Software Life-cycle Models

Miscellaneous Stuff  



anyone new to the class? Assignment 1 project website and proposal due next class (Thursday)

Project Stuff  

Team issues Proposal issues – Project title – Team members (skills, anticipated role within and contributions to the project) – Project website URL – Objectives of project – Description of project (why do you want to do it, what features do you anticipate it will have, anticipated lifecycle model, anticipate language(s), special needs)



Website issues – Title, names (contact info), meeting summaries, docs

CHAPTER 3

SOFTWARE LIFE-CYCLE MODELS

Software Life-Cycle Models  

Life-cycle model The steps through which the product progresses – – – – – – –

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

Overview         

Build-and-fix model Waterfall model Rapid prototyping model Incremental model Extreme programming Synchronize-and-stabilize model Spiral model Object-oriented life-cycle models Comparison of life-cycle models

Build and Fix Model

Build and Fix Model 

Problems – No specifications – No design





Totally unsatisfactory Need life-cycle model – “Game plan” – Phases – Milestones

Waterfall Model (contd)

Waterfall Model (contd) 

Characterized by – Feedback loops – Documentation-driven



Advantages – Documentation – Maintenance easier



Disadvantages – Specifications

Rapid Prototyping Model  

Linear model “Rapid”

Three Key Points  



Do not turn into product Rapid prototyping may replace specification phase—never the design phase Comparison: – Waterfall model—try to get it right first time – Rapid prototyping—frequent change, then discard

Waterfall and Rapid Prototyping Models 

Waterfall model – Many successes – Client needs



Rapid prototyping model – Not proved – Has own problems



Solution – Rapid prototyping for requirements phase – Waterfall for rest of life cycle

Incremental Model 

Divide project into builds

Incremental Model (contd) 

Waterfall, rapid prototyping models – Operational quality complete product at end



Incremental model – Operational quality portion of product within weeks

  



Less traumatic Smaller capital outlay, rapid return on investment Need open architecture—maintenance implications Variations used in object-oriented life cycle

Incremental Model (contd)

Incremental Model (contd) 

More risky version—pieces may not fit

Extreme Programming        

Somewhat controversial new approach Stories (features client wants) Estimate duration and cost of each story Select stories for next build Each build is divided into tasks Test cases for task are drawn up first Pair programming Continuous integration of tasks

Unusual Features of XP 

 

 

Computers are put in center of large room lined with cubicles Client representative is always present Cannot work overtime for 2 successive weeks No specialization Refactoring

XP Project

XP Iteration

XP Development

XP Coding

Evaluating XP  



XP has had some successes Good when requirements are vague or changing Too soon to evaluate XP

Synchronize-and Stabilize Model  

  

Microsoft’s life-cycle model Requirements analysis—interview potential customers Draw up specifications Divide project into 3 or 4 builds Each build is carried out by small teams working in parallel

Synchronize-and Stabilize Model (contd) 

 

At the end of the day—synchronize (test and debug) At the end of the build—stabilize (freeze build) Components always work together – Get early insights into operation of product

Spiral Model 

Simplified form – Waterfall model plus risk analysis



Precede each phase by – Alternatives – Risk analysis



Follow each phase by – Evaluation – Planning of next phase

Simplified Spiral Model 

If risks cannot be resolved, project is immediately terminated

Full Spiral Model (contd)

Analysis of Spiral Model 

Strengths – Easy to judge how much to test – No distinction between development, maintenance



Weaknesses – For large-scale software only – For internal (in-house) software only

Conclusions    

Different life-cycle models Each with own strengths Each with own weaknesses Criteria for deciding on a model include – – – –



The organization Its management Skills of the employees The nature of the product

Best suggestion – “Mix-and-match” life-cycle model

Object-Oriented Life-Cycle Models 

Need for iteration within and between phases – – – –



Fountain model Recursive/parallel life cycle Round-trip gestalt Rational Unified Process (RUP)

All incorporate some form of – Iteration – Parallelism – Incremental development

Rational Unified Process  

Commercial product from IBM http://www.rational.com/rup/

RUP 

Four cycles – – – – –

inception elaboration construction transition each followed by a major milestone

RUP: Inception Phase 

Purpose – establish the business case and define the project scope



Selected deliverables – – – – – – –

A vision document An initial use-case model An initial project glossary An initial business case An initial risk assessment A project plan One or more prototypes

RUP: Lifecycle Objectives Milestone    

Stakeholder buy-in Requirements understanding Credibility of estimates Prototype evaluation

RUP: Elaboration Phase 

Purpose – analyze problem, establish a sound architecture, develop a project plan, and eliminate high risk elements

 

Hardest phase Selected deliverables – A use-case model – An architecture description – A development plan

RUP: Lifecycle Architecture Milestone    



Is the vision stable? Is the architecture stable? Is the plan detailed enough? Does everyone agree the the plan can achieve the vision? Re-evaluate estimates

RUP: Construction Phase 

Purpose – develop remaining components and into them into the product

 

Should be incremental Deliverables – the software product – the user manuals – a description of the current release

RUP: Initial Operational Capability Milestone 



Is the product stable and mature enough for users? All are stakeholders ready for release to users?

RUP: Transition Phase 

Purpose – to transition the product to the user community



Selected objectives – – – –

beta testing training roll-out to marketing, distribution, and sales achieving final product baseline as rapidly and cost effectively as practical

RUP: Product Release Milestone 

Is the user satisfied?

RUP: Iteration 

Product release may coincide with the inception phase for the next cycle

Book Assignment 

Read chapter 3 – Problems 3.5, 3.6, 3.7, 3.8 – Follow (AND READ) the guided tour at http://www.extremeprogramming.org » DEMO

– Describe what you would like and not like if you worked in an organization that used extreme programming. – Due: February 3rd

Project Assignment  

Website Proposal