Use Case Modeling

Watch the video on use cases Review at minute 2:41-3:37

Use Cases are one way to capture requirements A visual way to capture functional requirements Each bubble is a discrete user goal Actors can be people, or external systems Each bubble is mapped to a textual description

Use Case Description See example on class schedule Include basic and alternate/exception flows – Each alternate flow must start at a step in the basic flow, and may return to a step in the basic flow – Exception flows are analogous to exceptions in code Includes versus preconditions Do not use language that hints at implementation details or system interactions – Avoid click, press, type, button, etc. – Unnecessarily limits creativity

Use Case Diagrams Made up of three components – Actors (people or external systems) – Use Cases (with textual descriptions) – Relationships Authorized Staff Worker Teacher Student Record class gradesReview Transcripts

First, identify actors Who or what will provide input to the system? Who or what will need output from the system? Exercise: identify three actors for an ATM

Answer: identify three actors for an ATM Customer Database (for account information, etc) – this is an external system Maintenance person

Relationships between actors One can be a specialization of another Actors are classes, not individual people Student Graduate Student

Next, identify user goals User Goals are statements that represent what the users need to accomplish, independent of specific software features – “Buy a book” – “Return a book” – “View order history” – “Record a log for a transaction” Exercise: identify five uses cases for an ATM

Answer: identify five use cases for an ATM Authenticate user Withdraw funds Deposit funds Check balance Transfer funds Load bills etc Each would be a bubble in diagram

Finally, add relationships Three types of relationships for use cases: Includes Extends Generalization

Includes relationship One use case can invoke the behavior of another – arrow goes toward included use case Not always, but often a precursor – I.e. the “Buy a book” use case includes the “Authenticate customer” Teacher Alter Student Grade Record Grades for a Section >

Extends Relationship Similar to the includes, but used for handling an abnormal situation – arrow goes toward extended use case Authorized Staff Worker Alter Student Grade Alter student grade for a class taken more than a year ago >

Generalization Relationship Replaces generic functionality with an concrete implementation – arrow goes toward extended use case User Authenticate user Authenticate by card swipe Authenticate by iris scan

Why Use Cases? Visual representation easy to understand Relationships are opportunities for reuse Use case descriptions can be basis for testing Can be the basis for planning and scheduling

Quiz review What is a single use case? What is a use case description? What is a use case diagram? What is an actor? What is a relation? – includes relation? – extends relation? – generalization relation? – which way does the arrow go?

In-class Exercises Complete the ATM use case diagram – use each type of relation at least once Complete the use case description for the Withdraw Funds use case for the ATM Complete the exercises at: Due at beginning of next class

In-class Exercises (time permitting) Examine the Quiz Game description In your teams, come up with at least seven use cases; – At least three actors – At least one of each type of relationship – Complete a use case description for each use case Turn in this assignment through svn – See instructions, rubric, and details on project page