I'm working on a rewrite of a current application. I'm using the use case diagrams and specifications to capture the requirements. I've a scenario where the actor keys in details to the system and the validation and processing(Lot of business rules) of those details are happening in the cobol modules in the backend. The results are given to the actor and he keys in the credit card details. That is again authorised / validated in the backend.
I would like to know how to represent the backend processes in the use case diagram. The question is should it be represented in Use Case diagram or not?
Anyways I'll be having all the rules listed out in my Use Case Specification under Special Requirements.