For each Business Add-In you have one interface and an adapter class that implements this. The interface is implemented by the user.
The adapter class calls the active implementations.
1. · Filtering
If a Business Add-In is to be executed only under certain conditions, the adapter class ensures that only certain implementations will be executed.
This concept ensures mutlple use. Any Business Add-In that has been implemented once already can be implemented again by those groups listed to the right of the software chain shown in the above graphic.