DATA DICTIONARY FAQ's
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 as the interface for the runtime environment. It does not generally appear in the ABAP/4 Dictionary.
Q.What is a Data Class?
The Data class determines in which tablespace the table is stored when it is created in the database.
Q. What is a Size Category?
The Size category describes the probable space requirement of the table in the database.
Q. 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 frequently)
- APPL2 - Organisational data (customizing data that is entered when system is configured and then rarely changed)
Read Here at SAP ABAP Forum to Get Answers to More Questions Like Below Given.
Q. What are control tables?
The values specified for the size category and data class are mapped to database-specific values via control tables.
Q. What are the function of the transport system and workbench organiser?
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.
Q. What is a table pool?
Q. 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).
Q. 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).
Q. 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.
Q. 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.
Q. What are the Data types of the external layer?
ACCP, CHAR, CLNT, CUKY,CURR, DATS, DEC, FLTP, INT1,INT2, INT4, LANG, LCHR,LRAW, NUMC, PREC, QUAN,RAW ,TIMS, UNIT, VARC.
Q. 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).
- S: Time stamp YYYYMMDDHHMMSS.
- T: Time of day HHMMSS.
- V: Character string of variable length, length is given in the first two bytes.
- X: Hexadecimal (binary) storage.
Q. 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.
Q.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?
Q.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.
Q.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 a 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.
Q.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 requirements
- table access behaviour
- buffering required
- changes to entries logged
Q.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.
Q.What is the maximum number of structures that can be included in a table or structure?
Q.What are the two methods of modifying SAP standard tables?
- Append Structures and
- Customizing Includes.
Q.What is the difference between a Substructure and an Append Structure?
- In the case of a substructure, the reference originates in the table itself, in the forma of a statement include.
- In thecase of an append structure, the table itself remains unchanged and the reference originates in the append structure.
Q. What are the two ways for restricting the value range for a domain?
- By specifying fixed values.
- By stipulating a value table.
Q.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 the key of a record is unknown.
Q. What are the two levels in defining a Match Code?
- Match Code object
- Match Code Id.
Q.What is the maximum number of match code Id's that can be defined for one Match code object ?
A maximum number of match code Id's that can be defined for one Match code object is36. A match code Id is a one character ID which can be a letter or a number.
Q.Can we define our own Match Code ID's for SAP Matchcodes?
Yes, the numbers 0 to 9 are reserved for us to create our own Match Code IDs for a SAP defined Matchcode object.
Q.What is an Update type with reference to a Match code ID?
If the data in one of the base tables of a matchcode ID changes, the matchcode data has to be updated. The update type stipulates when the matchcode is to be updated and how it is to be done. The update type also specifies which method is to be used for Building matchcodes . You must specify the update type when you define a matchcode ID.
Q.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, matchcodes, and lock objects are also called aggregate objects because they are formed from several related tables.
Q.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 of being derived from one or more tables. A view can be used to summarize data which is distributed among several tables
Q.How many types of Views are there ?
1)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.
2) 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.
3) 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.
4) 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.
Q.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.
Q.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.
Q. 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.
Q.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.
Q. What are subroutines?
Subroutines are program modules which can be called from other ABAP/4 programs or within the same program.
Q. 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.
Q. 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.
Q. 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.
Q. 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.
Q. What is the difference between the function module and a normal ABAP/4 subroutine?
In contrast to normal subroutines function modules have uniquely defined interface. Subroutines do not return values.
Subroutines do not return exceptions. Subroutines cannot be tested independently. Declaring data as common parts is not possible for function modules. Function modules are stored in a central library.
Q.What is a function group?
A function group is a collection of logically related modules that share global data with each other. All the modules in the group are included in the same main program. When an ABAP/4 program contains a CALL FUNCTION statement, the system loads the entire function group in with the program code at runtime. Every function module belongs to a function group.
Q.What is the difference between internal tables and extract datasets?
A. The lines of an internal table always have the same structure. By using extract datasets, you can handle groups of data with different structure and get statistical figures from the grouped data.
B. You have to define the structure of the internal table at the beginning. You need not define the structure of the extract dataset.
C. In contrast to internal tables, the system partly compresses extract datasets when storing them. This reduces the storage space required.
D. Internal tables require special work area for interface whereas extract datasets do not need a special work area for the interface.
Read more here SAP ABAP Dictionary Concepts