In a library system, the user wants to borrow a book. The user enters the ID. The system checks the Users database to verify this is an authentic user. The due date is calculated and entered into the BooksDue database. We will first construct the decision table, then daw the DFD for the BorrowBook function. The decision table corresponds to one or more IC cards, where Y or N indicates Yes or No, and X the corresponding action to be taken.

Decision Table:
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  New user?                 Y

  Authentic user?                Y

______________
  Ask user to enter ID      X
  and verify against
  Users database.

  Calculate due date             X
  and enter into
  BooksDue database.
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