reliability quinn edition 5 chapter 8.ppt

8/18/2019 reliability QUINN Edition 5 Chapter 8.ppt

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Ethics for the Information AgeFifth Edition

by

Michael J. Quinn

Chapter 8:

Computer eliability



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Chapter !"er"ie#

• Introduction

• Data-entry or data-retrieval errors

• Software and billing errors

• Notable software system failures• Therac-25

• Comuter simulations

•

Software engineering• Software warranties



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8.$ Introduction

• Comuter systems are sometimes unreliable " #rroneous information in databases

" $isinterretation of database information

" $alfunction of embedded systems• #ffects of comuter errors

" Inconvenience

" %ad business decisions

" &atalities



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8.% &ata'Entry or &ata'etrie"al

Errors



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(#o )inds of &ata'related Failure

• ( comuteri)ed system may fail becausewrong data entered into it

•

( comuteri)ed system may fail becauseeole incorrectly interret data theyretrieve



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&isfranchised *oters

• November 2+++ general election

• &lorida dis,ualified thousands of voters

•

eason. /eole identified as felons• Cause. Incorrect records in voter database

• Conse,uence. $ay have affected

election0s outcome



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False Arrests

• Sheila ac3son Stossier mista3en for Shirleyac3son " (rrested and sent five days in detention

•

oberto 4ernande) mista3en for anotheroberto 4ernande) " (rrested twice and sent 12 days in ail

• Terry Dean ogan arrested after someone stole

his identity " (rrested five times6 three times at gun oint



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Accuracy of +CIC ecords

• $arch 2++!. ustice Det8 announces &%Inot resonsible for accuracy of NCICinformation

• #9emts NCIC from some rovisions of/rivacy (ct of 1:'

• Should government ta3e resonsibility for

data correctness;



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&ept. of Justice ,osition

• Imractical for &%I to be resonsible fordata0s accuracy

• $uch information rovided by other law

enforcement and intelligence agencies• (gents should be able to use discretion

• If rovisions of /rivacy (ct strictly followed6

much less information would be in NCIC• esult. fewer arrests



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,osition of ,ri"acy Ad"ocates

• Number of records is increasing

• $ore erroneous records → more falsearrests

• (ccuracy of NCIC records more imortantthan ever



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Analysis: &atabase of -tolen *ehicles

• < 1 million cars stolen every year " =wners suffer emotional6 financial harm

" aises insurance rates for all

• Transorting stolen car across a state line " %efore NCIC6 greatly reduced chance of recovery

" (fter NCIC6 nationwide stolen car retrieval

• (t least 5+6+++ recoveries annually due to NCIC•

&ew stories of faulty information causing false arrests• %enefit < harm → Creating database the right action



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8. -oft#are and /illing Errors



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Errors 0hen &ata Are Correct

• (ssume data correctly fed intocomuteri)ed system

• System may still fail if there is an error inits rogramming



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Errors 1eading to -ystem Malfunctions

• >west sent incorrect bills to cell hone customers

• &aulty ?SD( beef rice reorts

• ?8S8 /ostal Service returned mail addressed to /atentand Trademar3 =ffice

• Selling and grammar error chec3ers increased errors

• New @or3 City 4ousing authority overcharged renters

• (bout '5+ California rison inmates mista3enly released



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Errors 1eading to -ystem Failures

• (mbulance disatch system in Aondon

• Chicago %oard of Trade

• %$B limousine

•

aan0s air traffic control system• Aos (ngeles County ?SC $edical Center laboratory

comuter system

• Comair0s Christmas Day shutdown

• %oeing



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Comair Cancelled All Flights on

Christmas &ay2 %334

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(/ /hoto(l %ehrman6 &ile



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Analysis: E'etailer ,osts 0rong

,rice2 efuses to &eli"er

• (ma)on8com in %ritain offered i/a, for Einstead of E25

• =rders flooded in• (ma)on8com shut down site6 refused to

deliver unless customers aid true rice

• Bas (ma)on8com wrong to refuse to fillthe orders;



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ule 5tilitarian Analysis

• Imagine rule. ( comany must always honorthe advertised rice

• Conse,uences " $ore time sent roofreading advertisements

" Comanies would ta3e out insurance olicies

" 4igher costs→ higher rices

" (ll consumers would ay higher rices

" &ew customers would benefit from errors

• Conclusion " ule has more harms than benefits

" (ma)on8com did the right thing



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)antian Analysis

• %uyers 3new :85F mar3down was anerror

• They attemted to ta3e advantage of (ma)on8com0s stoc3holders

• They were not acting in Ggood faithH

•

%uyers did something wrong



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8.4 +otable -oft#are -ystem

Failures



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,atriot Missile

• Designed as anti-aircraft missile

• ?sed in 1::1 ulf Bar to intercet Scud missiles

• =ne battery failed to shoot at Scud that 3illed 27

soldiers• Designed to oerate only a few hours at a time

• Jet in oeration < 1++ hours

• Tiny truncation errors added u

• Cloc3 error of +8!'!! seconds→ trac3ing error of*7 meters



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,atriot Missile Failure

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&igure from SCI#NC# 255.1!'8 Coyright K1::2 by The (merican (ssociation for the (dvancement of Science8 erinted with ermission8



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Ariane 6

• Satellite launch vehicle

• '+ seconds into maiden flight6 roc3et self-destructed " L5++ million of uninsured satellites lost

• Statement assigning floating-oint value to integer raised

e9cetion• #9cetion not caught and comuter crashed

• Code reused from (riane ' " Slower roc3et

" Smaller values being maniulated " #9cetion was imossible



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A(7( 1ong'&istance +et#or

• Significant service disrution " (bout half of telehone-routing switches crashed

" + million calls not ut through

" *+6+++ eole lost all service " (TMT lost revenue and credibility

• Cause " Single line of code in error-recovery rocedure

" $ost switches running same software " Crashes roagated through switching networ3



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A(7( 1ong &istance +et#or Failure

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obot Missions to Mars

• $ars Climate =rbiter " Disintegrated in $artian atmoshere

" Aoc3heed $artin design used #nglish units

" et /roulsion Aab design used metric units

• $ars /olar Aander " Crashed into $artian surface

" #ngines shut off too soon " &alse signal from landing gear



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&en"er International Airport

• %(# built automated baggage handling system

• /roblems " (irort designed before automated system chosen

" Timeline too short " System comle9ity e9ceeded develoment team0s ability

• esults " (dded conventional baggage system

" 1*-month delay in oening airort " Cost Denver L1 million a day



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(oyo -toc E9change

• &irst day of trading for -Com

• $i)uho Securities emloyee mista3enly enteredorder to sell *1+6++ shares at 1 yen6 instead of 1

share at *1+6+++ yen• #mloyee overrides comuter warning

• (fter sell order osted on e9change0s dislay board6$i)uho tried to cancel order several times software

bug caused attemts to fail• $i)uho lost L225 million buying bac3 shares

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&irect ecording Electronic *oting

Machines

• (fter roblems with 2+++ election6 Congress assed4el (merica Oote (ct of 2++2

• 4(O( rovided money to states to relace unchcard voting systems

• $any states used 4(O( funds to urchase directrecording electronic PD#Q voting machines

• %ra)il and India have run national elections usingD# voting machines e9clusively

• In November 2++* 1! of ?8S8 voters used D#voting machines



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&iebold Electronic *oting Machine

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K (/ /hotoogelio Solis



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Issues #ith &E *oting Machines

• Ooting irregularities " &ailure to record votes

" =vercounting votes

" $isrecording votes• Aac3 of a aer audit trail

• Oulnerability to tamering

• Source code a trade secret6 can0t be e9amined

• /ossibility of widesread fraud through maliciousrogramming



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8.6 (herac'%6



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enesis of the (herac'%6

• (#CA and C built Therac-* and Therac-2+

• Therac-25 built by (#CA " /D/-11 an integral art of system

" 4ardware safety features relaced with software " eused code from Therac-* and Therac-2+

• &irst Therac-25 shied in 1:7! "

/atient in one room " Technician in adoining room



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Chronology of Accidents and

AEC1 esponses

• $arietta6 eorgia Pune 1:75Q

• 4amilton6 =ntario Puly 1:75Q

• &irst (#CA investigation Puly-Set8 1:75Q

•

@a3ima6 Bashington PDecember 1:75Q• Tyler6 Te9as P$arch 1:7*Q

• Second (#CA investigation P$arch 1:7*Q

• Tyler6 Te9as P(ril 1:7*Q

• @a3ima6 Bashington Panuary 1:7Q• &D( declares Therac-25 defective P&ebruary 1:7Q



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-oft#are Errors

• ace condition. order in which two or moreconcurrent tas3s access a shared variablecan affect rogram0s behavior

• Two race conditions in Therac-25 software

" Command screen editing

" $ovement of electron beam gun



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ace Condition e"ealed by Fast'

typing !perators

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ace Condition Caused by Counter

olling !"er to ;ero

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,ost Mortem

• (#CA focused on fi9ing individual bugs• System not designed to be fail-safe

• No devices to reort overdoses

•

Software lessons " Difficult to debug rograms with concurrent tas3s

" Design must be as simle as ossible

" Documentation crucial

" Code reuse does not always lead to higher ,uality• (#CA did not communicate fully with

customers



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Moral esponsibility of the

(herac'%6 (eam

• Conditions for moral resonsibility " Causal condition. actions Por inactionsQ caused the

harm

" $ental conditionR (ctions Por inactionsQ intended or willed -=-

R $oral agent is careless6 rec3less6 or negligent

• Therac-25 team morally resonsible

" They constructed the device that caused the harm " They were negligent



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,ostcript

• Comuter errors related to radiationmachines continue to maim and 3illatients

• Investigation by The New York Times

" Scott erome-/ar3s6 New @or3 P2++*Q

" (le9andra n-Charles6 New @or3 P2++*Q

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8.< Computer -imulations

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5ses of -imulations

• Simulations relace hysical e9eriments

" #9eriment too e9ensive or time-consuming

" #9eriment unethical

" #9eriment imossible

• $odel ast events

• ?nderstand world around us

• /redict the future



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-imulations ,redict ,ath and -peed

of =urricanes

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Courtesy of N(S(



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*alidating -imulations

• Oerification. Does rogram correctly imlementmodel;

• Oalidation. Does the model accurately reresent

the real system;• Oalidation methods

" $a3e rediction6 wait to see if it comes true

" /redict the resent from old data

" Test credibility with e9erts and decision ma3ers



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*alidation by Comparing ,redicted

and Actual !utcomes

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Courtesy of Daimler (



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*alidation by >,redicting the ,resent?

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8.@ -oft#are Engineering

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-pecification

• Determine system re,uirements

• ?nderstand constraints

•

Determine feasibility• #nd roducts

" 4igh-level statement of re,uirements

" $oc3-u of user interface " Aow-level re,uirements statement



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&e"elopment

• Create high-level design

• Discover and resolve mista3es6 omissionsin secification

• C(S# tools to suort design rocess• =bect-oriented systems have advantages

• (fter detailed design6 actual rograms

written• esult. wor3ing software system



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*alidation (estingB

• #nsure software satisfies secification

• #nsure software meets user0s needs

• Challenges to testing software

" Noncontinuous resonses to changes in inut " #9haustive testing imossible

" Testing reveals bugs6 but cannot rove none e9ist

•

Test modules6 then subsystems6 then system



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-oft#are Quality Is Impro"ing

• Standish rou trac3s IT roects• Situation in 1::'

" 1! roects cancelled before comletion

" 12 roects had time andor cost overruns " 1* roects comleted on time on budget

• Situation in 2++*

" 1* roects cancelled " 12 roects had time andor cost overruns

" 1! roects comleted on time on budget



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-uccess of I( ,roects !"er (ime

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8.8 -oft#are 0arranties

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-hrin#rap 0arranties

• Some say you accet software Gas isH

• Some offer :+-day relacement or money-bac3 guarantee

• None accet liability for harm caused byuse of software



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Are -oft#are 0arranties EnforceableD

• (rticle 2 of ?niform Commercial Code

• $agnuson-$oss Barranty (ct

•

Step-Saver Data Systems v. WyseTechnology and The Software Link

• ProD! "nc. v. #eiden$erg

•

%ortensen v. Tim$erline Software



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Moral esponsibility of -oft#are

Manufacturers

• If vendors were resonsible for harmful conse,uencesof defects " Comanies would test software more

" They would urchase liability insurance

" Software would cost more " Start-us would be affected more than big comanies

" Aess innovation in software industry

" Software would be more reliable

•

$a3ing vendors resonsible for harmful conse,uencesof defects may be wrong6 but

• Consumers should not have to ay for bug fi9es

reliability quinn edition 5 chapter 8.ppt

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