Requirement is this way:
1. User will enter basic salary in infotype 8 and click on save button.
2. System will calculate HRA as 50% of basic salary and update infotype 14 across HRA wage type.
3. If there is any change in basic salary then, HRA should be recalculated and to updated in infotype 14 with appropriate start date.
I know the best practice is to have these basic salary dependent allowances in the infotype 8 itself but here the situation is, the employee can ask to stop the payment of HRA or any other allowances at any point of time also they can switch between allowances any time. Hence if we include these wage types in salary structure there would too many changes in infotype 8 (also the WPBP split) hence to avoid this we are planning to store all these allowances in infotype 14.