What are the basic objects in abap dictionary ?

Question

Try to provide the details if anyone knows about it.

Answer 1

The DDIC is nothing but the ABAP Dictionary. The ABAP Dictionary centrally describes and manages all the data definitions used in the system.
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