What is the use of Datadictionary.

[Former Member]

Hi Experts,

1) Why SAP People designed datadictionary. What is the main reason SAP People put data dictionary in Application server. As per my knowledge it will reduce the burden and no.of strips to database. Is there any other reasons?.Pease clarify.

2)If i have a table with some data. I need to change In domain level datatype and length it gives error . How can i overcome it.

Regards

Pratap.M

[Former Member]

hi meda,

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 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.

<b>Hope this is helpful, Do reward</b>

[Former Member]

Data types

Data types are the actual type definitions in the ABAP Dictionary. They allow you to define elementary types, reference types, and complex types that are visible globally in the system. The data types of database tables are a subset of all possible types, namely flat structures.

Data Elements

Data elements in the ABAP Dictionary describe individual fields. They are the smallest indivisible units of the complex types described below, and are used to specify the types of columns in the database. Data elements can be elementary types or reference types.

Structures

A structure is a sequence of any other data types from the ABAP Dictionary, that is, data elements, structures, table types, or database tables. When you create a structure in the ABAP Dictionary, each component must have a name and a data type. In an ABAP program, you can use the TYPE addition to refer directly to a structure.

If you define a local data type in a program by referring to a structure as follows:

TYPES <t> TYPE <structure>.

Table Types

Table types are construction blueprints for internal tables that are stored in the ABAP Dictionary.

When you create a table type in the ABAP Dictionary, you specify the line type, access type, and key. The line type can be any data type from the ABAP Dictionary, that is, a data element, a structure, a table type, or the type of a database table. You can also enter a predefined Dictionary type directly as the line type, in the same way that you can with a domain.

Type Groups

Before Release 4.5A, it was not possible to define standalone types in the ABAP Dictionary to which you could refer using a TYPE addition in an ABAP program. It was only possible to refer SAP AG BC - ABAP Programming

Data Types in the ABAP Dictionary to flat structures. Structures in programs corresponded to the structures of database tables or structures in the ABAP Dictionary. In ABAP programs, you could only refer to database tables and structures in the ABAP Dictionary using LIKE. It was, however, possible to refer to individual components of the Dictionary type. Complex local data types such as internal tables or deep structures had no equivalent in the ABAP Dictionary. The solution to this from Release 3.0 onwards was to use type groups. Type groups were based on the include technique, and allowed you to store any type definitions globally in the Dictionary by defining them using TYPES statements.

Views:

There are 4 types views are avilable in SAP.

Database View - To club more than one table

Projection View - To hide fields in one table

Maintanance View - To maintain database records in table

Help View - To provide help for a fields (Same functionality as Search help. This is outdated)

View are improves perfromance in the following aspects

1. If you want to use more than two table in 'JOIN' condition better to use Views . It will improves performance of a program

2. If you want to use mutiple FOR ALL ENTRIES clause, better to club all SELECT statement in a view.

Lock Objects:

Lock objects are use in SAP to avoid the inconsistancy at the time of data is being insert/change into database.

SAP Provide three type of Lock objects.

- Read Lock(Shared Locked)

protects read access to an object. The read lock allows other transactions read access but not write access to

the locked area of the table

- Write Lock(exclusive lock)

protects write access to an object. The write lock allows other transactions neither read nor write access to

the locked area of the table.

- Enhanced write lock (exclusive lock without cumulating)

works like a write lock except that the enhanced write lock also protects from further accesses from the

same transaction.

You can create a lock on a object of SAP thorugh transaction SE11 and enter any meaningful name start with EZ Example EZTEST_LOCK.

Use: you can see in almost all transaction when you are open an object in Change mode SAP could not allow to any other user to open the same object in change mode.

Example: in HR when we are enter a personal number in master data maintainance screen SAP can't allow to any other user to use same personal number for changes.

Technicaly:

When you create a lock object System automatically creat two function module.

1. ENQUEUE_<Lockobject name>. to insert the object in a queue.

2. DEQUEUE_<Lockobject name>. To remove the object is being queued through above FM.

You have to use these function module in your program.

Search Helps:

These are two types.

Elementary n Collective.

1) Elementary search helps describe a search path. The elementary search help must define where the data of the hit list should be read from (selection method), how the exchange of values between the screen template and selection method is implemented (interface of the search help) and how the online input help should be defined (online behavior of the search help).

2) Collective search helps combine several elementary search helps. A collective search help thus can offer several alternative search paths.

3)An elementary search help defines the standard flow of an input help.

4) A collective search help combines several elementary search helps. The user can thus choose one of several alternative search paths with a collective search help.

5)A collective search help comprises several elementary search helps. It combines all the search paths that are meaningful for a field.

6)Both elementary search helps and other search helps can be included in a collective search help. If other collective search helps are contained in a collective search help, they are expanded to the level of the elementary search helps when the input help is called.

See the below link to understand this completely:

http://help.sap.com/saphelp_nw2004s/helpdata/en/cf/21ee93446011d189700000e8322d00/frameset.htm

Rewards if useful.

[Former Member]

hi,

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 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 useful..

[Former Member]

Hi

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.

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.

<b>Type definitions</b>

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.

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.

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.