Domain is the encapsulator ABAP variable types and also plays a role for creating Data Element with assignment in Data Type tab. If you will not use Elementary Types while doing Data Type assignment , then you have to use Domains. Besides Domains hold three type of information
- Conversion Routine
ABAP types can have two formats whose first is internal(input) format and second is external(output) format. Conversion field with the related function modules determine how conversion will take place
- Fixed Values or Interval Values
As a very common usage Listbox values in a screen field comes from these fixed values. It contains value/desciption pairs. Another usage is defining date intervals with domains thanks to interval values feature.
- Value Table
This feature is very crucial while constituting relations between different tables. Database table or structure fields make use of this feature while creating search helps,check tables or primary assignments.