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, the system creates a physical table definition in the database for the table definition stored in the ABAP Dictionary. The system translates the table definition from the ABAP Dictionary to a definition of the particular database. You can see these relations between the ABAP Dictionary and the database in the following figure.
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 the creation of the table in the database.
To speed up data selection, secondary indexes can be created for the table.
The customer can modify SAP tables with append structures and customizing includes . This kind of modification ensures that the customer enhancements are automatically merged with the new versions of the SAP tables when there is a release upgrade.