Object-Oriented and Classical Software Engineering

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Slide 3.1

Object-Oriented and

Classical Software

Engineering

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Slide 3.2

CHAPTER 3

SOFTWARE

LIFE-CYCLE

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Slide 3.3

Overview

z Build-and-fix model z Waterfall model

z Rapid prototyping model z Incremental model

z Extreme programming

z Synchronize-and-stabilize model z Spiral model

z Object-oriented life-cycle models

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Slide 3.4

Software Life-Cycle Models

z Life-cycle model (formerly, process model)

z The steps through which the product progresses

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

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Slide 3.5

Build and Fix Model

z Problems – No specifications – No design z Totally unsatisfactory z Need a life-cycle model – “Game plan” – Phases – Milestones

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Slide 3.6

Waterfall Model

z Characterized by – Feedback loops – Documentation-driven z Advantages – Documentation – Maintenance easier z Disadvantages – Specification document

» Joe and Jane Johnson

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Slide 3.7

Rapid Prototyping Model

z Linear model z “Rapid”

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Slide 3.8

Three Key Points

z Do not turn the rapid prototype into the product z Rapid prototyping may replace the

specification phase—never the design phase

z Comparison:

– Waterfall model—try to get it right the first time

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Slide 3.9

Waterfall and Rapid Prototyping Models

z Waterfall model

– Many successes

– Client’s needs

z Rapid prototyping model

– Not proved

– Has its own problems

z Solution

– Rapid prototyping for the requirements phase

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Slide 3.10

Incremental Model

z Divide project

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Slide 3.11

Incremental Model (contd)

z Waterfall, rapid prototyping models

– Operational quality complete product at end

z Incremental model

– Operational quality portion of product within weeks

z Less traumatic

z Smaller capital outlay, rapid return on investment z Need open architecture—maintenance

implications

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Slide 3.12

Incremental Model (contd)

z Problems

– Build-and-fix danger

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Slide 3.13

Incremental Model (contd)

z More risky version—pieces may not fit

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Slide 3.14

Extreme Programming

z Somewhat controversial new approach z Stories (features client wants)

z Estimate duration and cost of each story z Select stories for next build

z Each build is divided into tasks

z Test cases for a task are drawn up first z Pair programming

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Slide 3.15

Unusual Features of XP

z Computers are put in the center of a large

room lined with cubicles

z A client representative is always present z Cannot work overtime for 2 successive

weeks

z No specialization z Refactoring

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Slide 3.16

Evaluating XP

z XP has had some successes

z Good when requirements are vague or changing z Too soon to evaluate XP

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Slide 3.17

Synchronize-and Stabilize Model

z Microsoft’s life-cycle model

z Requirements analysis—interview potential

customers

z Draw up specifications

z Divide project into 3 or 4 builds

z Each build is carried out by small teams

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Slide 3.18

Synchronize-and Stabilize Model (contd)

z At the end of the day—synchronize (test and

debug)

z At the end of the build—stabilize (freeze build) z Components always work together

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Slide 3.19

Spiral Model

z Simplified form

– Waterfall model plus risk analysis preceding each phase

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Slide 3.20

Simplified Spiral Model

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Slide 3.21

A Key Point of the Spiral Model

z If all risks cannot be resolved, the project is

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Slide 3.22

Full Spiral Model

z Precede each phase by

– Alternatives

– Risk analysis

z Follow each phase by

– Evaluation

– Planning of next phase

z Radial dimension: cumulative cost to date

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Slide 3.23

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Slide 3.24

Analysis of Spiral Model

z Strengths

– It is easy to judge how much to test

– No distinction is made between development, maintenance

z Weaknesses

– For large-scale software only

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Slide 3.25

Object-Oriented Life-Cycle Models

z Need for iteration within and between phases

– Fountain model

– Recursive/parallel life cycle

– Round-trip gestalt

– Unified software development process

z All incorporate some form of

– Iteration

– Parallelism

– Incremental development Danger

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Slide 3.26

Fountain Model

z Overlap (parallelism) z Arrows (iteration) z Smaller maintenance circle

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Slide 3.27

Conclusions

z Different life-cycle models

– Each with its own strengths

– Each with its own weaknesses

z Criteria for deciding on a model include:

– The organization

– Its management

– Skills of the employees

– The nature of the product