神马文学网UML 2 Use Case Diagramming Guidelines
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use case diagram is 揳 diagram that shows the relationships among actors and use cases within a system.? Use case diagrams are often used to:
- Provide an overview of all or part of the usage requirements for a system or organization in the form of an essential model or a business model
- Communicate the scope of a development project
- Model your analysis of your usage requirements in the form of a system use case model
A use case model is comprised of one or more use case diagrams and anysupporting documentation such as use case specifications and actor definitions. Within most use case models the use case specifications tend to be the primaryartifact with use case diagrams filling a supporting role as the 揼lue? thatkeeps your requirements model together. Use case models should bedeveloped from the point of view of your project stakeholders and not from the(often technical) point of view of developers. There are guidelines for:
- Use Cases
- Actors
- Relationships
- System Boundary Boxes
1. Use Cases
A use case describes a sequence of actions that provide ameasurable value to an actor. A usecase is drawn as a horizontal ellipse on a UML use case diagram, as you see in Figure 1.
- Use Case Names Begin With a Strong Verb
- Name Use Cases Using Domain Terminology
- Place Your Primary Use Cases In The Top-Left Corner Of The Diagram
- Imply Timing Considerations By Stacking Use Cases. As you see in Figure 1, the use cases that typically occur first are shown above those that appear later.
Figure 1. Implying timing considerations between usecases.
2. Actors
An actor is a person, organization, or external system thatplays a role in one or more interactions with your system (actors are typically drawn asstick figures on UML Use Case diagrams).
Figure 2. Online shopping.
- Place Your Primary Actor(S) In The Top-Left Corner Of The Diagram
- Draw Actors To The Outside Of A Use Case Diagram
- Name Actors With Singular, Business-Relevant Nouns
- Associate Each Actor With One Or More Use Cases
- Actors Model Roles, Not Positions
- Use <
> to Indicate System Actors - Actors Don抰 Interact With One Another
- Introduce an Actor Called 揟ime? to Initiate Scheduled Events
3. Relationships
There are several types of relationships that may appear ona use case diagram:
- An association between an actor and a use case
- An association between two use cases
- A generalization between two actors
- A generalization between two use cases
Associations are depicted as lines connecting two modelingelements with an optional open-headed arrowhead on one end of the lineindicating the direction of the initial invocation of the relationship.Generalizations are depicted as a close-headed arrow with the arrow pointingtowards the more general modeling element.
Figure 3. Enrolling students in a university.
- Indicate An Association Between An Actor And A Use Case If The Actor Appears Within The Use Case Logic
- Avoid Arrowheads On Actor-Use Case Relationships
- Apply <
> When You Know Exactly When To Invoke The Use Case - Apply <
> When A Use Case May Be Invoked Across Several Use Case Steps - Introduce <
> associations sparingly - Generalize Use Cases When a Single Condition Results In Significantly New Business Logic
- Do Not Apply <
>, < >, or < > - Avoid More Than Two Levels Of Use Case Associations
- Place An Included Use Case To The Right Of The Invoking Use Case
- Place An Extending Use Case Below The Parent Use Case
- Apply the 揑s Like? Rule to Use Case Generalization
- Place an Inheriting Use Case Below The Base Use Case
- Apply the 揑s Like? Rule to Actor Inheritance
- Place an Inheriting Actor Below the Parent Actor
4. System Boundary Boxes
The rectangle around the use cases is called the systemboundary box and as the name suggests it indicates the scope of your system ?the use cases inside the rectangle represent the functionality that you intendto implement.
- Indicate Release Scope with a System Boundary Box. In Figure 2 you see that three system boundary boxes are included, each of which has a label indicating which release the various use cases have been assigned to.
- Avoid Meaningless System Boundary Boxes.
5. Recommended Resources
- Are You Ready For the MDA?
- Be Realistic About the UML
- Essential/Abstract Use Case
- Examining The Model Driven Architecture (MDA)
- Introduction to the Diagrams of UML 2
- Introduction to Object Orientation (OO) and UML
- Introduction to UML 2 Use Case Diagrams
- Modeling Style Guidelines
- Pavel Hruby's UML 2.0 Stencil for Visio
- Roadmap for Agile MDA
- System Use Case
- Use Case Template: Formal
- Use Case Template: Simple
- Why Extend the UML Beyond Object and Component Technology?
- XP and the UML?
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