UML Use Case Diagrams How use cases relate to one another
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UML Use Case Diagrams How use cases relate to one another
A use case diagram shows all use cases and their relationships with one another and all actors
Use case diagram = use cases + actors + relationships ¡ Actor = an external entity that might interact with
our system ¡ To create a use case diagram, we
1. define the system 2. find the actors 3. find the use cases 4. define the relationships between them
An example of a use-case diagram
Insurance Salesperson
Customer
Sign an insurance policy
Sales statistics
Customer statistics
Actor Use case
System box
An actor is an external thing interacting with the system
Insurance Claims System
Claimant
Claims Rep
Billing System
Agent
Manage Claim
Claimant
Claims Rep
Payment System
Agent Review Claim
Status
Use cases are activities that the system does for the actors
Example: Simple Order Entry System
Customer
Browse Products & Place Orders
Allows a customer to browse through a product catalog and
place orders for items
A person who may acquire products
Credit Institution
An organization that provides credit on
demand to customers
Use brainstorming to find your initial set of actors ¡ You'll find most of your actors in a brainstorming
session ¡ Then start your use case development ¡ Other actors will reveal themselves as you realize
the use cases
Brainstorming questions help to find actors ¡ Who starts and stops the system? ¡ Who does user and security management? ¡ Who does system administration? ¡ Is the system automated via cron? If so, time is an actor ¡ Is there a monitoring process that restarts the system if it fails? ¡ How are software updates handled? ¡ Who evaluates system activity or performance? ¡ Who will use the main functionality of the system? ¡ Who will need support from the system to do their daily tasks? ¡ Who will need to administrate and keep the system working? ¡ Which hardware devices does the system need to handle? ¡ With which other systems does the system need to interact? ¡ Who or what cares about the results that the system produces?
Primary actors start an activity
Secondary actors merely get value from the system
Conclusion ¡ The use case diagram gives us a high-level view
of all of the use cases, the actors, and how they relate among themselves
¡ You'll find your initial set of use cases based on the functional requirements
¡ You'll find your initial set of actors by brainstorming
¡ As you analyze further, more use cases and actors will reveal themselves
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