CS 325: Software Engineering February 3, 2015 Deriving Use Cases from Requirements Actors and Use Cases Creating A Use Case Diagram Complex Use Case Diagrams

Actors and Use Cases CS 325 February 3, 2015 Page 59 In a software system model, an actor is a role played by one of the system’s stakeholders who interacts with the system. A use case is a business process that begins and ends with the actor and that accomplishes a business task for that actor. For example, for a software system that tests the effectiveness of a spam filter, one actor might be a system administrator who is responsible for ensuring that spam messages are blocked from the mailboxes of employees. Among the use cases for this actor: Testing how effectively a filter blocks spam Testing how effectively a filter permits “ham” Determining proper spam probabilities for blocking messages

Actors and Use Cases CS 325 February 3, 2015 Page 60 Other actors who might interact with the spam filter tester: The developer of a spam filter dictionary, who might need to determine the effectiveness of a dictionary in blocking spam messages and not blocking ham messages. A commercial developer, who might use the tester to determine whether the particular phrasing of a message would cause it to be blocked as spam.

Creating A Use Case Diagram CS 325 February 3, 2015 Page 61 Start with the system boundary and the actors. Insert the use cases and the associations. Note any extensions, inclusions, and generalizations.

Creating A Use Case Diagram CS 325 February 3, 2015 Page 62 Consider a student information system (SIS) with the following features: Student enrollment tools for online registration, class schedule checking, course cancellation notification, wait listing for full classes, submitting transfer credits Academic advising support tools for degree auditing, transfer credit equivalencies, prerequisite checking, course requirement overrides Faculty tools for generating class rosters, recording course grades, posting new assignments, retrieving laboratory grades Administrative tools for enrollment analysis, classroom scheduling, awarding financial aid, inclement weather notifications

Creating A Use Case Diagram CS 325 February 3, 2015 Page 63

Complex Use Case Diagrams CS 325 February 3, 2015 Page 64 The whole point of a use case diagram is to clarify the development team’s understanding of the requirements of the planned system. An overly complicated diagram may obscure that understanding rather than clarifying it.

Complex Use Case Diagrams CS 325 February 3, 2015 Page 65 Splitting the diagram into multiple diagrams, in this case representing smaller subsystems, improves their overall clarity. Also note how the use of the inclusion relationship eliminates potentially confusing redundancies.