1. L16 Scenarios and Use cases

2. Topics Scenarios Use cases Sequence diagrams Use cases in analysis Tutorial work

3. situation GetUHome’ is a company which provides a breakdown service to its members nationwide. Members pay a yearly subscription to the company. In the event of a breakdown, the distressed motorist phones the call centre where an available operator takes the call. The operator checks that the caller is a paid-up member. If he is, the operator obtains details of the motorist’s problems and location. He then finds the most appropriate rescue vehicle to deal with the problem and calls the rescue driver. The rescue driver proceeds to the location of the motorist and the operator reports the expected arrival time to the motorist.

4. Identify scenarios Pay Subscription’ use case ‘Call for Help’ use case

5. Concrete Scenario A concrete scenario is described in terms of specific instances, that is not just 'an operator' but 'Paul, a 2nd Year business studies student who works part time at GetUHome to finance his studies and clubbing'. The scenario describes a concrete use of the proposed system. The story describes exactly what happened, not several possible outcomes.

6. Use case Diagram Call for Help MotoristOperator Rescue driver

7. Extensions Symbols Use case matrix Extends and Uses –Uses – a smaller unit of functionality which is used by several larger units – e.g. check member info –Extends – variations to use cases require additional behaviour in special cases – these ‘extend’ the original use case

8. Sequence diagram motoristoperatorRescue driver Call for help Request member info Member info Check member Request location & problem Location and problem Request OK and ETA OK and ETA ETA Vehicle proceeds to location Select appropriate vehicle

9. Use cases in analysis Information Requirements · What information is required to identify a member? · What information is required to identify the problem and location? · How do we choose the most appropriate vehicle to send? · Who provides the ETA? The operator, the rescue driver or both in consultation? How is it calculated? Variations · What happens if the membership has expired? · What happens if the motorist can’t remember his id? · What if the motorist has ‘borrowed’ someone else’s id? · What if the motorist doesn’t know where they are? · How does the rescue driver find the motorist? Performance · What is an acceptable time to wait for an operator? · What is an acceptable time to wait for a rescue vehicle

10. Mis-use cases Identify –Treats and attacks Attempt to acquire customer list –Deliberate misuse by humans Use of a stolen membership card

11. Design and use-cases Concrete Scenarios –Write a concrete scenario for each use case to flesh it out Brain storming –One group identify problems with scenario –Other group suggest solutions Role playing –Testing out a proposed solution using role playing

12. Issues Managing large numbers of use cases Integrating into the development process Scope of use-case – often at the level of an interaction over a small period of time – what about the long-running processes with the scope of the whole period of membership? Tutorial – application to one added functionality to the CSM WBIS or your own suggested functionality