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