COMP61511(Fall2019)SoftwareEngineeringConcepts

InPracticeWeek1

BijanParsia&ChristosKotselidis< ,@manchester.ac.uk>

(bugreportswelcome!)

bijan.parsiachristos.kotselidis

1 .1

TheFieldSoftwareengineeringaimsto

producesuccessfulsoftwaresystemsviasuccessfuldevelopmentprojects

Programmingisonlyoneaspect!

1 .2

TopicOverviewWelookatdifferenttopics

ThenatureofcomplexsystemsSystemconstruction(coding,debugging,testing,problemdefinition)ProfessionalismandprofessionallifeSocial/ethical/legalissues

(Wemayadjustthetopicsasneededordesired)

1 .3

CourseGoalsThis aimstogivestudentsa

1. astrongconceptualunderstandingofsoftwareengineering2. theabilitytorelatethatconceptualunderstandingtopracticalapplication

3. familiaritywiththesoftwareengineeringscientificandpractionerliterature

sufficienttodriveongoinglearning

courseunit

1 .4

CourseStructureLectures

ActivelearningLabs&Coursework

Makesureyouunderstandthecoursework!Readings

Mostreadingsavailableonline(inoneformoranother)LecturesgobeyondtextsTextsgobeyondlectures

1 .5

TextsPractitioner'stext:

SteveMcConnell,CodeComplete:APracticalHandbookofSoftwareConstructionPhysicalcopiesandavailableasebookin

Researcher'stext:AndyOramandGregWilson(eds),Makingsoftwarewhatreallyworks,andwhywebelieveitPhysicalcopiesandas

Onlinepostsandresearchpapers.

SafariOnline

ebook

1.6

SomeIssuesTheLibrary'se-versionsareratelimited

Limitedconcurrentusersandabout10physicalcopies

1 .7

MitigationsYoucanpurchasethebooks

(£15.92); (£19.89)PrioritiseCodeComplete(forthisclass)

Subscriptionservice10dayfreetrial£39amonth(andcancancel)

CodeComplete MakingSoftware

SafariBooksOnline

1 .8

ANoteOnTheTextsTheyareverygood,but...

...softwareengineeringisnotasettledfield.

Readcriticallyandlookforthemostrecentevidence.

(TheearlychaptersofMakingSoftwarearehelpfulforthis!)

1 .9

AdditionalCoreTextGuidetotheSoftwareEngineeringBodyofKnowledge(SWEBOKGuide)

Free .Notatextbook,butagoodtouchstoneaboutwhataproshouldknowExtensivecoverageandbibilography.Fairlyreadable.Butaguide,notanembodimentoftheBodyofKnowledge

PDF

1.10

AssessmentCoursework(50%)

Eachweek,amixture(notalleveryweek)1. MCQquizzes2. Shortessays3. Individualengineeringassignments

PrecisemarkbreakdownvariesExam(50%)

TakenonlineVerylike1&2

1 .11

Materials&BlackboardAllcoursematerialsareavailable

Weuse forCourseworkOnlineforum

Usethis!Subscribe!Wecareandwanttohelp

Exam

onlinehttp://syllabus.cs.manchester.ac.uk/pgt/COMP61511/Blackboard

1 .12

VariantCircumstancesDisability

Equalityactdefinition:isanyconditionwhichhasasignificant,adverseandlong-termeffectonaperson’sabilitytocarryoutnormalday-to-dayactivities.

Exam&StudysupportGreat,helpfulpeople

DisabilityAdvisoryandSupportService

Feelfreetoconsultacourseinstructoraboutthis!We'rehappytoadvise.

1 .13

VariantCircumstancesatemporaryconditionorsituationwhichhasasignificant,adverseeffectonaperson’sabilitytocarryoutnormalday-to-dayactivities

Helpavailablefrom & &yourGPMedical(mentalorphysical)issuesarenottheonlymitigatingcircumstances!

Mitigatingcircumstances

SSO Counsellingservice

1 .14

ANoteAboutAssistanceEarlyinterventionismoreeffective

Ifyouarehavingchallengesofanysortthesoonerknownbyus,thebetterhandled

ThisisverytrueformitigatingcircumstancesIfsomethingisinterfering,documentit!Thereisa"toolate"here!

Again,whenindoubt,askus.

ALLlateworkishandledbythe ,notus.MitCircscommittee

1 .15

ExpectedConductWeexpectofyou(andourselves)

TobefairmindedTotreateachotherwellToavoidacademicmalpracticeTotakeresponsibilityforcoursedutiesTobeengaged,curious,andactive

IfyouhaveaproblemorissuePleaseraiseitwithusIfthatseemsunhelpful,contactyourcoursetutor

1 .16

AcademicMalpracticeWetakeitveryseriously!

Mostcommonforms:Plagiarism&CollusionThe(few)pointsyoucangetaren'tworthlosingyourdegree!Guardagainstthem!

Don'tcut-paste-modifyQuoteandcitetextCiteideasDonotdiscussassignmentswithotherstudents

Usethediscussionboard!

1 .17

Preliminaries

2.1

WhatIsSoftwareEngineering?Theproductionofsoftwaresystemswhether

"standalone"componentsoflargersystems

Mostsoftwareinteractswithvariousformsofhardwareothersoftwaresystemspeople!

Softwareengineeringisincreasinglyseenasabranchofsystemsengineering

2.2

WhatIsSystemEngineering?Systems engineering is amethodical, disciplined approachfor the design, realization, technical management, operations,andretirementofasystem.—NASASystemEngineeringHandbook

2.3

WhatIsSystemEngineering?A “system” is a construct or collection of differentelements that together produce results not obtainable bythe elements alone. The elements, or parts, can includepeople, hardware, software, facilities, policies, anddocuments;thatis,allthingsrequiredtoproducesystem-levelresults.—NASASystemEngineeringHandbook

2.4

WhatIsSystemEngineering?amethodical,disciplinedapproachforthe

design,realization,technicalmanagement,operations,andretirement

ofasystem.

—NASASystemEngineeringHandbook

2.5

WhatIsSystemEngineering?A“system”isaconstructorcollectionof

differentelementsthattogetherproduce

resultsnotobtainablebytheelementsalone.

Theelements,orparts,[include]...allthingsrequired

toproducesystem-levelresults.

—NASASystemEngineeringHandbook

2.6

(Complex)SystemsSystemresultsareemergent

1. Theproblembeingtacklediscomplex,amorphous,orevolving2. Thereisheterogeneityinthecomponentsandhowtheyinteract3. Thesystemdesigntakesintoaccountthewholelifecycle4. Thusthedesignspaceisverylargeandcomplex

2.7

OneViewOfTheDesignSpaceEvenifwe it:supersimplify

2.8

OneViewOfTheDesignSpaceIt'snotso :simple

2.9

FredBrooks:NoSilverBulletThe complexity of software is in essential property, not anaccidental one. Hence descriptions of a software entity thatabstractawayitscomplexityoftenabstractawayitsessence.

2.10

FredBrooks:NoSilverBulletManyoftheclassicalproblemsofdevelopingsoftwareproductsderived from this essential complexity and its [super]linearincrease[]withsize.

2.11

FredBrooks:NoSilverBulletMuchof the complexity [the software engineer]mustmaster isarbitrarycomplexity,forcedwithoutrhymeorreasonbythemany human institutions and systems to which his interfacesmustconfirm.Thesedifferfrominterfacetointerface,andfromtime to time,not because of necessity but only becausetheyweredesignedbydifferentpeople

2.12

QuestionTime!!TheBoeingDreamlinerrequiresabout

1. 700,000linesofcode.2. 1.7millionlinesofcode.3. 5.7millionlinesofcode.4. 6.5millionlinesofcode.

2 .13

SoftwareCreep(Planes!)Software !takesover

TheF-35 Joint StrikeFighter, scheduled to becomeoperationalin2010,willrequireabout5.7millionlinesofcodetooperateits onboard systems. And Boeing’s new 787 Dreamliner,scheduled to be delivered to customers in 2010, requires about6.5millionlines of softwarecode tooperate itsavionicsandonboardsupportsystems.

2.14

QuestionTime!!Apremium-classautomobileprobablycontains

1. 100,000linesofcode.2. 1millionlinesofcode.3. 10millionlinesofcode.4. 100millionlinesofcode.

2 .15

SoftwareCreep(Cars!)Software !takesover

Theseare impressive amounts of software, yet if youbought apremium-class automobile recently, ”it probably contains closeto100million linesof software code,”... All that softwareexecutes on 70 to 100 microprocessor-based electronic controlunits(ECUs)networkedthroughoutthebodyofyourcar.

2.16

SoftwareCreep(FutureCars!)Software !takesover

Late last year, the business research firm Frost & Sullivanestimated that carswill require200million to300millionlinesofsoftwarecodeinthenearfuture.

2.17

SoftwareCreep(FutureCars!)Software !takesover

Broy estimates that more than 80 percent of carinnovations come from computer systems and thatsoftwarehasbecomethemajorcontributorofvalue(aswellasstickerprice)incars.

2.18

QuestionTime!!Softwarecreepoccursbecause

1. thecostofhardwaregrowsfasterthanthecostofsoftware.2. thecapabilitiesofmechanicalsystemsgrowsslowerthanthecostofsoftware.

3. thecapabilitiesofmechanicalsystemsishardtoimproverelativetothecapabilitiesofsoftware.

4. softwarecanbeupdatedeasily.

2 .19

MillionsOfLinesOfCode!Let'slookatsomecodebasesizes!

AAA

visualisationspreadsheetdiscussion

(Canwebelievetheseestimates?)(Howdoweinterpretthem?)

(WasBrookswrong?)(Weretheseslideswrong?)

2.20

NonComplexSoftwareSystems?Averagingproblem:Writeaprogramthatwillreadinintegersandoutputtheiraverage.Stopreadingwhenthevalue99999isinput.—Soloway

Isaprogramthatsolvesthe"rainfallproblem"1. acomplexsystem?2. partofacomplexsystem?3. asimplesystem?

2.21

Lab1About1hr

We'llplayitabitbyearLabmaterialsareonline

LongURL:

ShortURL:http://studentnet.cs.manchester.ac.uk/pgt/COMP61511/labs/lab1/

bit.ly/wk1lab1

2.22

ProblemComplexity

3.1

FizzBuzzBuzzMostgoodprogrammersshouldbeabletowriteoutonpaperaprogramwhichdoesthisinaunderacoupleofminutes.

Wanttoknowsomethingscary?–themajorityofcompscigraduates can’t. I’ve also seen self-proclaimed seniorprogrammerstakemorethan10-15minutestowriteasolution.

—ImranGhory

3.2

FizzBuzzButIamdisturbedandappalledthatanyso-calledprogrammerwouldapplyforajobwithoutbeingabletowritethesimplestofprograms. That's a slap in the face to anyone who writessoftwareforaliving.

—JeffAtwood

Isthisagoodattitude?

3.3

FizzBuzzUs!29studentsenrolled24ontimesubmissions22.zip(1.jpg,1.py)

4wronglynamed!(e.g.,`Bijan_Parsia_Lab0.zip)3didn'tunziptoadirectory(1alsowrongnamed)16/24=72%!

5were"eyeball"detectablywrong

45%successrate!!!

Let's !look

3.4

FizzBuzzGolf!Wehad5plasyers(outof22submissions)Sizesrangedfrom83(thewinner!)to533Winner!

for i in range(1, 101): print((not i % 3) * "Fizz" + (not i % 5) * "Buzz" or i)

Lastyear's: for i in range(1,101): print('Fizz'[i%3*4:]+'Buzz'[i%5*4:]or i)

3.5

FizzBuzzCritiqueHere'saclueforyou:Idon'tdowellinprogrammingtasksduring interviews, and I've love someone to come into mycommentsandtellmeIcan'tprogrambasedonthisevent.No,I've only faked it while working for Nike, Intel, Boeing, JohnHancock,LawrenceLivermore,andthrough14orsobooks–nottomention6yearsofonlinetechweblogging.

—ShelleyPowers

3.6

FizzBuzzCritique2In fact,you'll finda lotofpeoplewhodon'tnecessarilydowellwhen it comes to programming tasks or other complex testingduringjobinterviews.Why?Becausethepartofyourbrainthatmanagescomplexproblemsolving tasks is the first that'smoreor less scrambled in high stress situations.Themore stress,themorescrambled.Themorestressedweare,themoreournatural defensive mechanisms take over, and the less energyfocusedintohighercognitiveprocesses.

—ShelleyPowers

3.7

FizzBuzzComplexityOfthequestionitself

WhatconstructsdoesFizzBuzzrequire?Whatkindoferrorscan(reasonably)happen?

OftheuseofthequestionWhatcanweconcludeaboutaFizzBuzzfailure?Areenvironmentalfactorssignificant?DoeswidespreadawarenessofFizzBuzzquestionsinvalidatethem?

3.8

TheRainfallProblem(Results)

—DoWeKnowHowDifficulttheRainfallProblemis?

3.9

RainfallComplexity

—TheRecurringRainfallProblem

3.10

RainfallSolutiondef average_rainfall(input_list): # Here is where your code should go total = 0 count = 0 for m in input_list: if m == -999: break if m >= 0: total += m count += 1 # ignore other negatives avg = 0 if count == 0 else total / count return avg

3.11

WatOr"HiddenComplexity"

3.12

FredBrooks:NoSilverWatMuchof the complexity [the software engineer]mustmaster isarbitrarycomplexity,forcedwithoutrhymeorreasonbythemany human institutions and systems to which his interfacesmustconfirm.Thesedifferfrominterfacetointerface,andfromtime to time,not because of necessity but only becausetheyweredesignedbydifferentpeople

3.13

TestingCorrectnessBeware of bugs in the above code; I have only proved itcorrect,nottriedit.—DonKnuth,Figure6:page5ofclassroomnote

4.1

ReallyBewareOfBugs!

—GraceHopper'sBugReport

4.2

DeveloperTestingWecandistinguishbetween

Testingdonebynon-specialists(McConnell:"Developertesting")

Formanyprojects,theonlysort!Testingdoneby(test)specialists

IfyoucompileandrunyourcodeThenyou'vedoneatest!(ormaybetwo!)

Ifonlya"smoke"test

Testingisinescapable;goodtestingtakeswork

4.3

QuestionTime!Ifyoucompileyourcode

1. youhavetesteditforsyntacticcorrectness.2. youhavetesteditforsemanticcorrectness.3. youhavetesteditforboth.4. youhaven'ttesteditatall.

4 .4

WhatIsATest?Atestcase is arepeatable execution situation of a softwaresystem that produces recordable outcomes. A test is aparticularattemptofatestcase

4.5

WhatIsATest?Theoutcomesmaybeexpected

E.g.,weexpectpassing1+1toacalculatortoreturn2Generallybooleanoutcomes(passorfail)

WemighthaveanerrorthatpreventscompletionTheoutcomesmaybemeasurementresults

E.g.,wewanttofindthetimeittakestocompute1+1

4.6

WhatIsATest?(3)Theoutcomesshouldtestifytosomesoftwarequality

E.g.,correctness,butalsoefficiency,usability,etc.A(single)testspecifiesaveryparticularquality

E.g.,correctforagiveninputE.g.,usesXamountofmemoryforthisscenario

Thefundamentalchallengeoftestingisgeneralisability

4.7

GeneralisabilityProblem(1)Testingshowsthepresence,nottheabsenceofbugs.—Edsger W. Dijkstra, Nato Software Engineering Conference,pg161969

4.8

WhatIsATestCase?Atestcaseisaspecifiedinputwithanexpectedoutput;iftheprogram being tested gives, for the given input, an outputequivalent to the expected one then that test has passed;otherwisefailed.

4.9

TerminologyNoteTestandtestcaseareoftenusedinterchangeably

AndinotherloosewaysMostofthetimeitdoesn'tmatterbecauseeasytodistinguish

WeoftentalkaboutatestsuiteortestsetButthisalsomightbesubordinatedtoatestForexample,

"Weused the followingtestsuite tostresstest ourapplication".

4.10

AnatomyOfATest(1)

4.11

GeneralisabilityThreatAtestcase(A):

Goal:CorrectnesstothespecificationInput:apairofintegers,X and YOutput:theintegerthatistheirsum

TestInput:X=1andY=1Expectedoutput:2

TestresultofSystemSispassWhatcanweconclude?

4.12

QuestionTime!FromthetestresultPasstestcaseA,wecanconcludethat:

1. SystemScorrectlyimplementsthespecification.2. SystemScorrectlyimplementsthespecificationforthisinput

3. Both1and24. Neither1nor2

4.13

QuestionTime!FromthetestresultFailtestcaseA,wecanconcludethat:

1. SystemSdoesnotcorrectlyimplementthespecification.2. SystemSdoesnotcorrectlyimplementthespecificationforthisinput

3. Both1and24. Neither1nor2

4.14

AnatomyOfATest(2)

4.15

EnvironmentMattersThe next most significant subset of [Modification Requests(MRs)] were those that concern testing (the testingenvironmentandtestingcategories)—24.8%oftheMRs....itisnot surprising that a significant number of problems areencountered in testing a large and complex real-timesystem...First, thetestingenvironment itself isa largeandcomplex system thatmust be tested. Second, as the real-time system evolves, so must the laboratory testenvironmentevolve.MakingSoftware,pg.459.

4.16

AGoodTestAgoodtestcaseis

partofasuiteoftestcasesunderstandable

i.e.,youcanrelateittothespectothesystembehavior

fitsinwiththetestenvironmentis(giventhesuite)informative

4.17

EnvironmentMatters

4.18

WordCount(wc)wcisaubiquitoussmalltool

GoesbacktoatleastStillinactiveuse

Thiswillbeourgotoexampleforawhile!Esp.inthelab!

1971

4.19

WordCount

4.20

WordCountTestingCreateyourownPythonversionofWCWithaspecificationbasedontheoriginaldoneman wc

doesitcovereverything?howcantestagainsttheexactspec?ReverseEngineeringtotherescue!

4.21

WCReverseEngineeringReverse engineering is the process ofanalyzing a subjectsystem to identify the system's components and theirinterrelationshipsandtocreaterepresentationsofthesysteminanotherformoratahigherlevelofabstraction.-IEEE

4.22

Let'sStartWithSomethingSmallWhataboutanemptyfile?

Spec1:iftheinputofwcisanemptyfile,itreturns0foralloutputsNote:Definedinput,Expectedoutput

4.23

WhatAboutANormalCase?

4.24

BuildingTheSpecificationByreverseengineeringwcwe:

understandbetterthebehaviorofourprogramarebuildingthespecificationdesignourtestcases!

Whatifwebuildnewsoftware?CustomerspecificationAgileorBUFRrequirementsgathering

4.25

DesigningTestsNotatrivialprocessNumerousparameterstofactorinCommoncasevsCornercasesCanwetesteverything?

InprincipleNo,henceappropriatetestselectioniskeytosuccessBewareofTrade-offsTestcoveragevsExecutionTimevsResources

4.26

DoctestDocTestisaunittestingframeworkforPython

Willbeusedduringoutlabsessions!Providesaneasy-to-useandmodularinterfacefor:IsolatedTestingRegressionTestingOrextendedforallkindsoftesting(almost!)

Moreonthelabthisafternoon!

4.27

SimpleExample # Everything is in a docstring!""">>> 1+12>>> 1+1 #Note that the supplied expected answer is *wrong*. This test will fail3>>> [1, 2, 3][1]2"""

# We add the boilerplate to make this module both executable and importable.if __name__ == "__main__": import doctest # The following command extracts all testable docstrings from the current module. doctest.testmod()

4.28

UnitTestingWC>>> import subprocess>>> subprocess.check_output('wc test1.txt', shell=True)b' 10 10 20 test1.txt\n'

4.29

ProductQualities

5.1

Qualities(Or"Properties")Softwarehasavarietyof

Size,implementationlanguage,license...Userbase,usersatisfaction,marketshare...Crashingness,bugginess,performance,functions...Usability,prettiness,slickness...

characteristics

5.2

"Quality"OfSuccessSuccessisdeterminedby

thesuccesscriteriai.e.,thenatureanddegreeofdesiredcharacteristics

whetherthesoftwarefulfilsthosecriteriai.e.,possessesthedesiredcharacteristicstothedesireddegree

5.3

InducingSuccessWhilesuccessisdeterminedbyqualities

thedeterminationisn'tstraightforwardthedeterminationisn'tstrict

forexample,luckplaysarole!itdependsonhowyouspecifythecriticalsuccessfactors

5.4

SoftwareQualityLandscape20.1.CharacteristicsofSoftwareQuality

5 .5

ExternalVs.Internal(RoughThought)Externalqualities:

McConnell:those"thatauserofthesoftwareproductisawareof"Internalqualities:

"non-externalcharacterisitcsthatadeveloperdirectlyexperienceswhileworkingonthatsoftware"

Boundaryvarieswiththekindofuser!

5 .6

ExternalDefinitionExternalqualities:

McConnell:those"thatauserofthesoftwareproductisawareof"Thisisn'tquiteright!

Ausermightbeawareoftheimplementationlangauge"characteristicsofsoftwarethatauserdirectlyexperiencesinthenormaluseofthatsoftware"?

5.7

InternalDefinitionInternalqualities:

"non-externalcharacterisitcsthatadeveloperdirectlyexperienceswhileworkingonthatsoftware"Intuitively,"underthehood"

5.8

External:FunctionalVs.Non-FunctionalFunctional≈Whatthesoftwaredoes

BehaviouralWhatdoesitaccomplishfortheuserPrimaryrequirements

Non-functional≈HowitdoesitQualityofservice

Therecanberequirementshere!Ecologicalfeatures

5.9

KeyFunctional:CorrectnessCorrectness

Freedomfromfaultsin

spec,design,implementation

DoesthejobFulfillsalltheusecasesoruserstories

Implementationanddesigncouldbeperfect,butiftherewasaspecmisunderstanding,ambiguity,orchange,thesoftwarewillnotbecorrect!

5 .10

External:"QualitiesOfService"Usability—cantheusermakeitgoEfficiency—wrttime&spaceReliability—longMTBFIntegrity

Corruption/lossfreeAttackresistance/secure

Robustness—behaveswellonstrangeinput

Allthesecontributetotheuserexperience(UX)!

5 .11

Internal:TestabilityAcriticalproperty!

RelativetoatargetqualityAsystemcouldbe

highlytestableforcorrectensslowlytestableforefficiency

PartlydeterminedbytestinfrastructureHavinggreathooksfortestspointlesswithouttests

5.12

Internal:TestabilityPracticallyspeaking

LowtestabilityblocksknowingqualitiesTest-basedevidenceisessential

5 .13

QualityInteractions:External20.1,CodeComplete

5.14

Coursework!Therearefourbitsofcoursework

Readings(see )andthelabpagesAshortMultipleChoiceQuestion(MCQ)Quiz(Q1)relatedto(someofthe)readingsAshortEssay(SE1)relatedtoareadingAprogrammingassignment(CW1)

materialspage

6.1

Coursework!Q1&SE1aredueatthestartofnextclass(Friat9:00)CW1isdueonThursat19:00<--Thedaybefore!!!Totalof20points

5forQ1and5forSE110forCW1

6.2

PleaseDon'tStress!It'snotalotofwork

SoifyouarelearningPythonyoushouldhavetime!It'spartlyfordiagnosisPartialworkcountsWe'reheretohelp!Don'tleavebeforebeingsureyouknowwhatyou'redoing

6.3

PleaseWorkAlone!It'simportanttofigureoutwhatyoucandoTheseareasmallnumberofpointsandCW1isfairlysimpleWe'reheretohelp!UsetheBlackboardforum!

WewillmonitorDon'tsharecodethereYoucanshare"highleveltips"

6.4