As we are moving to Fiori first yet cloud ready approach for any development, why restrict us to GGB0 or GGB1 for creating validation or substitution rules?
We can utilize the Fiori application - Manage Substitution and Validation Rules to create the rules which will be applied to all the standard processes such as standard interfaces, GUI T-codes and managing standard processes in custom program.
In this blog, we will create a custom-defined function in the validation rule on asset creation or modification done through the Fiori app - ‘Manage Fixed Assets’. The rule will validate against the supplier assigned to the asset master record.