Visibility Rules in Subpackages 

Nested packages have a special relation between packages and their subpackages that also comes along with a restriction of visibility. As a general rule, the visibility has a one-way effect, namely from top (surrounding package) to the bottom (subpackages).

This means that elements in sub packages are always visible and accessible within their surrounding package (see graphic on the left).

However, the elements of the surrounding package are always invisible (and therefore not accessible) in embedded packages (see graphic on the right). For instance, it is not allowed for an ABAP program in the subpackage P2_1 to call a function module or so from the package P1. 

 

 

This behaviour is analogous to the layering principles of the software components. A higher-level software component can always use development objects from a lower-level software component, but never the other way round. For instance, in SAP ERP this principle entails that development objects from the SAP_BASIS are not allowed to access the application’s layer SAP_APPL. In the reverse direction however, it is always granted for the applications components to use the SAP_BASIS functionality.

 

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