Tell a Story

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Tell a Story
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Use Case
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Function and Form
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First Form A NarrativeMake a Payment
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Narrative Form
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Second Form A ScenarioRegister Customer With
Automatic Activation
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Scenario Form
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Third Form A ConversationMake A Payment -
General Flow
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Conversation Form
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Comparing the Three Forms
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The Benefits of Use Cases
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Use Cases Aid Understanding
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Use Cases Vary by AbstractionLevel
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Use Cases Vary in Scope
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Use Cases Vary in Detail
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What Use Cases Cannot Do
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Finding Use Cases
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Finding Use Cases
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Naming Use Cases
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Primary and Secondary Actors
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Naming Actors

• Group individuals according to their common use
  of the system. Identify the roles they take on
  when they use or are used by the system
• Each role is a potential actor
• Name each role and define its distinguishing
  characteristics. Add these definitions to your
  glossary
• Dont waste time debating actor names

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Actor and Use Case Checklist
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Glossary
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Glossaries
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Build Consensus
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Defining Concepts

• Identify a concept and its distinguishing
  characteristics
• More than a synonym for a word
• Identifies a way of mentally dividing reality for
  purpose of talking or thinking

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Writing Glossary Entries

• Why this concept is important
• Typical sizes or values
• Clarify likely misunderstandings
• Show an example
• Explain graphical symbols
• Relate entries

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A Good Form for Definitions
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Improving Glossary Definitions
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Relating Definitions
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Define Acronyms and Their Concepts
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Avoid UsingIs When or Is Where
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Explain What Is Unclear
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Setting the Stage for the Use Case

• Levelsummary, core, supporting, or internal use
  case?
• Actor(s)role names of people, objects or
  external systems initiating this use case
• Contextthe current state of the system and actor
• Preconditionswhat must be true before a use case
  can begin

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Completing The Picture

• Variations different ways to accomplish use case
  steps
• Exceptions errors that occur during the
  execution of a step
• Policies specific rules that must be enforced by
  the use case
• Issues questions about the use case
• Design notes hints to implementers
• Post-conditions what must be true about the
  system after a use case completes
• Other requirements what constraints must this
  use case conform to
• Priority how important is this use case?
• Frequency how often is this performed?

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Make Clear What You Dont Know
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Avoid Vague Words
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Write General and Specific Cases
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Actor Actions
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Include System Actions
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Describing Actions
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Condense Information Entryand/or Validation
Actions
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State System Actions at aReasonably High Level
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Showing Optional and Repeated Actions