Life Cy Cycle Model

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Software Life-Cycle Models

Hans Van Vliet, Software Engineering: Principles and Practices, 3rdedition, Wiley 2008. (Chapter 3)

Eric J. Braude, Software Engineering, An Object-OrientedPerspective, Wiley, 2001. (Section 2.4. Identifying and retiring risks)

Roger S. Pressman, Software Engineering, A Practitioners Approach, 6th edition, McGraw Hill, 2005. (Chapter 25. RiskManagement)


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Software Life-Cycle Models

Life-cycle model (formerly, process model ) The steps through which the product

progresses Requirements phase Specification phase Design phase Implementation phase Integration phase Maintenance phase Retirement

Q: In what order to perform these steps?

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Many Life-Cycle Models

Several dimensions Sequential vs. iterative Whole vs. incremental Elaborative vs. transformational Use of prototype

Examples Waterfall, Rapid prototyping, Incremental, Spiral,

Model-driven, Feature-driven, Unified Process(UP), Extreme Programming (XP),

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Build and Fix Model

Problems No specifications No design

Totally unsatisfactory Need life-cycle model

Game plan Phases

Milestones

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Waterfall Model Characterized by

Feedback loops Documentation-driven Operational product at end

Advantages Documentation Maintenance may be easier

Disadvantages Customer may not be aware of

what getting Costly when discrepancy found

in later stages Sometimes freezes part of

development May lead to badly structured

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Rapid Prototyping Model(Throwaway)

Determine needs ofcustomer

Refine with interaction ofcustomers

Experiment with parts notunderstood Prototype system poorly

structured Operational product at end

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Evolutionary Prototyping

Process not visible (needdeliverables)

Need highly skilled team

Appropriate Small teams Part of system not well

understood Short lifecycle system

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Problem description(outline)

Specification Development Validation

Initial version Intermediate version Final version

Concurrentactivities


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Incremental Model

Divide project into builds Operational quality portion

of product within weeks Smaller capital outlay,

rapid return on investment Need open architecture

maintenance implications Requires skilled

developers

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Incremental Model (Variation)

More risky version pieces may not fit

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Transformation Model

Viewed as a sequence of steps that transforms a specificationinto an implementation

Use of formal specifications/models and transformation rules Correctness by construction program correctness proof E.g., Model-driven development (MDD)

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Transformation/optimization

Requirementsanalysis andspecification

Developmenthistory

Reusablecomponents

Requirements Formalspecifications

Formal specifications(lower level)

Decisions, rationaleand trans. rules


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Spiral Model

Keys: risk analysis and evaluation Simplified form: Waterfall model

plus risk analysis

Precede each phase by Alternatives Risk analysis

Follow each phase by Evaluation Planning of next phase

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Simplified Spiral Model

Focus on eliminating errors early Examines level of effort Accommodates growth and

change (evolution) Restrictions

In-house development (notcontracted)

Good for large-scale systems Requires training in risk

analysis and resolution

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Full Spiral Model (contd)

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Risk

A risk is something that may occur in the course of aproject, and which, under the worst outcome, would affectit negatively and significantly [Braude 2001, Section 2.4].

Two types:

Those that can be avoided or worked around Those cannot be avoided

Problems are those risks that have not been identified.Risks must be managed!

Risk retirement is process whereby risks are reduced oreliminated.

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Risk Management Activities

Identification Mindset: try to continually identify risks Write down concerns and press all team members to think of

moreRetirement planning Outline the steps that can be taken to retire the risk.Prioritization Options: l ikelihood (10 most likely), i mpact (10 most impact),

r etirement c ost (10 highest cost)

Formula: (11 - l ) (11 - i ) rc Lowest is first to addressRetirement or mitigation

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Types of Risks (Pressman 2005, Chapter 25)

Generic (every project) Product size Business impact (constraints imposed by mgmt) Customer characteristics Process definition Development environment Technology to be built

Staff size and experience Product-specific (characteristics of product)

Examples?

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Example Risks

Underestimation of sizeTime lag in learning new toolsLack of top management commitment

Personnel resignChanging scope and/or objectivesTechnical breakthroughs change in product

Unrealistic schedulePersonnel lack required knowledge or skills

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Feature Driven Development (FDD)

Develop an

OverallModel

Build aFeature List Plan by

Feature

Design byFeature Build by

Feature

1) Selection of domainexperts and development

teams2) Completion of

requirements definition byguidance team

Entry Criteria

Completion of:

a) the object model(class, sequencediagrams andexplanatory notes)b) Interview Reportc) Feasibility Reportd) Use case scenarios

Exit Criteria

Completion of thedevelop an overall

model process

Entry Criteria

Completion of thebuild a feature list

process

Completion of theplan by feature

process

Completion of thedesign by feature for

each of the selectedfeatures

Entry CriteriaEntry Criteria

Entry Criteria

Completion of:

a) feature list, including alist of major feature setsand a list of featureswithin each feature setb) GUIc) Modelsd) Requirements

Completion of:

a) development plan,consisting feature setswith completion dates

Completion of:

a) design package,comprising a designdocument, referencedrequirements in the form ofdocuments, memos,supporting documentation,design alternatives, latestobject model, class andmethod prologues, to dotask list on affected classesfor each team members

Completion of:

a) development ofone or morefeatures (client-valued functions)

Exit CriteriaExit Criteria

Exit CriteriaExit Criteria

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Exam Questions

What is Extreme Programming? What are the advantages and disadvantages

of using Extreme Programming as

development model?

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Documents

Life Cy Cycle Model