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Requirements Management with Use Cases

Requirements Management with Use Cases. Module 2 Introduction to RMUC. RMUC: Course Outline. 0 - About This Course 1 - Best Practices of Software Engineering 2 - Introduction to RMUC 3 - Analyzing the Problem 4 - Understanding Stakeholder Needs 5 - Defining the System

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Requirements Management with Use Cases

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  1. Requirements Management with Use Cases Module 2 Introduction to RMUC

  2. RMUC: Course Outline 0 - About This Course 1 - Best Practices of Software Engineering 2 - Introduction to RMUC 3 - Analyzing the Problem 4 - Understanding Stakeholder Needs 5 - Defining the System 6 - Managing the Scope of the System 7 - Refining the System Definition 8 - Managing Changing Requirements 9 - Requirements Across the Product Lifecycle

  3. Problem Space Problem Needs Solution Space Features Traceability The Product To Be Built Software Requirements Test Procedures Design User Docs Introduction to RMUC: Overview

  4. The GOAL is to deliver quality products on time and on budget which meet the customer’s real needs. Why Are We Here?

  5. Agreement on What the System Should Do The Goal Customer User Community System To Be Built RequirementsVerification Surrogate Goal Requirements Adapted from Al Davis

  6. Definitions: Requirements and Their Management • A requirement is a condition or capability to which the system must conform • Requirements management is a systematic approach to • Eliciting, organizing, and documenting the requirements of the system, and • Establishing and maintaining agreement between the customer/user and the project team on the changing requirements of the system

  7. Needs Vision Document Features Supplementary Specifications SoftwareRequirements Use-Case Model Requirements Specifications Test Specifications Design Specifications User Documentation Specifications

  8. Attributes Traceability Linking Requirements

  9. 1) User Involvement 15.9% 13.9% 2) Executive Management Support 3) Clear Statement of 11.8% Requirements What Factors Contribute to Project Success? Project Success Factors However... • Only 16% of projects completed on time and on budget (all companies) • 9% (large companies) • 28% (small companies) • 53% of projects over-ran their original estimates • Average overrun: 189% (+$59 billion) • 31% of projects canceled before completion ($81 billion) Why are these results so bad? Standish Group, ‘95 (www.standishgroup.com)

  10. Project Challenged (over-runs) Factors Project Impaired (canceled) Factors What Factors Contribute to Project Failure? Standish Group, ‘95 (www.standishgroup.com)

  11. How Can a Use-Case Model Help? • Models the system to be built • Ways to use the system (“use cases”) • Surroundings: who interacts with the system (“actors”) • Provides unifying thread for system development • Goal is for the system to meet customer requirements • The same use-case model is used in Requirements, Analysis & Design, and Test The most important role of a use-case model is to communicate the system’s functionality and behavior to the customer or end user.

  12. Actor Use Case Use-Case Model: Major Concepts • An actor represents an external entity that interacts with the system. • A use case defines a sequence of actions performed by a system that yields an observable result of value to an actor.

  13. What Is a Use-Case Model? A Sample System An Automated Teller Machine (ATM) Withdraw Cash Customer Bank Consortium Transfer Funds Deposit Funds Cashier MaintenanceCrew Maintain ATM A model of what the system is supposed to do (use cases), and the system's surroundings (actors).

  14. Use-Case-Model Survey - survey description - list of all actors - list of all use cases Bank Consortium Maintenance Crew Customer Cashier Withdraw Cash - brief description - flow of events Deposit Funds - brief description - flow of events Maintain ATM - brief description - flow of events A Use-Case Model Is Mostly Text! An ATM Withdraw Cash Transfer Funds Deposit Funds Transfer Funds - brief description - flow of events Maintain ATM

  15. Exercise: A Sample Use-Case Model 1. Read the Requested Features and User Interfacesketch for the Sample (ATM) System on the following two slides. 2. Now, look at Sample Use-Case Modelin the Handouts: • Use-Case-Model Survey for ATM in Handout UC 1 • Use-Case Reportfor Withdraw Cash in Handout UC 3.1 • Don’t worry about understanding everything in the reports. Just observe the structure and content. Handout UC1 and UC3.1

  16. Sample System: Requested Features • Design the software for an automated teller machine (ATM). The ATM requests necessary information from the bank by communicating with the bank’s computer system. • The ATM accepts a cash card, interacts with the user via a display and a key pad, communicates with the bank computer to carry out the transaction, receives and dispenses cash, and prints out a receipt. • A user should be able to withdraw cash, transfer funds between two of her accounts, and deposit to an account. • When a transaction is finished, the card is ejected. • The system requires appropriate record keeping and security provisions.

  17. 7 8 9 4 5 6 1 2 3 0 Ready Undo Help Card Reader Printer Deposit Input Cash Dispenser Sample System: Sketch of User Interface

  18. Benefits of a Use-Case Model • Use cases are concise, simple, and understandable by a wide range of stakeholders • Use terminology that customers and users understand • Verify developer understanding • Use cases give context for requirements • Identify the role of the users of the system • Identify system interfaces • Put system requirements in logical sequences • Help verify that all requirements are captured • Use cases facilitate agreement with the customer on system requirements

  19. A Use-Case Model Helps with ‘Scope Creep’ • The customer is aware there is a change to the use-case model • Makes the cost impact visible to the customer I’ll need a new use case and change some existing use cases... Customer

  20. The High Cost of Requirement Errors The 1-10-100 Rule “All together, the results show as much as a 200:1 cost ratio between finding errors in the requirements and maintenance stages of the software lifecycle.” Stage Requirements Time .1-.2 0.5 Design 1 Coding 2 Unit Test 5 Acceptance Test 20 Maintenance Relative Cost to Repair Errors: When introduced vs. when repaired Average cost ratio 14:1Grady 1989 Boehm 1988

  21. Involve the Whole Team in Requirements • Developers, Testers, Writers • Help develop requirements management practices • Monitor adherence to these practices • Verify elicitation process and outcomes • Help document and communicate requirements • Participate in requirements reviews and customer walkthroughs • Review traceability outcomes • Verify quality and completeness • Participate in or chair a CCB (Change Control Board)

  22. Review: Introduction to RMUC 1. What is our goal? 2. How can we “measure” quality? • What are the FURPS categories of requirements? • What categories within each of these apply to your product? 3. Why is it important to establish a baseline? How is it done? 4. How can a Use-Case Model help in developing our project? 5. What does the “1-10-100 Rule” tell us about finding defects? 6. What are some ways to involve the development team early?

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