3081 :
CSci L4.1: Software Specification and Design
Use Cases
Prof. Eric Van Wyk
Spring 2008
c Eric Van Wyk
CSci 3081: Program Design and Development -- Spring 2008
Page 1 / 9
Software Specification and Design
Use Cases:
Use Cases
A scenario is a "sequence of steps describing an interaction between a user and a system" A bit like part of a "trace" of a program. A use case is a collection of related scenarios. Specifies a few related traces. Describes alternative, possible failures and reactions. Read Fowler Chapter 9.
c Eric Van Wyk
CSci 3081: Program Design and Development -- Spring 2008
Page 2 / 9
Software Specification and Design
Use Cases:
Sample scenario
From Fowler, page 99. "The customer browses the catalog and adds desired items to the shopping basket. When the customer wishes to pay, the customer describes the shipping and credit card information and confirms the sale. The system checks the authorization on the credit card and confirms the sale both immediately and with a follow-up email." A scenario is "one thing that can happen."
c Eric Van Wyk
CSci 3081: Program Design and Development -- Spring 2008
Page 3 / 9
Software Specification and Design
Use Cases:
But what if the credit card authorization fails? What is the customer has shipping information in the system? What if we want to violate Amazon's "One-click" software patent. These are all related and the use cases for them may form a use case.
c Eric Van Wyk
CSci 3081: Program Design and Development -- Spring 2008
Page 4 9
Software / Specification and Design
Use Cases:
Actors, roles
We refer to users and entities in general as actors. More specifically, they are roles that actors may play.
c Eric Van Wyk
CSci 3081: Program Design and Development -- Spring 2008
Page 5 / 9
Software Specification and Design
Use Cases:
Use case standard formats
OK, there are no standard formats. But, a common approach identifies a "main success scenario" and describes what to do for failures as "extensions". Each has a primary actor. Each step is a element in the interaction.
c Eric Van Wyk
CSci 3081: Program Design and Development -- Spring 2008
Page 6 / 9
Software Specification and Design
Use Cases:
Exercise
You will turn this in before leaving. Form groups of two or more. Spend 5 minutes defining a use case for the project. We will read some and show them on the projector.
c Eric Van Wyk
CSci 3081: Program Design and Development -...