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COMP61511(Fall2018)SoftwareEngineeringConcepts

InPracticeWeek5

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

(bugreportswelcome!)bijan.parsia christos.kotselidis

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Let'sLookAtSomeCodeAbitoninversionofcontrolAbitonperformanceanalysis

3.1

CreationClasses

3.2

ClassesOnewayofthinkingofaclassisasanabstractdatatypeplusinheritanceandpolymorphism.—McConnell,6.1

(Thereareotherwaysofthinkingaboutaclass!)

3.3

ProblemsClassesSolveA isaproblemthatcreationsolvesReasontoCreateaClass

ModellingRealorabstractobjects

ComplexityManagementReduceorIsolateComplexityHidedetails,limiteffects,groupcontrol

OrganisationGroupfunctionality,managevariants,reuse

Youcanalwaysask:Whatproblem?&Isit(well)solved?

3.4

SOLIDPrinciplesOfClassDesignSynthesisedby :BobMartin

SRP Aclassshouldhaveone,andonlyone,reasontochange.

OCP Youshouldbeabletoextendaclassesbehavior,withoutmodifyingit.

LSP Derivedclassesmustbesubstitutablefortheirbaseclasses.

TheSingleResponsibilityPrincipleTheOpenClosedPrincipleTheLiskovSubstitutionPrinciple

3.5

SOLIDPrinciplesOfClassDesignSynthesisedby :BobMartin

ISP Makefinegrainedinterfacesthatareclientspecific.

DIP Dependonabstractions,notonconcretions.

TheInterfaceSegregationPrincipleTheDependencyInversionPrinciple

3.6

SOLIDPrinciplesCreditPrinciple Creator/Coiner

SRP,ISP,DIP BobMartin

OCP BertrandMeyer

LSP BarbaraLiskov

3.7

ClassRelationsFunctionalityisdividedacrossclasses(SRP,ISP)

Howthoseclassesinteractiscritical(ISP,DPSP)TheyworktogetherInacontrolledway(wehope!)(SRP,ISP)

Thinkunitvs.integrationtesting!Viatheirinterfaces

(Some)Kindsofrelations:1. Is-A(Inheritence)2. Has-A(Composition)3.Works-With(Collaboration)

3.8

InheritanceClassAspecializesClassB

ClassAandBsharesomethingPhysically:Code,variables,interfaces...Conceptually:AisakindofB

LSP:anAcansubstituteforaBCallersdon'thavetoknowthespecialisingbehavior

SubclassesextendSuperclassesAddnewmethods

SubclassesoverrideSuperclassesPolymorphism

Criticalanddangerous

3.9

CompositionAlotmoreiswrittenaboutinheritancethanaboutcontainment,but that's because inheritance is more tricky and error-prone, not because it's better. Containment is the work-horsetechniqueinobject-orientedprogramming.

3.10

Composition(2)ClassBis(partly)madeofClassA

AnotsubstitutableforBCertainlynotconceptually

BdelegatessomeaspectstoAPersonhas-anameLetaNameclassmanageStructureofnames

SeeManipulationofnames

falsehoodsaboutnames

Theworldexhibitsfractalcomplexity

3.11

CollaborationClasseshaveresponsibilitiesIndividualclassesmaynotbeself-sufficientOtherclasseswhichhelpfulfiltheresponsibilitiesarethecollaborators

CollaboratorsmaybecoupledtoagreaterorlessordegreeInheritancegenerallyyieldstighercouplingsCompositiongenerallyyieldsmoremoderatecouplingsUsingcollaboratorservicesgenerallyisevenlooser

LSPloosenscouplingsPersonrequiresName

Oranysubclassthereof

3.12

ReadabilityAndUnderstandabilityReadability:easeofcomprehendingthecodeUnderstandability:easeofcomprehendingthesoftwaresystem

Abstractionistheconnection

Recall

4.1

CreationRoutines

4.2

RoutinesOnewayofthinkingaboutaroutineisasanoperationforanabstractdatatype.

Another way of thinking about a routine is as a (typically)named, invocable, block of code with a designatedfunctionality(orpurpose).

RoutinesnameandencapsulatebehaviorAtafinegrainedlevel

Routinesarethesmallestunitofabstraction

4.3

Routines&ClassesClassespackageroutines

RoutinesprovidetheexternalinterfaceRoutinesprovidetheinternalimplementationMixingthesebreaksencapsulation

Thesetofclassroutines(methods)Definethebehaviouroftheclass

4.4

ProblemsRoutinesSolveThemostimportantreasonforcreatingaroutineistoimprovethe

intellectualmanageabilityofaprogram—McConnell,7,Keypoints

ModellingSingleactionsorservices(verbs)

ComplexityManagementReduceorIsolateComplexityHidedetails,limiteffects,groupbehavior,simplify

OrganisationGroupfunctionality,managevariants,reuse

4.5

WhatIsCohesion?..cohesion is ...the workhorse design heuristic at theindividual-routinelevel.

Forroutines,cohesionreferstohowcloselytheoperationsinaroutinearerelated.—McConnell, .7.2

Ultimately,aroutineisablockofcodeI.e.,aseriesofstatementsI.e.,asequenceofLOC

TheformofrelationdeterminesthetypeofcohesionThestrengthoftherelationdeterminestheamount

Atleast,pairwise

4.6

TheGood:FunctionalCohesionRelation:

contributingtoagivenoperatione.g.,performingacalculationenactingabehaviorprovidingaservice

ThreatstofunctionalcohesionIrrelevantorsuperfluouscodeConfusedoperationspecificationPoorfactoringBook-keepingandauxillarybehaviors

Debuggingcode,logging,etc.

4.7

Non-IdealCohesions:UtilitySequential,Communicational,andTemporal

Maybevalidreasonsforaroutine!Issuesarisewhen

Anon-idealcohesionisconfusedforfunctionalcohesionSeekingnon-idealcohesionbreaksfunctionalcohesion

MitigatingthethreatsEnsureallpertinentoperationsarecaptured

Asroutines!Documentthetargetcohesion

4.8

Non-IdealCohesionsSequential

Relation:orderdependencyanddatasharing(withincompletefunctionalconnection)Problems:concealsoperations,couplesroutines,breaksoperation/routinemapping

CommunicationalRelation:datasharing(butnofunctionalconnection)Problems:Concealsandcouplesoperations

TemporalRelation:"simultaneous"execution(nofunc-conn)Problems:Conceals&confusesops;riskscoupling

4.9

PoorOrNon-CohesionsProcedural

SequencingwithoutdatasharingGoodvariant(?),theorchestrator

LogicalFunctionallyunrelatedoperationswithamastercontrolstructureAndit'sgoodvariant,thedispatcher

"Coincidental"Relation:ExistanceinthesameroutineTheanti-cohesion!

4.10

CohesionBetween...A class is a collection of data and routines that share acohesive,well-definedresponsibility.Aclassmightalsobea collection of routines that provides a cohesive set ofservicesevenifnocommondataisinvolved.—McConnell,6

4.11

CohesionBetween...We'vemostlytalkedaboutinternalcohesion

I.e.,relationsbetweenLOCinsidearoutineRoutinesarebundledinclasses

ToisolatedependenciesEsp.shareddataAlso,implementationneedsAlso,book-keeping

ToformacoherentsetofservicesClassesdeterminetheresponsibilities

Wecanperformsimilarcohesionanalysisoveraclass

4.12

CodeCreationIsProblemSolvingTheproblemwe'retryingtosolveisnotlackofcode

ProblemsolvingisapracticalskillYougetbetteratitthemorethatyoudoit

AlotofproblemsolvingismatchingThereisanexistingsolutionthatyourecallTherearesolutionsthatalmostwork

AndcanbemadetooTherearetechniquesthatarelikelyfruitful

Experiencegoesalongway

5.1

Boehm'sEvidence

FollowingslidesderivedfromMakingSoftware,Chapter10

5.2

ReadingPapersThesepapersarechallenging!

EvenmassagedabitforthepractitionerLotsoftechnicaljargonandtechniquesSummarizingavastliteratureChallengingstatsandpresentations

Don'tpanic!ThesearereadandrereadFirstreadingshouldfocusonkeypointsLaterreadingsshouldfocusontheevidence

5.3

TheRoleOfArchitectureKeychallenge(Boehm,MakingSoftware,Chp10)

Howmuchshouldyouinvestinarchitecture?Analogytobuilding

Wepaythearchitect10%ofthecostofabuildingWeshouldspend10%oftheprojectbudgetonarchitecture

Isthisenough?Howwouldweknow?

Note:statisticallygeneralconclusionsmaynotapplyinyourcase!

5.4

Bohem'sResearchQuestions:"Byhowmuchshouldyouexpectthecostofmakingchangesorfixingdefectstoincreaseasafunctionofprojecttimeorproductsize?"

"Howmuchshouldyouinvestinearlyarchitectingandevidence-basedprojectreviewsbeforeproceedingintoproductdevelopment?"

5.5

EconomiesCommoditymanufacturingexhibitseconomiesofscale

Making1chipmaybemuchmoreexpensivethan1000Theunitcostdiminishesasthenumberofunitsincreases

Softwareend-unitcostsare(canbe)zeroCheaptomakeacopy!

Installation&configurationmaynotbeSofocusonlinesofcodeorbitsoffunctionality

SoftwareexhibitsdiseconomiesofscaleTheunitcostrisesasthenumberofunitsincreases

Potentiallyexponential!Pgs166-167esp.useful

5.6

CostRatiosWhat'stheratioofcosttofixearlyvs.late?

1970s1inrequirementsto≈100postdelivery

19811:100forlargecodebases

But1:5forsmall(2,000-5,000LOC)1996survey

(70-125):12000s

Someevidenceofreductionfrom1:100to1:20Orevenflat(for1millionlinecodebase)

5.7

CostRatios(ForCoursework!)What'stheratioofcosttofixearlyvs.late?

Thinkofyourcoursework!Beforedeployment(akasubmission)

SmallfixesarecheapEsp.inthecurrencyofthecourse,i.e.,points

Afterdeployment(akasubmission)Even"small"fixesareexpensive(orimpossible)

Courseworkbuildsoverthesemester!Soproblemscanbuildup

5.8

TwoStrategiesAvoidlatebugsMakefixinglatebugscheaperFailuretodobothkillstheproject

FailuretodoonemaybemitigatedbytheotherAllouractivitiesshouldaimforthis

Thuswewantarchitecturesthatprecludesomebugsconfinetheeffectsofallbugs

5.9

TwoArchitectureBreakers(Pg376)"20%ofthedefectsaccountfor80%ofthecosts"

"these20%are...duetoinadequatearchitecture..."TwosortsofcostsDirectcostsOpportunitycosts

TwoexamplebigfailurestheOSarchitecturedidn'tsupportfail-overwhenprocessorsfailedlackedakeyfunctionality

assumingallmessagesareshortthusborkingon1millioncharactermessages

5.10

TradeOffsMoreupfrontarch

Costs!Runsriskofoverruns

SincelesstimeforeverythingelsePotentially,gettingarchright

Reducesreworktime

Note,changingrequirementscankillgettingitright

5.11

SweetSpots

5.12

Summary(Pg403)"...thegreatertheproject'ssize,criticality,andstability,the greater the need for validated architecture feasibilityevidence.

"veryverysmalllow-criticalityprojectswithhighvolatility,thearchitectingeffortsmakelittledifference"

Note:Thereareothercostdrivers;checktheassumptions!

6.1

ATouchOfManagement

6.2

ScopeJustafewpoints

SoftwareengineeringisvastJustmanagementisvast

3ManagementLoci1. Technical2. Organisational3. People

Otherpeople!You!(Butweputthisunderprofessionalism)

6.3

TechnicalManagementVersionControlandBackups

EvenforyourownprivatestuffAlwaysForyourdissertationtext,SEs,etc.

ConfigurationSystem,tools,environmentKnowhowtogettoacleansystemAuto

Justenoughdocumentation

6.4

MethodologySeeAgileClass

But!Methodologyisn'tapanaceaProcessdoesn'tensureresults"Simpletounderstand,difficulttomaster"

Copout?Haveamethodology

HoweverlightweightandidiosyncraticConsistentpracticesareimprovable

Firstimprovementoninconsistentpractices:Makethemconsistent!

6.5

OrganisationTakeadynamicview

AnimprovingorganisationisdesirableAgoodorganisationisalsodesirableWithincertainbounds,improvingisbetter

Goodnessvs.FitAnorganisationcanbegoodinmanydimensionsButthewrongfitforyouYouneedtoassessboth

Sometimesa"worse"organisationisabetterfit

6.6

WhatProgrammersAreDoing

What(Novice)ProgrammersAreDoing

Chapter26.NoviceProfessionals:RecentGraduatesinaFirstSoftwareEngineeringJob

6.7

6.8

StrengthsAndWeaknesses"""Amongtheirstrengthsare:

ProgrammingReadingandwritingspecificationsDebugging(persistenceandhypothesisgeneration)

Weaknessesinclude:CommunicationsCognitionOrientation(engagingwithalargecodebaseandpreexistingsoftwareteam)"""

Chapter26.NoviceProfessionals:RecentGraduatesinaFirstSoftwareEngineeringJob

6.9

QuestionAsking"Anoverarchingthemeofnewdevelopers’communicationproblemsis

knowinghowandwhentoaskquestionsofothers.

"Ingeneral,novicesdonotaskquestionssoonenough,andoftenstruggletoaskquestionsatanappropriatelevel."

Chapter26.NoviceProfessionals:RecentGraduatesinaFirstSoftwareEngineeringJob

6.10

(Dis)Orientation"Understandinghowteamnormsdifferfromthoseinacademicsettingsconfusedsomesubjects.""Novicesstruggledtocollect,organize,anddocumentthewiderangeofinformationthattheyneededtoabsorb.""Noviceshaddifficultyorientingthemselvesinthelow-informationenvironmentspresentedbytheirprojectteam,codebase,andresources."Somenovicesfeltwoefullyisolatedfromtheirteams,sometimesnotevenknowingallthemembersoftheirteam,andrarelyknowingwhototalktoaboutcertainissues(orwherethatperson’sofficewas)."

6.11

Techno-SocialSkillsTechnicalskillsareimportant

Butdon'ttypicallydominateTechnicalabilitywon'tmakeyouflourish

thoughtheyhelp!Lowinformationenvironments

RequiremasteryofinfofindingSocialskillskey

UnderstandingthesystemandteamsGoodquestionaskingskills

Thetwoshouldblend

7.1

Professionalism

7.2

ResponsibilitiesToself

Akeysetofresponsibilitiesistoyourself!Youhavethestrongestandmostfundamentalresponsibilitythere!

ToothersInsideyourcircleInsideyourorganisationWithwhomyouhavecommercialobligations"Theprofession"Societyatlarge

7.3

WideResponsibilities"Smallbugs"leadtosecurityfails

Thatcompromisetheprivacyofmillionsorbillions"Smallinefficiencies""

Hugecarbonfootprint"Harmless"businessmodels

Candistort(orenhance!)societyYouaretheproduct

Softwareproblemscaneasilybecomeglobalproblems

7.4

PersonalVirtuesMcConnelltalksofseveral

(InterestingdiscussioninMakingSoftwareaswell)Mostlyaboutwhatmakesagoodprogrammer

OrteammemberKeyonestoconsider

IntellectualHonestyandHumilityCuriosityHabits

7.5

SoftwareEngineeringIsChallenging!Aswe'veseen!

"Insoftwaredevelopment,evenbasicknowledgechangesrapidly.Thepersonwhograduatedfromcollege10yearsafteryoudidprobablylearnedtwiceasmuchabouteffectiveprogrammingtechniques."—McConnell, .

PartofprofessionalismIskeepingup

BlogsCheckoutatextbookeveryfewyearsDedicatedtimetolearning!

33.8

7.6

SoftwareEngineeringIsChallenging!

7.7

SoftwareEngineeringIsChallenging!Aswe'veseen!

"Olderprogrammerstendtobeviewedwithsuspicionnotjustbecausetheymightbeoutoftouchwithspecifictechnologybutbecausetheymightneverhavebeenexposedtobasicprogrammingconceptsthatbecamewellknownaftertheyleftschool"—McConnell, .

Ageism,sexism,ablism(andseveralother-isms)arebigproblemsparticularlyinCompSciandSoftEng

CSandSEalsoshowagenerousspiritLookatmanyopensourcesoftwareprojects

33.8

7.8

AgeismHeadline:

Headline:Headline:Quote:"Facebook’sMarkZuckerbergtoldtheaudience:“Iwanttostresstheimportanceofbeingyoungandtechnical.Youngpeoplearejustsmarter.”

Headline: <--Keyonetoread!

Howthetechindustry'syouthcultisdrivingolderworkerstoplasticsurgery

TheBrutalAgeismofTechIsSiliconValleyAgeistOrJustSmart?

SiliconValley'sdirtysecret-agebias

7.9

WomanInCS:AStrikingGraph

AnatomyofanEnduringGenderGap

7.10

WomanInCS:AnotherGraph

AnatomyofanEnduringGenderGap

7.11

OutrightHarassment

Allsortsofharassment(andthere'salot)Detailssomedisproportionateeffects

"44%ofmenand37%ofwomen"Sexualisedabuse:21%ofwomen/9%menages18to2953%womenages18to29receivedunsolicitedexplicitimages

"35%ofwomen[16%ofmen]...describetheirmostrecentincidentaseitherextremelyorveryupsetting"

TheInternetProblemWeDon'tTalkEnoughAboutOnlineHarassment2017

7.12

ProfessionalismWeconceiveourselvesasaprofession

Seethe or orWehaveprofessionalstandardsWetakeresponsibility

Creativity,spontaneity,funArenotopposedtoprofessionalism!

BCS ACM IEEE

PythonCommunityCodeofConductGNUKindCommunicationsGuideliens

7.13

AimForTheBest

7.14

MakeThingsBetter

8.1

WrapUp

8.2

Thanks!Fourthtimeforme!

SecondtimeforChristos!!

Wehopeyou'velearnedstuff

Wehave!

8.3

CourseworkYou'vedonealot

CW4stilltocome!Let'stalkaboutthereport

8.4

Exam2hrlimitElectronicAfastpersonshouldtake≈1hrFast!≈doesbest

FinalversionstillmustgothroughmoderationSoIcan'tsayfirmlyButexpect

23+somethingMCQs3-5ShortEssay

8.5

MScProjectsProjectbookwillbecomingoutsoon

Pickprojectsthatchallengeyou!Specialconsiderationsifyou'reinterestedinPhDstudies

Threeprojectsfromme(atleast)potentiallyofinterest:CourseworkToolsGeneratingmultiplechoicequestionsbasedondigitalisedclinicalpathwaysLegalTechProjects

8.6

SUPERFUN!WedisHALLOWEEN!!!

Iwillbedoingsomething!Lotsgoingon!

thisweekendattheVictoriaBaths!!!AweekfromMonday!

Remember,RemembertheFifthofNovememberGuyFawkesnight!Awesomefireworksandgiantbonfires!!

Don'tmissitIrecommendHeatonPark(whichisawesomeanwyay)PlattFieldParkiscloser

Coolmovies

https://tinyurl.com/bonfires2018

8.7

THRILLS.....

8.8

....AndCHILLS!!!!!