This section describes the processing of persistent data, that means the data that can be stored outside of an ABAP program. There are three ways you can do this.
The data stored in database tables and files using ABAP programs can be accessed and evaluated independently of the SAP system via the programming interface of the database system and the respective operating system. Data cluster represent a specific ABAP format, which is exclusively understood by ABAP programs.
When external data is changed by application programs, you have to make sure that a consistent state still exists after the changes. This applies especially for editing data on the database.