As discussed in Data Types and Data Objects section, Data Dictionary is one of the methods to create Data Types by creating data definitions, namely metadata(data element,structure,table type and type groups). Besides this main role it also works as a Data Access Layer(DAL) by presenting Database Tables. Data Dictionary provides better classification, consistency, security and reusability of data. Data Dictionary can be maintained either from SE11 or from SE80 and also can be displayed from SE84 which is a universal repository. Before Eclipse and HANA releases, there were nine types of ABAP Data Dictionary Objects. With HANA and Eclipse support there are new types like CDS types and Database Procedure Proxy.
Below classical Data Dictionary Objects and their usage are examined. Further explanation and samples are presented in each object’s page.
Tables are defined in the ABAP Dictionary independently of the database. From this table definition follows the creation of a table with the same structure in the underlying database.
Views are logical views of more than one table. The structure of the view is defined in the ABAP Dictionary. A view of the database can then be created from this structure.
Structure fields, table fields and Data Objects in ABAP programs refer to Data elements which is one of Data Types in ABAP. Data elements also have own attributes like linking search help, short/middle/long texts etc.
Stucture is a collection of fields. These fields can be collected in flat, nested or deep structure style.Structures types can be seen in following figure.
A table type describes the structure and functional attributes of an internal table in ABAP.The row type can be one of data element, structure, another table type or can be a reference type.
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. This method helps to define Dictionary objects by ABAP coding.
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.
Search Helps provide field values for screen elements. F4 keyboard pushbutton activates Search Helps for screen fields.
These 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.