topic what is data dictionary in Application Development and Automation Discussions

what is data dictionary

Former Member — Wed, 05 Dec 2007 13:02:30 GMT

hi frienrds

i am deva

what is ddic? what is is the purpose of this?

Re: what is data dictionary

Former Member — Thu, 06 Dec 2007 04:38:34 GMT

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.

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 programs. 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.

Reward points if it is usefull ,../..

Girish

Re: what is data dictionary

Former Member — Thu, 06 Dec 2007 04:41:14 GMT

ABAP dictionary is the central repository for creation and management of definitions used in ABAP.

ABAP dictionary is integrated in ABAP workbench and therefore all tools of the workbench like Programs, Screens, function modules can actively access objects defined in data dictionary.

ABAP workbench is an integrated tool for creating an ABAP application.

Type-definitions

Database objects

Services of the dictionary

Functions of the abap dictionary.

The ABAP Dictionary permits a central management of all the data definitions used in the R/3 System without redundancies .

In the ABAP Dictionary you can create user-defined types (data elements, structures and table types) for use in ABAP programs or in interfaces of function modules. Database objects such as tables and database views can also be defined in the ABAP Dictionary and created with this definition in the database.

The ABAP Dictionary also provides a number of services that support program development. This includes

setting and releasing locks(this helps in maintaining the consistency and integrity of data)

defining an input help (F4 help) and

attaching a field help (F1 help) to a screen field are supported.

Type definitions

Analogous to the predefined ABAP types such as C or I , one may define user-defined types in the dictionary.

The following user-defined types are allowed

Data elements: Describe an elementary type by defining the data type, length and possibly decimal places.

Structures: Consist of components that can have any type.

Table types: Describe the structure of an internal table.

Elaboration on the type categories.

There are three different type categories in the ABAP Dictionary:

Data elements (elementary types) Elementary types have no structure. They describe the data type attributes (such as given Dictionary data type, number of places) and information that is relevant for the screen (such as title) of unstructured data objects (variables/fields).

Structures (structured types) Structured types describe the structure and functions of any structured data objects, that is of data structures with components of any type. A component can be a field with an elementary type or can itself be a structure. A table can also be used as a component in a structure. A database table always has a structure and is therefore implicitly a structured type. However, the fields of a database table can only have an elementary type.

Table types Table types describe the structure and functions of internal tables in the ABAP program. Their rows can have any row type. Table types with elementary row type therefore can be defined just the same as multi-dimensional table types (table types with a table type as row type) or table types using structures with table-like components.

Any complex user-defined type may be built using the

previously mentioned basic types.

Database Objects/

Tables and database views can be defined in the ABAP Dictionary.

These objects are created in the underlying database with this definition. Changes in the definition of a table or database view are also automatically made in the database.

Indexes can be defined in the ABAP Dictionary to speed up access to data in a table. These indexes are also created in the database.

Services of ABAP Dictionary

The ABAP Dictionary supports program development with a number of services:

Input helps (F4 helps) for screen fields can be defined with search helps.

Screen fields can easily be assigned a field help (F1 help) by creating documentation for the data element.

An input check that ensures that the values entered are consistent can easily be defined for screen fields using foreign keys.

The ABAP Dictionary provides support when you set and release locks. To do so, you must create lock objects in the ABAP Dictionary. Function modules for setting and releasing locks are automatically generated from these lock objects; these can then be linked into the application program.

The performance when accessing this data can be improved for database objects (tables, views) with buffering settings.

By logging, you can switch on the automatic recording of changes to the table entries.

The ABAP dictionary contains the data definitions (metadata). It is the central information repository for both the application data as well as

the system data. Structures in the dictionary are not only populated with the application( business) data but also the contain system data pertaining to both development and runtime environment.