Lecture 06
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The document describes use cases and their components. It provides an example use case for deleting information that has components like name, priority, actors, and a normal course of events description. It also includes alternative paths and exceptions. Finally, it discusses some limitations of use cases like not capturing non-functional requirements around usability, reliability, performance, portability, and access.
Lecture 06
- 1. Lecture 06
- 2. The UML allows us to extend and reuse already defined use cases by defining the relationship among them. Use cases can be reused and extended in two different fashions: extends and uses. Relationship among Use Cases
- 3. Reuse and Extension An Example
- 5. An elaborated use case has the following components: Priority: the relative implementation priority of the use case. Actors: names of the actors that use this use case. Summary: a brief description of the use case. Precondition: the condition that must be met before the use case can be invoked. Post-Condition: the state of the system after completion of the use case. Extend: the use case it extends, if any. Includes: the use case it uses, if any. Normal Course of Events: sequence of actions in the case of normal use. Alternative Path: deviations from the normal course. Exception: course of action in the case of some exceptional condition. Assumption: all the assumptions that have been taken for this use case. Describing a Use Cases
- 6. Use Case Name: Delete Information Priority: 3 Actors: User Summary: Deleting information allows the user to permanently remove information from the system. Deleting information is only possible when the information has not been used in the system. Use Case Example Delete Information
- 7. Preconditions: Information was previously saved to the system and a user needs to permanently delete the information. Post-Conditions: The information is no longer available anywhere in the system. Includes: Record Transactions, Cancel Action Extends: None Normal Course of Events: 1. The use case starts when the user wants to delete an entire set of information such as a user, commission plan, or group. 2. The user selects the set of information that he/she would like to delete and directs the system to delete the information. Exception 1, 2 3. The system responds by asking the user to confirm deleting the information. 4. The user confirms deletion. Alternative Path: Cancel Action 5. A system responds by deleting the information and notifying the user that the information was deleted from the system. 6. Uses: Record Transaction 7. This use case ends. Use Case Example Delete Information
- 8. Alternative Path - The user does not confirm Deletion 1. If the user does not confirm deletion, the information does not delete. 2. Uses: Cancel Action Exceptions: 1. The system will not allow a user to delete information that is being used in the system. 2. The system will not allow a user to delete another user that has subordinates. Assumptions: 1. Deleting information covers a permanent deletion of an entire set of data such as a commission plan, user, group etc. Deleting a portion of an entire set constitutes modifying the set of data. 2. Deleted information is not retained in the system. 3. A user can only delete information that has not been used in the system. Use Case Example Delete Information
- 10. Usability Color blind people should not have any difficulty in using the system – color coding should take care of common forms of color blindness. Reliability The system needs to support 7 x 24 operation Performance Authorization should be completed within 1 minute 90% of the time. Average authorization confirmation time should not exceed 30 seconds. Portability The system should run on Windows 98 and above as well as Sun Solaris 7.0 and above. Access System should be accessible over the internet – hidden requirement – security Because of this shortcoming, use cases must be augmented by additional information. Limitations of Use Cases