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Table 2: Invariants of Spiral Processes: Name, Rationale, and Variants Invariant {& example} Why invariant Variants 1. Concurrent rather than Avoids premature sequential determination of sequential commitments key artifacts--Ops Concept, Requirements, Plans, Design, Code--in each spiral cycle {One- Second Response Time} 2. Each cycle considers critical stakeholder objectives and constraints, product and process alternatives, risk identification and resolution, stakeholder review, and commitment to proceed {Windows-only COTS} 3. Level of effort on each activity within each cycle driven by risk considerations {Pre-ship Testing} 4. Degree of detail of artifacts produced in each cycle driven by risk considerations {GUI layouts} 5. Managing stakeholder life cycle commitments via the LCO, LCA, and IOC anchor point milestones {Stud Poker Analogy} 6. Emphasis on system and life cycle activities and artifacts rather than software and initial development activities and artifacts {Order Processing} 1a. Relative amount of each artifact developed in each cycle 1b. Number of concurrent mini-cycles in each cycle Avoids commitment to 2a. Choice of risk resolution alternatives that are risky or techniques: prototyping, unacceptable to simulation, modeling, stakeholders benchmarking, reference Avoids wasting effort on checking, etc. unusable alternatives 2b. Level of effort on each activity within each cycle Avoids too little or too much of each activity Avoids overkill or belated risk resolution Avoids too little or too much of each artifact Avoids overkill or belated risk resolution Avoids analysis paralysis, unrealistic expectations, requirements creep, architectural drift, COTS shortfalls or incompatibilities, unsustainable architectures, traumatic cutovers, useless systems Avoids premature suboptimization on hardware, software, or development considerations 3a. Choice of methods used to pursue activities: MBASE/WinWin, Rational RUP, JAD, QFD, ESP, . . . 3b. Degree of detail of artifacts produced in each cycle 4a. Choice of artifact representations (SA/SD, UML, MBASE, formal specs, programming languages, etc.) 5a. Number of spiral cycles or increments between anchor points 5b. Situation-specific merging of anchor point milestones 6a. Relative amount of hardware and software determined in each cycle 6b. Relative amount of capability in each life cycle increment 6c. Degree of productization (alpha, beta, shrink-wrap, etc.) of each life cycle increment 28 CMU/SEI-2000-SR-008
Table 3: Hazardous Spiral Look-Alikes Hazardous Spiral Look-Alike Incremental sequential waterfalls with significant COTS, user interface, or technology risks Sequential spiral phases with key stakeholders excluded from phases Risk-insensitive evolutionary or incremental development Impeccable spiral plan with no commitment to managing risks Insistence on complete specifications for COTS, user interface, or deferred-decision situations Evolutionary development with no lifecycle architecture Purely logical object-oriented methods with operational, performance, or cost risks Invariant Examples 1 One Second Response Time Violation of Waterfall Assumptions 2 Windows-only COTS Excluding Key Stakeholders 3 Pre-ship Testing Risk Insensitivity Section 3.3: Risks of Evolutionary Development 3 (special case of the above) 4 Risk of Precise Specification 5 Section 3.3: Risks of Evolutionary Development 6 Logic-Only OO Designs CMU/SEI-2000-SR-008 29
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