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Sponsored by:
The Use Case Technique:
An Overview
Karl Wiegers
Principal Consultant, Process Impact
www.processimpact.com
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Sponsor: RequirementOne
� Save time. Capture use cases quickly in intuitive Word format and accurately with all attributes in one central location
� Quick to implement. Less than 2 minutes to create account + add first requirement
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Phone #:
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Sponsored By
Blog:
Featured Speaker
Karl Wiegers
Principal Consultant, Process Impact
www.processimpact.com
503-698-9620
Consulting Tips & Tricks Blog: www.karlconsulting.blogspot.com
Downloadable Process Goodies: www.processimpact.com/goodies.shtml
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Source Books
�More about Software Requirements, by Karl E. Wiegers (Microsoft Press, 2006)
�Use Cases: Requirements in Context, 2nd Ed., by Daryl Kulak and Eamonn Guiney (Addison-Wesley, 2003)
� Software Requirements,2nd Ed., by Karl E. Wiegers(Microsoft Press, 2003)
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Agenda
�Use cases defined
�Benefits of the use case approach
�User classes and actors
� Scenarios and use cases
�Use case elicitation workshops
�Elements of a use case
�Use cases and functional requirements
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Three Levels of Software Requirements
BusinessRequirements
Vision and Scope Document
UserRequirements
Use Case Document
FunctionalRequirements
Software Requirements Specification
Constraints
External Interfaces
BusinessRules
QualityAttributes
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Eliciting Requirements Through Use Cases
� Use cases came from object-oriented world, apply to general
requirements analysis.
� Provides a method to capture user requirements.
� Focus on actual, but abstracted, usage scenarios.
� Ask users:
“Describe a goal you wish to accomplish with the system.”
not:
“What do you want the system to do?”
� Explore sequences of ‘actor’ actions and system responses.
� Derive functional requirements and tests from use cases.
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What Use Cases Are and Are Not
� Definition:A description of a set of interaction sequences that a system performs to provide a result of observable or measurable value to one or more actors.
� Use cases describe:� user goals
� the user’s view of the system
� a set of task-related activities
� Use cases do not describe:� user interface designs
� technology solutions
� application architecture
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Benefits from the Use Case Approach
� User-centric: user’s terminology is applied
� Task-centric: reveals requirements to get
work done
� Helps analysts understand application domain
� Helps avoid building unnecessary functionality
� Permits early drafting of functional tests
� Helps set implementation priorities on functional
requirements
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Appropriate Use Case Applications
� Use cases work well for:
� end-user applications
� web sites
� devices with which users must interact
�Use cases aren’t as valuable for:
� batch processes
� computationally-intensive systems
� event-driven real-time systems
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Examples of Use Cases
� Intuit QuickBooks “activities”:
� Write a Check � Create an Invoice
� Enter Credit Card Charge � Receive Payment
�Amazon.com options for an accepted order:
� Check Order Status � Change Shipping Options
� Cancel Unshipped Items � Track Package
�Buy a product online:
� Search Catalog
� Place Item in Shopping Cart
� Pay for Items in Shopping Cart
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Naming Use Cases
�Name properties:� reflect the actor’s goal from the actor’s perspective
� describe a valuable transaction
� be general enough to cover related scenarios
� Form: active verb + object� “Generate Usage Report,” not “Usage Report Generation”
� use strong verbs and specific nouns
Good Examples:
� Reserve Rental Car� Print Invoice
� Check Flight Status
Not So Good Examples:
� Enter PIN� Submit Form 37� Process Deposit
Hi! My name is:
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User Classes and Actors
�User Classes: Distinct communities of users for the product.
�Actors: Entities outside the system that interact with it for
the purpose of completing an event.
User Classes Actors
Bank CustomerAccount OwnerLoan Applicant
Depositor
ChemistTechnician
Stockroom StaffLab Manager
ChemicalRequester
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Scenarios and Use Cases - 1
� A scenario is:
� one specific path through a use case, or
� a story about a specific instance of a use case execution,
perhaps with actual users identified and specific data
� Each use case typically includes multiple scenarios.
� could be successful or could be failure modes
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Scenarios and Use Cases - 2
MoreAbstract
LessAbstract
Prepare a mailing label
Chris wants to send a 2.5-pound package by second-day UPS from Portland, OR, to Rochester, NY. She wants it insured for $75 and she wants a return receipt. The package is marked fragile.
Prepare a mailing label to send a package by second-day UPS.
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Use Case Elicitation Workshop
Use Case:
Actor: Requester Frequency: 5/user/day
View an order.
Preconditions: system contains orders;
user’s identity is verified
Actor Actions System Responses
user enters order
number he wants
to view
user enters order
number, but it
doesn’t exist
error message:
order number
not found
display order
details
Postconditions: order has been shown
etc. for all normal
and exception
pathways
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Products from Use Case Analysis
Use Case
Workshops
Use Case
Descriptions
Draft SRS
Business
Rules
Verified
Models
Data
Dictionary
Draft Models
Draft Tests
Verified
SRS
Shared
Vision
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Use Case Template
Actors:
Description:
Trigger:
Preconditions:
Postconditions:
Normal Flow:
Alternative Flows:
Exceptions:
Includes:
Priority:
Frequency of Use:
Business Rules:
Special Requirements:
Assumptions:
Notes and Issues:
Use Case ID:
Use Case Name:
Created By: Last Updated By:
Date Created: Date Last Updated:
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Sample Use Case for an ATM - 1Name: Withdraw Cash
Actor: Account Owner
Description:
The user withdraws a specific amount of cash from a specified account.
Trigger: Account Owner selects Withdrawal action.
Preconditions:
1. The Account Owner is logged in to the ATM.2. The Account Owner has at least one account with a positive balance.3. The ATM contains cash.
Postconditions:
1. The requested amount of cash has been dispensed.2. The account balance is reduced by the amount withdrawn plus any fees.3. The ATM cash balance is reduced by the amount withdrawn.
Priority: High
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Sample Use Case for an ATM - 2
Normal Flow:
1. System displays user’s accounts.
2. Account Owner selects desired account.
3. System asks user to choose amount to withdraw from a list.
4. Account Owner chooses amount to withdraw.
5. System dispenses cash.
6. Account Owner removes cash from dispenser.
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Sample Use Case for an ATM - 3
Alternative Flows:
� at step 3, actor can choose to enter a custom amount
� describe where the branch takes place, what happens,
and where the alternative flow rejoins the main flow
Exceptions:
� amount is not a multiple of $20
� amount exceeds daily withdrawal limit
� amount exceeds account balance
� amount exceeds cash available in ATM
� indicate the step number where the exception could take place and how the system handles it
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Use Cases and Functional Requirements - 1
Use Cases
User View
FunctionalRequirements
Developer View
� Two schools of thought:
� Use cases are the functional requirements.
� Use cases reveal the functional requirements.
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Use Cases and Functional Requirements - 2
�Precondition
� “The system shall verify that the account is set up for ATM withdrawals.”
� Steps in Flow
� “The system shall display a list of standard withdrawal amounts. The user shall select one of these amounts or ‘Other’.”
�Postcondition
� “The system shall reduce the total cash remaining in the ATM by the amount of the withdrawal.”
�Business Rule
� “The system shall print the available balance on the receipt, unless the account is a business account.”
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Organizing Information: Use Case and SRSUse Case Organization SRS Organization
Pre
Rules
Post
Other
E
A
Normal
Flow
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~
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The Use Case Technique: An Overview
NONONONONONONONO
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Q & A