The Use Case Technique: An Overview

Transcription

1 The Use Case Technique: An Overview Sponsored by: Karl Wiegers Principal Consultant, Process Impact

2 Sponsor: CEG Save 20% on training* with promo code: MAWEB14 Free BA online training demo: View course schedule at Tailored Corporate Training Open-Enrollment Courses Multiple Delivery Methods Learn from Certified Industry Practitioners BA, PM, PRINCE2, BPM, M&L Earn a Business Analysis Certificate through our Duke University Alliance Endorsed Education Provider for IIBA 2

3 Featured Speaker Karl Wiegers Principal Consultant, Process Impact Phone #: Blog: Consulting Tips & Tricks Blog: Downloadable Process Goodies: 3

4 Source Books Software Requirements, 3 rd Edition, by Karl Wiegers and Joy Beatty (Microsoft Press, 2013) amzn.to/1auzx1m More About Software Requirements, by Karl E. Wiegers (Microsoft Press, 2006) Use Cases: Requirements in Context, 2 nd Edition, by Daryl Kulak and Eamonn Guiney (Addison-Wesley, 2003) 4

5 Agenda Use cases defined Use cases and user stories Benefits of the usage-centric approach User classes and actors Use case elicitation workshops Elements of a use case Use cases and functional requirements 5

6 Three Levels of Software Requirements Business Requirements Business Rules Vision and Scope Document User Requirements Quality Attributes User Requirements Document Functional Requirements External Interfaces Constraints Software Requirements Specification 6

7 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. Sponsored By 7

8 What Use Cases Are and Are Not Definition: A use case describes a sequence of interactions between a system and an external actor that results in the actor being able to achieve some outcome of value. 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 8

9 Examples of Use Cases Intuit QuickBooks activities : Write a Check Enter Credit Card Charge Create an Invoice 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 9

10 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 Hi! My name is: 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 10

11 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>. 11 Sponsored By

12 Create an Invoice Use Cases and User Stories Use Case Name conversations use case specification analysis functional requirements tests As a small business owner, I want to create an invoice so that I can bill a customer. User Story conversations refined user stories conversations acceptance tests 12

13 Benefits from Usage-Centric Approach User s terminology is applied Reveals requirements for users to get tasks done Helps analysts understand application domain Helps avoid building unnecessary functionality Permits early drafting of functional tests Helps set implementation priorities on functional requirements 13

14 Appropriate Use Case Applications Use cases work well for: end-user applications business automation projects websites 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 14 Sponsored By

15 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 Bank Customer Chemist Technician Stockroom Staff Lab Manager Actors Account Owner Loan Applicant Depositor Chemical Requester 15 Sponsored By

16 A scenario is: Scenarios and Use Cases 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 16 Sponsored By

17 Use Case Elicitation Workshop Use Case: View an order. Actor: Requester Preconditions: Postconditions: Frequency: 5/user/day system contains orders; user s identity is verified order has been shown Actor Actions user enters order number he wants to view System Responses display order details user enters order number, but it doesn t exist error message: order number not found etc. for all normal and exception pathways 17

18 Products from Use Case Analysis Drafted SRS Verified SRS Drafted Tests Use Case Workshops Use Case Descriptions Drafted Models Verified Models Shared Vision Business Rules Data Dictionary 18

19 Use Case Template ID and Name: Created By: Primary Actor: Description: Trigger: Preconditions: Postconditions: Normal Flow: Alternative Flows: Exceptions: Priority: Frequency of Use: Business Rules: Other Information: Assumptions: Date Created: Secondary Actors: 19 Sponsored By

20 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 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 20

21 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. 21

22 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 22 Sponsored By

23 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 Sponsored By Functional Requirements 23

24 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. Sponsored By 24

25 Organizing Information: Use Case and SRS Use Case Organization Pre Normal Flow Post Rules Other A E SRS Organization ~~~~~~~~~~~~ ~~~~~~~~~ ~~~~~~~~~ ~~~~~~~~~~~~ ~~~~~~~~~~~~ ~~~~~~~~~ ~~~~~~~~~ ~~~~~~~~~ ~~~~~~~~~ ~~~~~~~~~ ~~~~~~~~~ ~~~~~~~~~~~~ ~~~~~~~~~~~~ ~~~~~~~~~~~~ ~~~~~~~~~~~~ 25

26 The Use Case Technique: An Overview NO SURPRISES! 26

27 Sponsor: CEG Save 20% on training* with promo code: MAWEB14 Class Schedules Free Weekly Webinars Resource Center Contact: Earn a Certificate in Business Analysis Online Flexible Available On Demand, 24/7 Free Test Drive of the First Course! Great for Enterprise-Wide Deployment Also available in traditional classroom and virtual programs *Applies to open-enrollment courses only. Excludes Business Process Management courses. Special offers may not be combined with any other offers and may not be applied to new registrations preceded by a cancellation for the same class within the previous 30 days. Additional restrictions may apply. Offer expires 3/31/14. 27

28 Q & A 28