Use Cases: Questions

Use Case: Questions Key

Revised 7/21/2005

Questions based on Blaha & Rumbaugh, Object-Oriented Modeling and Design with UML, Prentice-Hall, (2nd ed.), 2005 and Larman, Applying UML and Patterns, (3rd ed), Prentice-Hall, 2005.

1. By definition an actor is always external to a system. It may be an object (or a set of objects) that communicates directly with the system but is not part of the system. (p 131 Blaha & Rumbaugh)

2. An actor has a single well-defined purpose. Objects and classes, on the other hand, often combine different purposes. (p 132 Blaha & Rumbaugh)

3. No. An actor can be a anything (or anyone) that communicates directly with the system but is not part of the system. So, another subsystem (or system) could be viewed as an actor. (p 132 Blaha & Rumbaugh)

4. A use case represents "a coherent piece of functionality" that a system provides to one or more actors. You cannot have a use case without an actor. A use case describes the interaction between the system and one or more actors. (p 132 Blaha & Rumbaugh)

5. Grouping normal and abnormal behavior within the same use case "helps to ensure that all the consequences of an interaction are considered together". (p 133 Blaha & Rumbaugh)

6. One example would be a soda machine that only accepts U.S. coins. If the user puts in a Canadian quarter it would not be accepted. The user would probably view this as an error. But the system would simply see this as "another situation to handle". (p 133 Blaha & Rumbaugh)

7. A complete set of use cases can be used to partition the functionality of a system. (p 133 Blaha & Rumbaugh)

8. System-level use cases usually represent functional requirements. They typically do not consider non-functional requirements. (p 134 Blaha & Rumbaugh)

9. Yes. Otherwise the "actor" is not really an actor. (p. 136 Blaha & Rumbaugh)

10. An actor represents "one kind of object for which the system can perform behavior". Obviously this depends on how you define...