Requirements Gathering Through Use Cases

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Requirements Gathering Through Use Cases
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A Short Course in Use Case Modeling

• Presented by David Naney

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Topics of Discussion

• Use Case Definition
• The Primary Uses of Use Cases
• Development of Use Cases
• Potential Problems with Use Cases
• Bibliography and Suggested Reading

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Use Case Definition

• A description of a complete course of events
  initiated by a user of the future system and of
  the interaction between the user and the system.
• (Object-Oriented Software
  engineering A Use Case Driven ApproachJacobson
  1992)
•  A use case is a typical interaction between a
  user and a computer system.
• A Use Case is a collection of scenarios.

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The Primary Uses

• Primary Uses What are Use Cases for?
• Use Cases are used primarily to capture the high
  level user-functional requirements of a system.
• In our research, we have used Use Cases to
  develop the core requirements of a system. They
  are useful in the development of Enduring
  Business Themes and Business Objects, terms that
  you should all be familiar with if you have read
  the assigned paper,
  Accomplishing Software Stability.
• Note Use Cases are for modeling what our system
  is going to do, not how it will do it.

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Any Other Uses?

• To act as a spring board for the software design
• Something to validate the software design against
• Software Testing and Quality Assurance

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How long do Use Cases go?

• Until all the interactions relate to the same
  goal.
• Interactions start at the triggering event and
  end when the goal is delivered or abandoned.
  (From Structuring Use
  Cases with Goals by Alistair Cockburn)

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Developing Use Cases

• Remember Use Cases are for modeling WHAT our
  system is going to do, not how it will do it.
• Other parts of the Unified Modeling Language
  (UML), of which Use Cases are but one part, are
  designed to model HOW the system is developed.

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The Use Case Template
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A System For Developing Use Cases

• Identify who is going to be using the system
  directly. These are the Actors.
• Pick One of the Actors.
• Figure out what the Actor wants to do with the
  system. These things, that the actor wants to do
  with the system, comprise a Use Case.
• Decide upon the usual course that this Use Case
  will take when that Actor is using the system.
  This is the basic course.
• Describe that basic course in the description
  for the Use Case.

from Use Case Modeling Capturing User
Requirements by Edward Kenworthy
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A System for Developing Use Cases

• Next, figure out if the Use Case has any
  alternative paths. If so, add those as extending
  Use Cases.
• Repeat each of these steps for each Actor.

from Use Case Modeling Capturing User
Requirements by Edward Kenworthy
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Modeling Problem

• You have been asked to develop the software for
  an online banking system. As an Object-Oriented
  Software Engineer, naturally, you want to start
  gathering the requirements from the users.
• Who are they?
• These are your Actors!

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Modeling Problem

• Now Pick one!
• What does this actor want to do with the system?
  These actions are the Use Case.
• Decide on a basic course.
• Does this Use Case have any alternative paths?
  Add these as extending Use Cases.

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Visualizing Your Use Cases

• Frequently, a Use Case Diagram is built, to show
  the interactions between the Actor and the
  system, and to show the different scenarios
  associated with the Use Case.

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Sample Use Case Diagram
from Use Case Modeling Capturing User
Requirements by Edward Kenworthy
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Possible Problems with Use Cases

• Over modeling Leads to requirement inflation.
• Use Cases emphasize ordering. This can be
  considered to be incompatible with object
  technology.

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Bibliography and Suggested Reading

• Object-Oriented Software Engineering A use
  Case Driven Approach, by Ivar Jacobsen
• Use Case Modeling Capturing User Requirements
  by Edward Kenworthy (http//www.zoo.co.uk/z00010
  39/PracGuides/pg_use_cases.htm)
• Structuring Use Cases With Goals by Alistair
  Cockburn
• (http//members.aol.com/acockburn/papers/use
  cases.htm)
• Use Cases Fundamentals by Alistair Cockburn
• (http//members.aol.com/acockburn/papers/Al
  tIntro.htm)
• OOSC2 The Use Case Principle by Bertrand Meyer
  (http//www.elj.com/elj/v1/n2/bm/use-cases/)
• The Roles of Use Cases in Analysis by Daniel A.
  Rawsthorne, PhD (http//www.pols.co
  .uk/usecasezone/UseCaseConcepts.html)
• The Misuse of Use Cases By Dr. Timothy Korson
  (http//www.software-architects.com/publica
  tions/korson/Korson9803om.htm)
• Constructing Useful Use Cases By Dr. Timothy
  Korson (http//www.software-architects.com/publica
  tions/korson/usecase3/)