Hi600 ch04_text_slides

Use Case Analysis
SYSTEMS ANALYSIS AND DESIGN, 6TH EDITION
DENNIS, WIXOM, AND ROTH
© COPYRIGHT 2015 JOHN WILEY & SONS, INC. 1

Learning Objectives
 Explain the purpose of use cases in the analysis phase of the
SDLC.
 Describe the various parts of a use case and the purpose of each
part.
 Describe how use cases contribute to the functional requirements.
 Describe how use cases inform the development of test plans.
 Explain the process used to create a use case.

What is a Use Case?
UNDERSTANDING THE PURPOSE OF THIS TOOL

Role of Use Cases
 Use cases express and clarify user requirements.
 Purpose - define the expected interaction between user and
system.
 Use that interaction to more fully describe functional requirements
 Used extensively in the analysis phase. Often a part of user
interviews or JAD sessions.
 Text-based use cases are easy for the users to understand.
 Flow easily into the creation of process models and the data
model.

Use Cases
 Represents how a system interacts with its environment
 Illustrates the activities that are performed by the users and
the system’s responses.
 Activities produce some output result.
 Each use case describes how an external user triggers an
event to which the system must respond.
 In event-driven modeling, everything in the system can be
thought of as a response to some triggering event.

Use Case Styles
ELEMENTS AND FORMATS

Elements of a Use Case
 Each use case has a name and number, and brief description.
 The priority may be assigned to indicate the relative
significance.
 The actor refers to a person, another system, or a hardware
device that interacts with the system to achieve a useful goal.
 The trigger for the use case – the event that causes the use
case to begin.
 Events triggers can be external or temporal

Use Case Basic
Information
From Figure 4-1
Casual Format Use Case

Normal Course
o The major steps that are performed
to execute the response to the event

Exceptions
o Error conditions encountered while
performing use case steps.
o NOT normal branches in decision
logic.
o Lead to an unsuccessful result.

Use Cases in
Sequence
o Uses cases often performed in
sequence.
o No single use case should be too
large.
o Important to define initial and
ending states.

Preconditions
and
Postconditions
o Preconditions define what must be
complete before beginning this use
case.
o Postconditions define what is
complete when this use case ends.

Fully-Dressed Use Case Format
 Very thorough, detailed, and highly structured.
 Adds new sections, including,
o Alternative courses
o Inputs and outputs for steps
o Summary inputs and outputs.
See Figure 4-3 for example

Fully-Dressed Use Case Format, con’t.
Use this format when:
o Users are not closely engaged with development team
o Project has high complexity and high risk
o Test cases need to be fully described
o Remote collaborating teams need detailed, shared
understanding of user needs.

Use Case Practical Tips
 Use gradual refinement.
 Concentrate on describing the user’s objectives with the
system completely and accurately.
 Keep both audiences in mind – users and developers.
 Create use cases only when needed to clarify what the
system must do from the user’s perspective. Not
needed for simple events.

Use Cases and the Functional
Requirements
 Use cases are useful tools to clarify user requirements.
 Use cases convey only the user’s point of view.
 Transforming the user’s view into the developer’s view
through functional requirements is one of the system
analyst’s key contributions.
 The derived functional requirements tell the developers
more about what the system must do.
© COPYRIGHT 2011 JOHN WILEY & SONS, INC. 4-16

Detailed
Functional
Requirements
Use case content used to create more
complete and descriptive functional
requirements

Creating Use Cases
 Identify events the system must respond to – develop
Event-Response List
 Create use case form for the complex events
 For each use case:
o Identify the major steps
o Identify elements with each major step (inputs and outputs)
o Confirm use case with users through role-playing
 Revise functional requirements as needed

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