The Use Case Technique: An Overview Karl Wiegers Process Impact www.processimpact.com Copyright 2018 Karl Wiegers version 3 Source Books Software Requirements,3rd Ed., by Karl Wiegers and Joy Beatty (Microsoft Press, 2013) 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) The Use Case Technique: An Overview 2 Copyright © 2018 Karl Wiegers The Use Case Technique: An Overview Copyright 2018 Karl Wiegers Page 1 Agenda Use cases defined Use cases and user stories Benefits of the use case approach User classes and actors Use case elicitation workshops Elements of a use case Use cases and functional requirements Use case traps to avoid The Use Case Technique: An Overview 3 Copyright © 2018 Karl Wiegers Three Levels of Software Requirements Business Requirements Business Rules Vision and Scope Document User Quality Requirements Attributes User Requirements Document External Interfaces Functional Requirements Constraints Software Requirements Specification The Use Case Technique: An Overview 4 Copyright © 2018 Karl Wiegers The Use Case Technique: An Overview Copyright 2018 Karl Wiegers Page 2 Eliciting Requirements Through Use Cases 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. The Use Case Technique: An Overview 5 Copyright © 2018 Karl Wiegers 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 The Use Case Technique: An Overview 6 Copyright © 2018 Karl Wiegers The Use Case Technique: An Overview Copyright 2018 Karl Wiegers Page 3 Examples of Use Cases Intuit QuickBooks “activities”: Enter Credit Card Charge Enter a Bill Create an Invoice Reconcile Account Pay Bills Receive Payment Amazon.com options for a pending 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 The Use Case Technique: An Overview 7 Copyright © 2018 Karl Wiegers 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: Poor Examples: Reserve Rental Car Enter PIN Print Invoice Submit Form 37 Register for Payroll Deduction Process Deposit Check Flight Status Manage Menus The Use Case Technique: An Overview 8 Copyright © 2018 Karl Wiegers The Use Case Technique: An Overview Copyright 2018 Karl Wiegers Page 4 Agile User Stories A “short, simple description of a feature told from the perspective of the person who desires the new capability, usually a user or customer of the system” (Mike Cohn). serve as placeholder for future conversations for details augmented with acceptance tests don’t get into user interaction specifics A common writing style: As a <type of user>, I want <some goal> so that <some reason>. The Use Case Technique: An Overview 9 Copyright © 2018 Karl Wiegers Use Cases and User Stories “Create an Invoice” functional Use requirements Case conversations use case analysis specification Name tests “As a small business owner, I want to create an invoice so that I can bill a customer.” User conversations refined user conversations acceptance Story stories tests The Use Case Technique: An Overview 10 Copyright © 2018 Karl Wiegers The Use Case Technique: An Overview Copyright 2018 Karl Wiegers Page 5 Benefits from the Usage-Centric Approach User’s terminology is applied Reveals requirements for users to get work done Helps analysts understand application domain Avoids building unnecessary functionality Permits early drafting of functional tests Helps set implementation priorities on functional requirements The Use Case Technique: An Overview 11 Copyright © 2018 Karl Wiegers Appropriate Use Case Applications Use cases work well for: end-user applications business automation projects web sites devices with which users must interact Use cases aren’t as valuable for: batch processes event-driven real-time systems computationally-intensive systems business analytics systems The Use Case Technique: An Overview 12 Copyright © 2018 Karl Wiegers The Use Case Technique: An Overview Copyright 2018 Karl Wiegers Page 6 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 The Use Case Technique: An Overview 13 Copyright © 2018 Karl Wiegers 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 The Use Case Technique: An Overview 14 Copyright © 2018 Karl Wiegers The Use Case Technique: An Overview Copyright 2018 Karl Wiegers Page 7 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 Abstract Rochester, NY. She wants it insured for $75 and she wants a return receipt. The package is marked fragile. The Use Case Technique: An Overview 15 Copyright © 2018 Karl Wiegers Use Case Elicitation Workshop Use Case: View an order. Actor: Requester Frequency: 5/user/day Preconditions: system contains orders, user 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 The Use Case Technique: An Overview 16 Copyright © 2018 Karl Wiegers The Use Case Technique: An Overview Copyright 2018 Karl Wiegers Page 8 Products from Use Case Analysis Drafted SRS Verified SRS Drafted Tests Verified Shared Models Vision Use Case Use Case Drafted Models Workshops Descriptions Business Rules Data Dictionary The Use Case Technique: An Overview 17 Copyright © 2018 Karl Wiegers Use Case Template ID and Name: Created By: Date Created: Primary Actor: Secondary Actors: Description: Trigger: Preconditions: Postconditions: Normal Flow: Alternative Flows: Exceptions: Priority: Frequency of Use: Business Rules: Other Information: Assumptions: The Use Case Technique: An Overview 18 Copyright © 2018 Karl Wiegers The Use Case Technique: An Overview Copyright 2018 Karl Wiegers Page 9 Sample Use Case for an ATM - 1 Name: Withdraw Cash Actor: Account Owner Description: The user withdraws a specific amount of cash from an 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 1 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 The Use Case Technique: An Overview 19 Copyright © 2018 Karl Wiegers 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. The Use Case Technique: An Overview 20 Copyright © 2018 Karl Wiegers The Use Case Technique: An Overview Copyright 2018 Karl Wiegers Page 10 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 The Use Case Technique: An Overview 21 Copyright © 2018 Karl Wiegers 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 Functional Use Cases Requirements The Use Case Technique: An Overview 22 Copyright © 2018 Karl Wiegers The Use Case Technique: An Overview Copyright 2018 Karl Wiegers Page 11 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