utilities ® Database utility. The database utility allows you to create, delete and convert objects from the ABAP/4 Dictionary in the database. MODULARIZATION What is Modularization and its benefits? If the program contains the same or similar blocks of statements or it is required to process the same function several times, we can avoid redundancy by using modularization techniques. By modularizing the ABAP/4 programs we make them easy to read and improve their structure. Modularized programs are also easier to maintain and to update.
How can we create callable modules of program code within one ABAP/4 Program?
A. By defining macros. B. By creating include programs in the library.
What are subroutines?
Subroutines are program modules which can be called from other ABAP/4 programs or within the same program.
What are the types of Subroutines?
A. Internal Subroutines: The source code of the internal subroutines will be in the
same ABAP/4 program as the calling procedure (internal call).
B. External Subroutines: The source code of the external subroutines will be in an
ABAP/4 program other than the calling procedure.
What are the different types of parameters?
Formal parameters: Parameters which are defined during the definition of subroutine with the FORM statement. Actual parameters: Parameters which are specified during the call of a subroutine with the PERFORM statement.
How can one distinguish between different kinds of parameters?
A. Input parameters are used to pass data to subroutines. B. Output parameters are used to pass data from subroutines.
What are the different methods of passing data?
A. Calling by reference: During a subroutine call, only the address of the actual
parameter is transferred to the formal parameters. The formal parameter has no memory of its own, and we work with the field of the calling program within the subroutine. If we change the formal parameter, the field contents in the calling program also change.
B. Calling by value: During a subroutine call, the formal parameters are created as
copies of the actual parameters. The formal parameters have memory of their own. Changes to the formal parameters have no effect on the actual parameters.
C. Calling by value and result: During a subroutine call, the formal parameters are
created as copies of the actual parameters. The formal parameters have their own memory space. Changes to the formal parameters are copied to the actual parameters at the end of the subroutine.
The method by which internal tables are passed is By Reference.
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