The Use Case Technique: An Overview
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Karl Wiegers Principal Consultant, Process Impact www.processimpact.com Sponsor: RequirementOne
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Karl Wiegers Principal Consultant, Process Impact www.processimpact.com
Phone #: 503-698-9620 E-mail: [email protected] Blog: Consulting Tips & Tricks Blog: www.karlconsulting.blogspot.com Downloadable Process Goodies: www.processimpact.com/goodies.shtml 3
Sponsored By Source Books
Software Requirements,2 nd Ed., by Karl E. Wiegers (Microsoft Press, 2003)
More about Software Requirements , by Karl E. Wiegers (Microsoft Press, 2006)
Use Cases: Requirements in Context, 2 nd Ed., by Daryl Kulak and Eamonn Guiney (Addison-Wesley, 2003)
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Sponsored By 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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Sponsored By Three Levels of Software Requirements
Business Requirements
Vision and Scope Document Business Rules User Requirements Quality Attributes Use Case Document External Interfaces Functional Requirements Constraints
Software Requirements Specification 6
Sponsored By 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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Sponsored By 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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Sponsored By 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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Sponsored By 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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Sponsored By 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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Sponsored By Naming Use Cases
Name properties: reflect the actor’s goal from the actor’s perspective describe a valuable transaction Hi! My name is: 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: Not So Good Examples: Reserve Rental Car Enter PIN Print Invoice Submit Form 37 Check Flight Status Process Deposit
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Sponsored By 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
Account Owner Bank Customer Loan Applicant Depositor Chemist Technician Chemical Stockroom Staff Requester Lab Manager
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Sponsored By 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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Sponsored By Scenarios and Use Cases - 2
More Abstract Prepare a mailing label
Prepare a mailing label to send a package by second- day UPS.
Chris wants to send a 2.5-pound package by Less second-day UPS from Portland, OR, to Rochester, Abstract NY. She wants it insured for $75 and she wants a return receipt. The package is marked fragile. 15
Sponsored By Use Case Elicitation Workshop
Use Case: View an order. Actor: Requester Frequency: 5/user/day Preconditions: system contains orders; user’s identity is verified Postconditions: order has been shown
Actor Actions System Responses
user enters order display order number he wants details to view
user enters order error message: number, but it order number doesn’t exist not found
etc. for all normal and exception pathways
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Sponsored By Products from Use Case Analysis
Draft SRS Verified SRS Draft Tests
Verified Shared Models Vision Use Case Use Case Draft Models Workshops Descriptions
Business Rules
Data Dictionary 17
Sponsored By Use Case Template
Use Case ID: Use Case Name: Created By: Last Updated By: Date Created: Date Last Updated: Actors: Description: Trigger: Preconditions: Postconditions: Normal Flow: Alternative Flows: Exceptions: Includes: Priority: Frequency of Use: Business Rules: Special Requirements: Assumptions: Notes and Issues: 18
Sponsored By Sample Use Case for an ATM - 1 Name: 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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Sponsored By 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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Sponsored By 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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Sponsored By Use Cases and Functional Requirements - 1
Two schools of thought: Use cases are the functional requirements. Use cases reveal the functional requirements. User View Developer View
Use Cases Functional Requirements
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Sponsored By 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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Sponsored By Organizing Information: Use Case and SRS Use Case Organization SRS Organization Pre ~~~~~~~~~~~~ ~~~~~~~~~ ~~~~~~~~~ Normal ~~~~~~~~~~~~ Flow ~~~~~~~~~~~~ ~~~~~~~~~ A ~~~~~~~~~ ~~~~~~~~~ ~~~~~~~~~ ~~~~~~~~~ E ~~~~~~~~~ Post ~~~~~~~~~~~~ ~~~~~~~~~~~~ Rules ~~~~~~~~~~~~ ~~~~~~~~~~~~ Other 24
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