5 Use Case Analysis

Use Cases

A use case is a set of activities that produce some output result. Each use case describes how the system reacts to an event that triggers the system.

Or, a use case is a set of end-to-end activities that start with a trigger event and continues through many possible paths until some output has been produced, and the system is at rest again.

The assumption in this event-driven model is that everything in the system is a response to some trigger event. When there are no events, the system is at rest, waiting for the next event to trigger it.

Elements of a Use Case

• Basic Information -- name, number, brief description; trigger (external or temporal)

It is helpful to have a consistent viewpoint when writing use cases

• Inputs and Outputs (also called data flows) -- along with their sources and destinations respectively

• Details -- of individual steps within the use case and the input and outputs they use; the steps are listing in the order in which they are performed and and any conditional steps are clearly noted

Building Use Cases

• Identify the Major Use Cases
  • If we discover more than 8 or 9 use cases, this suggests that the system is complex (or that the use cases are not defined at the right level of detail). If there are really more than 8 or 9 use cases, we can group them into packages or related use cases
• Identify the Major Steps for Each Use Case
  • the steps should focus on what the business process or system does to complete the use case, as opposed to what actions the users or other external entities do
  • the steps should be listed in the order in which they are performed (though there may be steps that are performed only occasionally, have no formal sequence in which they are done, or loop back and forth)
  • each step should be about the same size (e.g. "enter first line item" is not the same size as "balance the account")
• Identify Elements within Steps
  • delve more deeply into the steps within the use case to understand and describe their inputs and outputs; each step should have at least one input and at least one output
• Confirm the Use Case
  • one approach: ask the user to role-play, or execute the use cases using the steps in the use case

 

Use case/Scenario name:			ID No:
Short description:
Trigger:
Type: External or Temporal
Major Inputs:		Major Outputs:
Description	Source	Description	Destination
Major Steps Performed			Information for Steps

 

Applying the Concepts at CD Collection, p. 150 Dennis & Wixom.