Analysis: Use Case Descriptions

Section 0: Module Objectives or Competencies

Section 1: Use Case Descriptions

The behavior of a use case can be described by means of activity diagrams and state diagrams, interaction diagrams (sequence and communication diagrams), as well as textual use cases, where appropriate.

A use case description is a written account of the sequence of steps performed by an analyst to accomplish a complete business transaction. It’s initiated by an actor, provides value to that actor, and is a goal of the actor working in that system.

• Use case diagrams provided a bird's-eye view of the basic functionality of the business processes contained in the evolving system.
• A use case diagram serves as a visual table of contents to use case descriptions.
• Activity diagrams provide a more-detailed graphical view of the underlying activities that support each business process.

Use case descriptions provide a means to more fully document the different aspects of each individual use case diagram.

• The use case descriptions are based on the identified requirements, use case diagram, and the activity diagram descriptions of the business processes.
• Use case descriptions contain all the information needed to document the functionality of the business processes.
• A use case description contains all the information needed to build the structural and behavioral diagrams that follow, but it expresses the information in a less-formal way that is usually simpler for users to understand.

Section 2: Example of Use Case Description

Section 3: Elements of a Use Case Description

• Overview:
  • Name, ID Number, Importance Level, Primary Actor, Type, Stakeholder(s), Brief Description, Trigger(s)
    • Title – descriptive name, matches name in use case diagram.
    • Primary actor – usually a user role.
    • Stakeholders – any group or individual with an interest in the function of the use case.
    • Trigger – an event or action that initiates the use case.
• Relationships:
  • Association: Communication between the use case and the actors
  • Include: Includes another use case
  • Extend: Extends the functionality of a use case
  • Generalization: Allows use cases to support inheritance
• Flow of events:
  • Normal flow: the usual set of activities
  • Sub-flows: decomposed normal flows to simplify the use case
  • Alternate or exceptional flows: those not considered the norm
• Optional characteristics:
  • complexity, time, etc.

Supplemental Notes

Section 4: Use Case Writing Guidelines

1. Write in the form of subject-verb-direct object.
2. Make sure it is clear who the initiator of the step is.
3. Write from independent observer’s perspective.
4. Write at about the same level of abstraction.
5. Ensure the use case has a sensible set of steps.
6. Apply the KISS principle liberally.
7. Write repeating instructions after the set of steps to be repeated.

Section 5: Creating Use Case Descriptions

1. Pick a high priority use case and create an overview:
   1. List the primary actor
   2. Determine its type (overview or detail; essential or real)
   3. List all stakeholders and their interests
   4. Determine the level of importance of the use case
   5. Briefly describe the use case
   6. List what triggers the use case
   7. List its relationship to other use cases
2. Fill in the steps of the normal flow of events required to complete the use case
3. Ensure that the steps listed are not too complicated or long and are consistent in size with other steps
4. Identify and write the alternate or exceptional flows
5. Carefully review the use case description and confirm that it is correct
6. Iterate over the entire set of steps again

Section 6: Resources

• How to Create Use Case Description
• Video: Use Case Descriptions
  
• Video: 5 Steps to Better Use Cases - Part 1
  
• Video: 5 Steps to Better Use Cases - Part 2