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REQUIREMENTS - WHY WHAT AND HOW?

This text provides an overview of the importance of software requirements management, including the impact of requirements on project success and failure, the definition and management of software requirements, and different software development lifecycle models.

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REQUIREMENTS - WHY WHAT AND HOW?

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  1. REQUIREMENTS - WHY WHAT AND HOW? Steve Chenoweth & Chandan Rupakheti CSSE 371 Chapters 1 - 4 Requirements Text . Question 6

  2. WHY REQUIREMENTS “Why not just ask them what they want, they tell you, and you build it?”

  3. Some facts • 250 billion dollar industry • 31% projects cancelled(money lost 81 billion dollars) • 52.7% cost 189% of their original estimates

  4. Biggest Reasons forProject Success and Failure

  5. Project Failure • Lack of user input (13%) • Incomplete requirements (12%) • Changing requirements (12%) Question 1

  6. Project Success • User involvement (16%) • Executive management support (14%) • Clear statement of requirements (12%)

  7. Defects by Development Phase • Requirements – 31% • Design – 25% • Coding – 12% • Documentation – 16% • Bad fixes – 16%

  8. Cost to Fix Errors 1 5 25 50 125 500 Requirements Design Coding Unit Test Acceptance Test Maintenance

  9. Why ? • Requirements errors are likely to be the mostcommon class of error • Requirements errors are likely to be the mostexpensive to fix

  10. WHAT IS A SOFTWARE REQUIREMENT? “I’d like to see the web pages in green…”

  11. What is a Software Requirement? • A software capability needed by the user to solve a problem to achieve an objective • A software capability that must be met or possessed by a system or system component to satisfy a contract, standard, specification or other formally imposed documentation Question 2

  12. What is Software Requirements Management? • The process of systematically, eliciting, organizing and documenting requirements for the software system, and a process that establishes and maintains agreement between the customer and the project team on the changing requirements of the system. Question 3

  13. What does it involve? • Understand the need - the problem to be solved • Propose features - how the need will be resolved • Requirements are the specific conditions that are imposed on the solution

  14. Problem Domain Needs Features Solution Domain Requirements Question 4

  15. SOFTWARE LIFECYCLE PROCESS MODELS

  16. Waterfall Model • Manufacturing life cycle model • Assumes • multi-stage development cycle • completely separate stages • output of one stage is input for next • each stage complete before next is begun

  17. Requirements Design Coding Testing Maintenance Waterfall Stages

  18. Advantages • Much better than chaos! • Clearly defined stages help with • planning, scheduling • management, organization • accountability, control

  19. Disadvantages • Not very practical (do not know requirements in the beginning) • Customer sees nothing until last step • Change is Anathema

  20. Spiral Model • Incremental • more feedback from customer • Risk analysis • more rigorous analysis of risk at each stage

  21. Spiral Model

  22. Iterative (or Incremental) Approach • Four phases • Inception • Elaboration • Construction • Transition

  23. Iterative(or Incremental) Approach • An iteration is a sequence of activities with an established plan and evaluation criteria, resulting in an executable of some type • Each phase goes under a # of iterations

  24. In an iteration, you walk through all activities Phases Inception Elaboration Construction Transition Business Modeling Requirements Analysis & Design Implementation Test Deployment Configuration Mgmt Workflowsgroup activities logically Management Environment Preliminary Iteration(s) Iter.#1 Iter.#2 Iter.#n Iter.#n+1 Iter.#n+2 Iter.#m Iter.#m+1 Iterations Rational Unified Process Model Process Workflow Support Workflow Question 5

  25. Software Development • Is this a team activity? Why?

  26. Requirements Team Skills • Analyzing the Problem • Understanding User and Stakeholder Needs • Defining the System • Managing Scope • Refining the System Definition • Building the Right System

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