George Wang, Ph.D. COMP 380/L Lesson 2

Use Case Use cases are a way to capture system functionalities (i.e., functional requirements) Based on use case diagrams and their associated user case descriptions, – The rest of UML diagrams are developed. – The functions of software products are tested. Components – Diagrams – Descriptions 2

Use Case Diagrams / Descriptions Use case diagrams show use cases, actors and relations among them. Use case descriptions address in details what the system (software product) shall do for the actor to achieve a particular goal (functionality). 3

Use Case Development Process 1.Find actors and use cases, and draw a draft of a use case diagram – GUI might be helpful for identifying interfaces between user(s) and the system, which initiate functions (use cases) 2.Refine iteratively a use case diagram by considering relationships between use cases and actors, and between use cases, and between actors 3.Develop each use case (starting with the priority ones) by creating its use description 4

Use Case Tutorial - Use Cases Represent a distinct functionality for a system Each use case must have a name describing the function Use an oval with the name of the use case 5

Use Case Tutorial - Actors A use case must be initiated by someone or something outside the scope of the use case An actor does not need to be a human user; any external system or element outside of the use case may trigger the use case An actor can be shown with a stick figure with the name of the actor written near the icon 6

Use Case Tutorial - Relationships An actor is associated with one or more use cases A relationship between an actor and a use case indicates the actor initiates the use case, the use case provides the actor with results An association is shown as a solid line between an actor and a use case Other types of relationships – Actor and use case generalization – Use case include – Use case extend – topic=/com.ibm.xtools.modeler.doc/topics/crelsme_ucd.html 7

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Use Case Descriptions Use case name (with use case ID) Characteristic information (description, scenario, trigger event, actors, related use cases, stakeholders, pre-condition, post-condition) Main (primary) scenario (“normal” messages flows between an actor and a use case) Alternative scenario (“exceptional” or “conditional” workflows between an actor and a use case) 10

Use Case Description - Template

Use Case Description - Example