Discussion

Using the diagram, explicitly ask yourself the following questions:

• Is there an actor representing every kind of user who will use the system?
• Is there a system actor for every legacy system with which this system needs to comminuate?
• Can each actor do everything they need to do using only the use cases they are related to?
• Are any obvious use cases missing? For example, use case models are often symmetric: if there are use cases for creating bookings, printing booking receipts, printing performance receipts, and cancelling performances, perhaps there should also be use cases for cancelling bookings and creating performances.

Unless you are on a small system (if you have not more than 15-20 use cases) draw one use case diagram for each actor (or for a few related actors), rather than one diagram for the whole system.