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Requirements - Why What and How? Sriram Mohan.
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Outline Why ? What ? How ?
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Why Requirements
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Some facts 250 billion dollar industry 31% projects cancelled(money lost 81 billion dollars) 52.7% cost 189% of their original estimates 4
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Biggest Reasons for Project Success and Failure
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Project Failure Lack of user input (13%) Incomplete requirements (12%) Changing requirements (12%)
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Project Success User involvement (16%) Executive management support (14%) Clear statement of requirements (12%)
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Defects by Development Phase Requirements – 31% Design – 25% Coding – 12% Documentation – 16% Bad fixes – 16%
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Cost to Fix Errors 10 Requirements Design Coding Unit Test Acceptance Test Maintenance 1 5 25 50 125 500
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Why ? Requirements errors are likely to be the most common class of error Requirements errors are likely to be the most expensive to fix 11
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What is a Software Requirement?
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1.A software capability needed by the user to solve a problem to achieve an objective 2.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 13
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What is Software Requirements MGMT?
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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. 15
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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 17
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18 Needs Features Requirements Problem Domain Solution Domain
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Software Lifecycle Process Models
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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
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Waterfall Stages Requirements DesignCodingTestingMaintenance
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Advantages Much better than chaos! Clearly defined stages help with – planning, scheduling – management, organization – accountability, control
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Disadvantages Not very practical (do not know requirements in the beginning) Customer sees nothing until last step Change is Anathema
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Spiral Model Incremental – more feedback from customer Risk analysis – more rigorous analysis of risk at each stage 25
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Spiral Model
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Iterative (or Incremental) Approach Four phases – Inception – Elaboration – Construction – Transition 27
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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 28
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Management Environment Business Modeling Implementation Test Analysis & Design Preliminary Iteration(s) Iter. #1 Phases Iterations Iter. #2 Iter. #n Iter. #n+1 Iter. #n+2 Iter. #m Iter. #m+1 Deployment Configuration Mgmt Requirements ElaborationTransitionInceptionConstruction Workflows group activities logically In an iteration, you walk through all activities Process Workflow Support Workflow Rational Unified Process Model
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Team Project Process Modified Waterfall model will be used in 371 You may choose any model you desire during implementation in 372 30
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Software Development Is this a team activity? Why? 31
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Requirements Team Skills 1.Analyzing the Problem 2.Understanding User and Stakeholder Needs 3.Defining the System 4.Managing Scope 5.Refining the System Definition 6.Building the Right System
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