ABAP Frequently asked questions on Basis Layer

What are the central interfaces of the R/3 system ?

Presentation interface
Database interface
Operating system interface

Which interface controls what is shown on the p.c. ?

Presentation interface

Which interface converts SQL requirements in the SAP development system to those of the database ?

Database interface

What is SAP dispatcher ?

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

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 actives.

What is a work process ?

A work process is where individual dialog steps are actually processed and the work is done. Each work process handles one type of request.

Name various work processes of R/3 system ?

1) Dialog or Online ( processes only one request at a time )
2) Background ( started at a specified time )
3) Update ( primary or secondary )
4) Enque( lock mechanism )
5) Spool ( generated online or during back ground processing For printing )

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.

What are the roll and page areas ?

Roll and page areas are SAP R/3 buffers used to store
user contexts ( process requests ) . The SAP dispatcher assigns
process requests to work processes as they are received. If
the work process is unavailable the process requests are queued in the roll and page areas.
Paging area holds data from the application programs.
Roll area holds data from previous dialog steps and data that characterizes user.

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).

What are the different database integrities ?

Semantic integrity
Relational integrity
Primary key integrity
Value set integrity
Foreign key integrity and
Operational integrity.


Type of a table or structure

The table type determines how the logical table description defined in the ABAP/4 Dictionary is reproduced on the database.

There are the following table types:
transparent table
append structure

For internal purposes, such as storing control data or update texts,
there are in addition the following table types:
pooled table
cluster table
generated view structure

Transparent table :

There is a physical table on the database for each transparent table. The names of the physical tables and the logical table definition in the ABAP/4 Dictionary correspond. All business data and application data are stored in transparent tables.

Structure :

No data records exist in the database for a structure. Structures are used for the interface definition between programs or between screens and programs.

Append structure:

An append structure defines a set of fields which belong to another table or structure but which are treated in the correction administration as its own object. Append structures are used to support modifications.

Pooled table :

Pooled tables can be used to store control data (e.g. screen sequences, program parameters or temporary data). Several pooled tables can be combined to form a table pool. The table pool corresponds to a physical table on the database in which all the records of the allocated pooled tables are stored.

Cluster table:

Cluster tables contain continuous text, for example, documentation.Several cluster tables can be combined to form a table cluster. Several logical lines of different tables are combined to form a physical record in this table type. This permits object-by-object storage or object-by-object access. In order to combine tables in clusters, at least parts of the keys must agree. Several cluster tables are stored in one corresponding table on the database. Generated view structure: In activation a structure is generated for a view. This structure serves interface for the runtime environment. It does not generally appear in the ABAP/4 Dictionary.

What is a Data Class?

The Data class determines in which tablespace the table is stored when it is created in the database.

What is a Size Category?

The Size category describes the probable space requirement of the table in the database.

How Many types of size categories and data classes are there?

There are five size categories (0-4) and 11 data classes, only three of which are appropriate for application tables:

APPL0 - Master data (data frequently accessed but rarely updated)
APPL1 - Transaction data (data that is changed frequnetly)
APPL2 - Organisational data (customizing data that is entered when system is configured and then rarely changed)

What are control tables?

The values specified for the size category and data class are mapped to database-specific values via control tables.

What is the function of the transport system and workbench organizer?

The function of the transport system and the Workbench Organizer is to manage any changes made to objects of the ABAP/4 Development Workbench and to transport these changes between different SAP systems.

What is a table pool?

A table pool (or pool) is used to combine several logical tables in the ABAP/4 Dictionary. The definition of a pool consists of at least two key fields and a long argument field (VARDATA).

What are pooled tables?

These are logical tables which must be assigned to a table pool when they are defined. Pooled tables can be used to store control data (such as screen sequences or program parameters).

What is a table cluster?

A table cluster combines several logical tables in the ABAP/4 Dictionary. Several logical rows from different cluster tables are brought together in a single physical record. The records from the cluster tables assigned to a cluster are thus stored in a single common table in the database.

Which objects are independent transport objects?

Domains, Data elements, Tables, Technical settings for tables, Secondary indexes for transparent tables, Structures, Views, Matchcode objects, Matchcode IDs, Lock objects.

What are the Data types of the external layer?

What are the Data types of the ABAP/4 layer?
Possible ABAP/4 data types:
C: Character.
D: Date, format YYYYMMDD.
F: Floating-point number in DOUBLE PRECISION (8 bytes).
I: Integer.
N: Numerical character string of arbitrary length.
P: Amount or counter field (packed; implementation depends on hardware platform).
T: Time of day HHMMSS.
V: Character string of variable length, length is given in the first two bytes.
X: Hexadecimal (binary) storage.

How can we set the tablespaces and extent sizes ?

You can specify the extent sizes and the tablespace (physical storage area in the database) in which a transparent table is to be stored by setting the size category and data class.

What is a data dictionary ?

Data dictionary is a central source of data in a data management system. Its main function is to support the .It has details about

What data is contained ?
What are the attributes of the data ?
What is the relationship existing between the various data elements ?
What functions does a data dictionary perform ?
In a data management system, the principal functions performed by the data dictionary are
Management of data definitions
Provision of information for evaluation
Support for software development
Support form documentation
Ensuring that the data definitions are flexible and up-to-date.

A field containing currency amounts (data type CURR) must be assigned to a reference table and a reference field. Explain.

As a reference table, a system table containing all the valid currencies is assigned or any other table which contains a field with the currency key format. This field is called as reference field.
The assignment of the field containing currency amounts to the reference field is made at runtime. The value in the reference field determines the currency of the amount.

What is the significance of Technical settings (specified while creating a table in the data dictionary) ?

By specifying technical settings we can control how database tables are created in the database.The technical settings allows us to optimize storage space requiremnets table access behavior buffering required changes to entries logged

What is the significance of Delivery Class ?

The delivery class controls the degree to which the SAP or the customer is responsible for table maintenance whether SAP provides the table with or without contents.
determines the table type.
determines how the table behaves when it is first installed, at upgrade, when it is transported, and when a client copy is performed.

What is the maximum number of structures that can be included in a table or structure


What are the two methods of modifying Sap standard tables ?

Append Structures and
Customizing Includes.

What is the difference between a Substructure and an Append Structure ?

In case of a substructure, the reference originates in the table itself, in the forma of a statement .include... .

In case of an append structure, the table itself remains unchanged and the refrence originates in the append structure.

What are the two ways for restricting the value range for a domain ?

By specifying fixed values.
By stipulating a value table.

What is a Match Code ?

Match Code is a tool to help us to search for data records in the system. Match codes are an efficient and user-friendly search aid where key of a record is unknown.

What are the two levels in defining a Match Code ?

Match Code object
Match Code Id.

What is the maximum number of match code Id's that can be defined for one Match code object ?

A match code Id is a one character ID which can be a letter or a number.
Can we define our own Match Code ID's for SAP Match codes ?
Yes, the numbers 0 to 9 are reserved for us to create our own Match Code IDs for a SAP defined Match code object.

What is an Update type with reference to a Match code ID?

If the data in one of the base tables of a match code ID changes, the match code data has to be updated. The update type stipulates when the match code is to be updated and how it is to be done. The update type also specifies which method is to be used for Building match codes . You must specify the update type when you define a match code ID.

What are conversion routines ?

Non standard conversions from display format to sap internal format and vice-versa are implemented with so called conversion routines.

Aggregated Objects

Views, match codes, and lock objects are also called aggregate objects because they are formed from several related tables.

What is a View ?

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 match code 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.

What is database utility ?

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.



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