suppose we need a human resource management system. mostly use our imagination to see what info is needed in the real life. for eg each person has name add phone email each person has payroll info, position, manager there are dept dept hiearchy employment type start end date project project hierchy budget performance eval per year and anything you can think of the above is just the data layer. now consider app layer what use case you would need and make them as stored procedures
things can make a little complicated for instance a manager can check the salary of his team or sub team, but if people move up and down or move in or out of the team from time to time, the mngr can only check when the person is in his team.