- Use Case Definition.

Use Cases define how the users interact with the system.

A Use Case must be specified         as                     One Thing       (Operation to be done on the computer)

               done by          One Actor        (Person or another computer)

               in                      One Place        (On the same computer)

               at                      One Time.        (as part of a single operation)

A practical criteria of when a main use case is complete is to ask your self "Is now a good time to go for a pee?" Of course you could go for a coffee, lunch, a meeting or home, but the above concept sets a minimum break that most users would accept.

When you come to define the use case, you need to write a brief description (3 pages = absolute maximum, including diagram). It should reflect the following details (based on simplistic expressions as suggested):

All use cases must have an           Objective

                  "As a 'cusomer,' -------" (Actor)

                  "------- I wish to place an order for the collection and delivery of a package ---" (The thing)

                  "------- so that I can arrange deliveries without assistance from the delivery company." (A condition)


All use cases must have                  Pre-conditions and at least one 'trigger'.       

                  "The user must know, the collection address and the delivery address" (Precondition)

                  "Details of availability to collect and the minimum travel time required" (Precondition)

                  "Full details of the package; size, contents, weight, special  features (poisonus, fragile etc)" (Precondition)

                  "This data must be entered into the computer and the 'I accept' button must be pressed" (Trigger)

All use cases must have                  Post-conditions and and criteria for success.

                  "The order must be acknowledged on the computer as having one of three criteria:  



                                                               Conditional failure; try again. 


NOTICE: All references to a computer are single statements. There are NO descriptions of what the computer does.