How to Create Use Case Diagrams
A use case diagram is a graphical description of the different ways users interact with a system. These diagrams are useful tools for communicating how a system must operate with project stakeholders, designers and developers. They are simple drawings primarily composed of subjects, actors, use cases and associations between the actors and the use cases. Use case diagrams should document an observable and valuable outcome for users of the system.
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Instructions
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Conduct user research or study user research reports to learn about the people who will use your system and their needs. Observe potential users in their environment and ask questions about the tasks they must accomplish with the current or proposed system.
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Gather your notes and drawing tools. You can use simple materials, such as pen and paper. If you are building the use case diagrams as a team or in a brainstorming sessions, use a whiteboard. For final documentation use software with flow-chart graphics, such as Microsoft PowerPoint or Microsoft Visio.
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Draw a rectangle to represent the subject. The subject is the system or subsystem that is being developed or enhanced. "E-Commerce Website" is an example of a subject. Write the name of the subject in the upper corner. The subject also acts as the system boundary within the diagram, with actors depicted on the outside and use cases depicted on the inside.
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Document the use cases. Separate each one, draw an ellipse around it and place it inside the applicable subject rectangle. Each use case represents a single task that the system must carry out. "Buy a Product" is an example use case for the subject "E-Commerce Website." Some use cases may be part of an extended task represented in another use case. For example, in order to buy a product, the shipping address must be validated.
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Draw the actors. An actor uses the system via the use case to complete a single task. "Website Visitor" is an example of an actor. Draw one stick figure per actor and place it outside the subject rectangle. While it most commonly represents a person, an actor is anything that uses the system to complete a task. If the actor is not a person, you can use a more fitting icon to represent the actor. Recall the user research and consider the set of use cases that an actor could be associated with. Align the actors in your diagram so they are closest to their associated use cases.
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Draw the associations. The association indicates which actors interact via which use cases to complete their tasks. Draw a solid line to represent an association whenever an actor is involved with a use case. Use an arrowhead on one end of the line to illustrate the direction of the relationship or to show a primary actor relationship with the use case.
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Tips & Warnings
When drawing associations, arrowheads are often confused with data flow so avoid them unless it is necessary for your diagram.
