What is data dictionary?

Question

what is data dictionary?
thank u.

Answer 1

The ABAP Dictionary centrally describes and manages all the data definitions used in the
system. The ABAP Dictionary is completely integrated in the ABAP Development Workbench. All
the other components of the Workbench can actively access the definitions stored in the ABAP
Dictionary.
The ABAP Dictionary supports the definition of user-defined types (data elements, structures and
table types). You can also define the structure of database objects (tables, indexes and views) in
the ABAP Dictionary. These objects can then be automatically created in the database with this
definition. The ABAP Dictionary also provides tools for editing screen fields, for example for
assigning a field an input help (F4 help).
Database objects
Table
DB table
Tools
Screen
Poss. values
F4
Type definitions
Structure
Table type
Data element
The most important object types in the ABAP Dictionary are tables, views, types (data elements,
structures, table types), domains, search helps and lock objects.
BC - ABAP Dictionary SAP AG
ABAP Dictionary
10 December 1999
ABAP Dictionary
Purpose
Data definitions (metadata) are created and managed in the ABAP Dictionary. The ABAP
Dictionary permits a central description of all the data used in the system without redundancies.
New or modified information is automatically provided for all the system components. This
ensures data integrity, data consistency and data security.
You can create the corresponding objects (tables or views) in the underlying relational database
using these data definitions. The ABAP Dictionary therefore describes the logical structure of the
objects used in application development and shows how they are mapped to the underlying
relational database in tables or views.
The ABAP Dictionary also provides standard functions for editing fields on the screen, for
example for assigning a screen field an input help.
What Information is Stored in the ABAP Dictionary?
The most important object types in the ABAP Dictionary are tables, views, types, domains,
search helps and lock objects.
Tables are defined in the ABAP Dictionary independently of the database. A table
having the same structure is then created from this table definition in the underlying database.
Views are logical views on more than one table. The structure of the view is defined in
the ABAP Dictionary. A view on the database can then be created from this structure.
Types are used in ABAP program. The structure of a type can be defined globally in
ABAP programs. Changes to a type automatically take effect in all the programs using the type.
Lock objects are used to synchronize access to the same data by more than one
user. Function modules that can be used in application programs are generated from the
definition of a lock object in the ABAP Dictionary.
Different fields having the same technical type can be combined in domains . A
domain defines the value range of all table fields and structure components that refer to this
domain.
The ABAP Dictionary also contains the information displayed with the F1 and F4 help for a field
in an input template. The documentation about the field is created for a data element
that describes the meaning of the contents of a table field. The list of possible input values that
appears for the input help is created by a foreign key or a search help .
Integration in the ABAP Development Workbench
The ABAP Dictionary is completely integrated in the ABAP Development Workbench. The R/3
System works interpretatively, permitting the ABAP Dictionary to be actively integrated in the
development environment. Instead of the original objects, the interpreters see only internal
representations of these objects.
These internal representations are adjusted automatically when the system finds that changes
have been made in the ABAP Dictionary. This ensures that the screen and ABAP interpreters,
input help, database interface, and development tools always access current data.
SAP AG BC - ABAP Dictionary
ABAP Dictionary
December 1999 11
The following ABAP program lists the airline carriers (see Flight model )
and carrier IDs contained in table SCARR.
DATA: SCARR_TAB TYPE SCARR.
SELECT * INTO SCARR_TAB FROM SCARR.
WRITE: / SCARR_TAB-CARRID, SCARR_TAB-CARRNAME.
ENDSELECT.
Only structure SCARR_TAB is declared in the program. All the information about this
structure, such as the field names, data types and field lengths, are copied from table
SCARR, which is defined in the ABAP Dictionary. This information about table
SCARR is called from the ABAP Dictionary when the program is generated.
This means that the source text of the program need not be adjusted when a change
is made to table SCARR, for example when the length of a table field is changed.
The next time the program is called, the system automatically determines that the
structure of table SCARR has changed. The program is simply regenerated, thereby
retrieving up-to-date information about table SCARR from the ABAP Dictionary.
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ABAP
Interpreter
Dialog
Control Interfaces Screen
Interpreter
ABAP
Tools
Data
Modeler
Screen
Painter
ABAP
Dictionary
When you work on development projects, objects of the ABAP Dictionary can be changed any
number of times before being activated and made available to the operative
components of the system. Objects can have both an active and an inactive version in the ABAP
Dictionary at the same time.
Inactive ABAP Dictionary objects have no effect on the runtime system (ABAP processor,
database interface). This permits greater changes to several objects without impairing the
BC - ABAP Dictionary SAP AG
ABAP Dictionary
12 December 1999
executability of the system. The objects can only be activated together when they have all been
changed.
SAP AG BC - ABAP Dictionary
Tables
December 1999 13
Tables
Tables can be defined independently of the database in the ABAP Dictionary. The fields of the
table are defined with their (database-independent) data types and lengths.
When the table is activated, a physical table definition is created in the database for the table
definition stored in the ABAP Dictionary. The table definition is translated from the ABAP
Dictionary to a definition of the particular database.
Activation
program and
DB UTILITY
T1 T2 T3 ... Tn
T1
T2
T3
Tn
DB
Database-independent Definition of the
Tables in the ABAP Dictionary
Definition of the tables
in the database
A table definition in the ABAP Dictionary contains the following components:
• Table fields define the field names and data types of the fields contained in the
table
• Foreign keys define the relationships between the table and other tables.
• Technical settings control how the table should be created in the database.
• Indexes : To speed up data selection, secondary indexes can be created for
the table
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