"I am not too sure what would be examples of requirements for a UI. "
Draw out the screen, on paper the way they want it to look. You don't need fancy expensive software ... I've used Word before using the Insert, Shapes and select the square box and stretch it the way you want ... put the field text above it.
Account Number
Now list the fields and describe what must be done.
(1) Account Number (AcctNum)
20 Alpha-Numeric, Caps Only
Validate 20 chars have been entered
If Account Number is Blank ... Error Message = "Invalid Account Number".
If Account Number entered ... Check database that account number valid ... if Invalid, Error Message = "Invalid Account Number".
do this to what ever other fields are on screen ...
*** IF Valid Account Number Entered ***
(2) Display Account Holder Name, Address, City, Zip
Etc.