Software Development and Lifecycles CS201 Fall 2004 Week 11

Software Development Software Development and Lifecyclesand Lifecycles

CS201CS201

Fall 2004Fall 2004

Week 11Week 11

Reading for todayReading for today

Extreme Software EngineeringExtreme Software Engineering chapter 8 – acceptance testingchapter 8 – acceptance testing

skim part about fit frameworkskim part about fit framework

QuestionsQuestions be prepared to talk about how your be prepared to talk about how your

team has dealt with acceptance testingteam has dealt with acceptance testing bring in a concrete examplebring in a concrete example

What’s the Problem?What’s the Problem?

Software costs are increasing as Software costs are increasing as hardware costs decline.hardware costs decline.

Many software development Many software development disasters:disasters:

Many failures attributed to softwareMany failures attributed to software Cost of failure becoming very high:Cost of failure becoming very high:

Software Failures or Software Failures or DisastersDisasters

Shuttle launch Shuttle launch anomalyanomaly


Outages of AT&T Outages of AT&T Long Distance Long Distance switchesswitches


Ariane 5 launch explosion, 4 June Ariane 5 launch explosion, 4 June 19961996 http://www.esrin.esa.it/htdocs/tidc/Press/http://www.esrin.esa.it/htdocs/tidc/Press/

Press96/ariane5rep.htmlPress96/ariane5rep.html


« ESA« ESA

The page you are looking for is not The page you are looking for is not present anymore or is temporarily present anymore or is temporarily unavailable. Please choose one of unavailable. Please choose one of the topics below and update your the topics below and update your bookmarks accordingly.bookmarks accordingly.

http://www.esa.int/export/esaCP/index.html

Software Failures or Software Failures or Disasters (cont’d)Disasters (cont’d)

Social Security disasterSocial Security disaster

We have a “software crisis” We have a “software crisis” (1968)(1968)

““Software Engineering” Software Engineering” An “early” study of “problem” DOD An “early” study of “problem” DOD

projectsprojects 47% unusable47% unusable 29% never delivered29% never delivered ONLY 19% of software useful after extensive ONLY 19% of software useful after extensive

reworkrework

Definition of Software Definition of Software EngineeringEngineering

Fairley’s:Fairley’s: technologicaltechnological and and managerialmanagerial discipline discipline concernedconcerned

systematic productionsystematic production maintenancemaintenance software products software products developed and developed and modifiedmodified on timeon time within cost estimateswithin cost estimates..

Definition of Software Definition of Software EngineeringEngineering

Engineering versus science:Engineering versus science: Production,Production, practical practical qualityquality maintenancemaintenance reusereuse standardsstandards teamsteams managementmanagement etcetc

SW Engineering Is and Is SW Engineering Is and Is Not...Not...

It is (or should be):It is (or should be): EngineeringEngineering Building Building Modifying Modifying

A systematic, careful, disciplined, A systematic, careful, disciplined, scientific activityscientific activity

SW Engineering Is and Is SW Engineering Is and Is Not...Not...

It is not:It is not: Just building Just building

small systemssmall systems new systems.new systems.

Hacking/debugging until it works.Hacking/debugging until it works. Easy, simple, boring or pointlessEasy, simple, boring or pointless

One Way to Think About ItOne Way to Think About It

Build a bridge to cross a small creekBuild a bridge to cross a small creek Build a bridge across the Golden GateBuild a bridge across the Golden Gate What’s different?What’s different?

project size project size number of peoplenumber of people lengthlength riskrisk economicseconomics

"Writing Programs""Writing Programs"

““Programming in the small”Programming in the small” ““Programming in the large”Programming in the large”

Software Lifecycle and Software Lifecycle and PhasesPhases

birth to deathbirth to death Phases might include:Phases might include:

Requirements phaseRequirements phase Specification phaseSpecification phase Design phaseDesign phase Implementation phaseImplementation phase Integration or “testing” phaseIntegration or “testing” phase Maintenance phaseMaintenance phase

Analogy: SE is like Analogy: SE is like ConstructionConstruction

Think about how buildings come to Think about how buildings come to be:be: RequirementsRequirements ArchitectureArchitecture ConstructionConstruction

Differences?Differences? MaintenanceMaintenance DesignDesign

Requirements, Design, and Requirements, Design, and ImplementationImplementation

RequirementsRequirements whatwhat WhoWho not "here is the solution"not "here is the solution"

DesignDesign howhow modelmodel evaluationevaluation

Three Key Elements in SEThree Key Elements in SE

Process:Process: life-cycle, management, assessment, life-cycle, management, assessment,

quality assurancequality assurance Method:Method:

Problem solving approachesProblem solving approaches Tools:Tools:

Software that supports methods and/or Software that supports methods and/or processesprocesses

Example: Process, Method, Example: Process, Method, ToolsTools

Unit testingUnit testing Process: How it’s to be done? When, Process: How it’s to be done? When,

who, etc.?who, etc.? Documents:Documents: Who?Who? How do we verify (check) that its been How do we verify (check) that its been

done?done?

Example: Process, Method, Example: Process, Method, Tools (cont’d)Tools (cont’d)

Method: What approach to be used?Method: What approach to be used? Example: Black box testingExample: Black box testing

Tools: Software approach for Tools: Software approach for process and methodsprocess and methods

SE Can’t Ignore Economic SE Can’t Ignore Economic AspectsAspects

New techniques, tools, etc. must be New techniques, tools, etc. must be worth itworth it

Example: Coding method CMExample: Coding method CMnewnew is is 10% faster than currently used 10% faster than currently used method CMmethod CMold. old. Should it be used?Should it be used? Common sense answer Common sense answer Software Engineering answer Software Engineering answer

Risk and SW EngineeringRisk and SW Engineering

Many problems arise because of riskMany problems arise because of risk Example problemsExample problems Good SEs work to manage and Good SEs work to manage and

reduce riskreduce risk

Managing RiskManaging Risk

Risk areasRisk areas How to identify, manage and reduce How to identify, manage and reduce

riskrisk Prototyping, ...Prototyping, ...

Reminder: Lifecycle, PhasesReminder: Lifecycle, Phases

Phases might include:Phases might include: Requirements phaseRequirements phase Specification phaseSpecification phase Design phaseDesign phase Implementation phaseImplementation phase Integration or “testing” phaseIntegration or “testing” phase Maintenance phaseMaintenance phase

Relative Cost Per PhaseRelative Cost Per Phase

6%

5%

7% 8%

Maintenance 67%

Integration

Modulecoding

Moduletesting

Design

Specification (Analysis)5%

2%Requirements

Why Is Maintenance Why Is Maintenance Expensive?Expensive?

Good software is maintained. Good software is maintained. Different types of maintenanceDifferent types of maintenance

Corrective [20%]Corrective [20%] Perfective [60%]Perfective [60%] Adaptive [20%]Adaptive [20%]

Maintenance matters and costs even if Maintenance matters and costs even if released code has zero defects!released code has zero defects!

Source of Defects by PhaseSource of Defects by Phase

60 to 70 % of faults are from specification or design60 to 70 % of faults are from specification or design Data of Kelly, Sherif, and Hops [1992]Data of Kelly, Sherif, and Hops [1992]

1.9 faults per page of specification1.9 faults per page of specification 0.9 faults per page of design0.9 faults per page of design 0.3 faults per page of code0.3 faults per page of code

Data of Bhandari et al. [1994]:Data of Bhandari et al. [1994]:Faults at end of design phase of new version of productFaults at end of design phase of new version of product 13% of faults from previous version of product13% of faults from previous version of product 16% of faults in new specifications16% of faults in new specifications 71% of faults in new design71% of faults in new design

Cost to Correct Fault Cost to Correct Fault According to PhaseAccording to Phase

Requirements

Design IntegrationSpecification

(Systems Analysis)

Implementation Maintenance

1 2 4 1030

200

3

Planning

100

50

150

200

Ap

pro

xim

ate

re

lativ

e c

ost

to

de

tect

an

d c

orr

ect

a f

au

lt368

52

1994 data [Kan et al.]1981 data [Boehm]

250

300

350

Life-cycle Process ModelsLife-cycle Process Models

Process: Process: done by development organizationdone by development organization the the events or tasksevents or tasks sequencesequence

OrganizationsOrganizations want process that is: want process that is: a well-defineda well-defined well-understoodwell-understood repeatablerepeatable

Various Models for SW Various Models for SW LifecylesLifecyles

““Historical Models”Historical Models” Waterfall, Spiral modelsWaterfall, Spiral models

Government StandardsGovernment Standards DoD ,FAA DoD ,FAA

Corporate “Standards” or common Corporate “Standards” or common practicespractices roll your ownroll your own

Why Learn About Process Why Learn About Process Now?Now?

There are general principles of about:There are general principles of about: What we do at various stages of SW What we do at various stages of SW

developmentdevelopment How to inject quality into SWHow to inject quality into SW How to avoid early problems that cause How to avoid early problems that cause

huge problems laterhuge problems later Recognize that SE is not just writing Recognize that SE is not just writing

codecode

Traditional ‘waterfall’ Traditional ‘waterfall’ lifecyclelifecycleRequirements

analysis

Design

Code

Test

Maintenance

A Quality-A Quality-based based ViewView

The Spiral ModelThe Spiral Model

Is the Spiral Model the Is the Spiral Model the Answer?Answer?

MaybeMaybe Original study: Original study:

Intended for internal development Intended for internal development large systemslarge systems

But, the spiral model is importantBut, the spiral model is important HistoryHistory illustrativeillustrative

Other Model: Agile Process Other Model: Agile Process ModelsModels

Counters "heavyweight" processesCounters "heavyweight" processes XP :“a deliberate and disciplined XP :“a deliberate and disciplined

approach to software approach to software development.”development.” good for risky projectsgood for risky projects EmphasizesEmphasizes

pair-programmingpair-programming test-first, then codetest-first, then code what else?what else?

Final Thoughts on Process Final Thoughts on Process ModelsModels

Every organization Every organization does havedoes have a a processprocess

People have strong feelings on this People have strong feelings on this subject about what works!subject about what works!

(IMHO) There is no “silver bullet” (IMHO) There is no “silver bullet” here.here.