UseCase Modeling

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Use-Case Modeling

• Based on pp. 239-246 of Hoffer, George, and
  Valicich and Chapter 6 of Systems Analysis
  Design An Object-Oriented Approach with UML by
  Alan Dennis, Barbara Wixom, and David Tegarden
  published by John Wiley Sons, Inc., 2002
  (http//www.wiley.com/college/dennis)

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Agenda

• What is a use case (with examples)
• Guidelines for developing use-case descriptions
• Guidelines for drawing use-case diagrams
• Exercise

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Learning Objectives

• After this lecture, you should be able to
• Describe what a use case is
• Describe the deliverables from use-case modeling
• Develop a simple use-case description and
  use-case diagram

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Example Use-Case Diagram
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Example Use-Case Description
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Use-Case Modeling

• A foundation of the object-oriented approach to
  systems analysis and design
• An approach to understanding functional
  requirements of a system within the Analysis
  Phase of the SDLC
• High level description of what the system needs
  to do
• Each use case describes one function involving
  one or more users interacting with the system

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So What is a Use Case?

• From a users perspective A use case is a
  discrete activity or function that a user
  performs via the system
• From the systems perspective A use case is a
  discrete activity or function that the system
  performs for a user

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Deliverables for Use-Case Modeling

• Types of deliverables
• Text-based descriptions of each use case
• Formal use-case diagrams
• Focus of deliverables
• Current (as-is) system
• New (to-be) system
• Level of abstraction in deliverables
• Logical / essential (what system should do
  without specifying how)
• Physical / real (how functionality is
  implemented)
• Level of detail in deliverables
• Overview
• Detail

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Use-Case Descriptions

• Capture typical interactions of the system with
  the systems users
• Each use case is a single function or user role
• Elements
• Overview Information
• E.g., name (verb-noun phrase, such as Place
  order)
• E.g., sentence describing the essence of the use
  case
• Relationships (with other use cases and users)
• Flow of Events
• Optional Characteristics
• Developed iteratively

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Guidelines for Developing Use-Case Descriptions

• Identify the Major Use Cases
• Find the systems boundaries
• List the primary actors
• List the goals of the primary actors
• Identify and write the overview of the major use
  cases for the above
• Carefully review the current use cases. Revise
  as needed.

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Guidelines for Developing Use-Case Descriptions

• Expand the Major Use Case
• Choose one of the use cases to expand
• Start filling in the details of the chosen use
  case
• Write the normal flow of events for the use case
• If the normal flow of events is too complex or
  long, decompose into subflows
• List the possible alternate or exceptional flows
• For each alternate or exceptional flow, list how
  the actor and/or the system should react

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Guidelines for Developing Use-Case Descriptions

• Confirm the Major Use Cases
• Carefully review the current set of use cases.
  Revise as needed.
• Start at the top again.

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Guidelines for Developing Use-Case Diagrams

• Draw the system boundary
• Place the use cases on the diagram
• Place the actors on the diagram
• Draw the associations

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Exercise
Identify Use Cases and Develop a Use-Case Diagram
and a Use-Case Description for the Open Road
Insurance system Open Road Insurance (ORI) is an
independent agency that receives policy contracts
from various insurance companies. The purpose of
the ORI system is to provide automotive insurance
to car owners. Initially, a customer applies for
coverage via an application. The agency requests
a drivers record report from the local police
department. The agency also requests vehicle
registration confirmation from the Department of
Motor Vehicles. An agent determines the best
policy for the type and level of coverage desired
and sends the customer a copy of the insurance
policy along with an insurance coverage card.
The customer information is stored.
Periodically, the system generates a fee
statement, which along with addendums to the
policy is sent to the customer, who responds by
sending in a payment with the fee stub.
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Exercise

• One Solution
• Use-Case Diagram
• Use-Case Description for Apply for Coverage

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Summary

• What is a use case?
• What are the deliverables from use-case modeling?
• How do use-case models fit into the SDLC?

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Guidelines for Developing Use-Case Descriptions

• Write the normal flow of events (i.e., the
  essence of the use case)
• Write each step in the form of Subject-Verb-Direct
  Object (and sometimes Preposition-Indirect
  Object)
• Make sure it is clear who the initiator of the
  step is
• Write the steps from the perspective of an
  independent observer
• Write each step at about the same level of
  abstraction
• Ensure the use case has a sensible set of steps
• Apply the KISS principle liberally
• Write repeating instructions after the set of
  steps to be repeated