Founda'onsofSo,wareEngineering

Lecture8:ArchitecturalPa0erns,Tac5cs,andEvalua5onClaireLeGoues

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LearningGoals

•  Understandkeypartsofarchitecturalprocess•  Usearchitecturalstylesandtac5csfordesigndecisions•  Makejus5fiedarchitecturaldecisionsfornewsystemsandwithinexis5ngsystems•  Reviewaproposedarchitecture

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Traceability-Defini'on

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"Theabilitytointerrelateanyuniquelyiden5fiablesoAwareengineeringar5facttoanyother,maintainrequiredlinksover5me,andusetheresul5ngnetworktoanswerques5onsofboththesoAwareproductandit'sdevelopmentprocess"–CoEST

TraceabilityinRequirements?

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Traceability

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QualityGoal:HighAvailability

Req.:Shouldrunonredundantservers

Architecture:Faultrecoverywithvo5ng

Faultpreven5on:Regularrestarts

OODesign/Impl.:Vo5ngmechanism,

socketcommunica5on

Test:Killingrandomserversintestsetup

TraceabilityCompliance

•  Traceabilityrequiredinsomedomains(avionics)– WhydoesXpieceofcodeexist?

•  "Enableverifica5onoftheabsenceofundocumentedsourcecodeandverifica5onofthecompleteimplementa5onofthelow-levelrequirements"

•  Linktospecifica5onsandtestprocedures

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TraceabilityandArchitecture•  Architecturelinksqualitya0ributestothehigh-levelandlow-levelsystemdesign

•  Ensuresqualitya0ributesoAennotevenvisibleincode

•  Cost,effort,disciplineneededtocreateandmaintain.– OAenincomplete,incorrect,outdated

•  Developershateit,andoAendonotunderstandtheneed.–  "Unnecessaryevil"

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CaseStudy:TheGoogleFileSystem

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Ghemawat,Sanjay,HowardGobioff,andShun-TakLeung."TheGooglefilesystem."ACMSIGOPSopera/ngsystemsreview.Vol.37.No.5.ACM,2003.

Assump'ons•  Thesystemisbuiltfrommanyinexpensivecommodity

componentsthatoAenfail.•  Thesystemstoresamodestnumberoflargefiles.•  Theworkloadsprimarilyconsistoftwokindsofreads:large

streamingreadsandsmallrandomreads.•  Theworkloadsalsohavemanylarge,sequen5alwritesthat

appenddatatofiles.•  Thesystemmustefficientlyimplementwell-defined

seman5csformul5pleclientsthatconcurrentlyappendtothesamefile.

•  Highsustainedbandwidthismoreimportantthanlowlatency.

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Ghemawat,Sanjay,HowardGobioff,andShun-TakLeung."TheGooglefilesystem."ACMSIGOPSopera/ngsystemsreview.Vol.37.No.5.ACM,2003.

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Ghemawat,Sanjay,HowardGobioff,andShun-TakLeung."TheGooglefilesystem."ACMSIGOPSopera/ngsystemsreview.Vol.37.No.5.ACM,2003.

Quali'es:ScalabilityReliabilityPerformanceCost

Ques'ons

1.  Whatarethemostimportantqualitya0ributesinthedesign?

2.  Howarethosequalitya0ributesrealizedinthedesign?

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Ghemawat,Sanjay,HowardGobioff,andShun-TakLeung."TheGooglefilesystem."ACMSIGOPSopera/ngsystemsreview.Vol.37.No.5.ACM,2003.

Quali'es:ScalabilityReliabilityPerformanceCost

Exercise

FortheGoogleFileSystem,createaphysicalarchitectureviewthataddressesarelevantqualitya0ribute

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Sofarincourse

Requirements

Architecture

Implementa5on

Levelsofabstrac'on•  Requirements–  high-level“what”needstobedone

•  Architecture(High-leveldesign)–  high-level“how”,mid-level“what”

•  OO-Design(Low-leveldesign,e.g.designpa0erns)– mid-level“how”,low-level“what”

•  Code–  low-level“how”

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Whatisarchitecture?

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Architectureasstructuresandrela5ons(theactualsystem)

Architectureasdocumenta5on(representa5onsofthesystem)

Architectureasprocess(ac5vi5esaroundtheothertwo)

ArchitecturalStylesandTac'cs

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Architecturalstyle(paMern)

•  Broadprincipleofsystemorganiza5on•  Describescomputa5onalmodel– E.g.,pipeandfilter,call-return,publish-subscribe,layered,services

•  Relatedtooneofcommonviewtypes– Sta5c,dynamic,physical

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ExampleArchitecturalPaMerns•  Systemorganiza5on– Repositorymodel– Client-servermodel–  Layeredmodel

•  Modulardecomposi5on– Objectoriented–  Func5on-orientedpipelining

•  Controlstyles– Centralizedcontrol– Event-drivensystems

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Architecturalstyle(paMern)

•  Broadprincipleofsystemorganiza5on•  Seereading

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Source:codeproject.org

Architecturalstyle(paMern)

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Source:codeproject.org

Client-serverpaMern

•  Separa5onofclientsandservers– Serversprovideservices;knownand“stable”– Clientsrequestservices;comeandgo

•  Varie5es:synchronous/asynchronous•  Impactonsecurity,performance,scalability•  Examples:TCP,HTTP,X11

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Client

Server

Database

Wheretovalidateuserinput?

Example:YelpApp

Client-serverstyle

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Source:wikimediacommons

Layeredsystem

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Source:eclipse.org

Tieredarchitecture

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ArchitecturalStyle?

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Ghemawat,Sanjay,HowardGobioff,andShun-TakLeung."TheGooglefilesystem."ACMSIGOPSopera/ngsystemsreview.Vol.37.No.5.ACM,2003.

Tac'cs•  Architecturaltechniquestoachievequali5es– More5edtospecificcontextandquality

•  Smallerscopethanarchitecturalpa0erns–  Problemsolvedbypa0erns:“HowdoIstructuremy(sub)system?”

–  Problemsolvedbytac5cs:“HowdoIgetbe0eratqualityX?”

•  Collec5onofcommonstrategiesandknownsolu5ons– ResembleOOdesignpa0erns

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Manytac'csoutthere!

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ExampleTac'cDescrip'on:Record/playback•  Record/playbackreferstobothcapturinginforma5oncrossinganinterfaceandusingitasinputintothetestharness.Theinforma5oncrossinganinterfaceduringnormalopera5onissavedinsomerepositoryandrepresentsoutputfromonecomponentandinputtoanother.Recordingthisinforma5onallowstestinputforoneofthecomponentstobegeneratedandtestoutputforlatercomparisontobesaved.

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ExampleTac'cDescrip'on:Built-inmonitors•  Thecomponentcanmaintainstate,performanceload,capacity,security,orotherinforma5onaccessiblethroughaninterface.Thisinterfacecanbeapermanentinterfaceofthecomponentoritcanbeintroducedtemporarilyviaaninstrumenta5ontechniquesuchasaspect-orientedprogrammingorpreprocessormacros.Acommontechniqueistorecordeventswhenmonitoringstateshavebeenac5vated.Monitoringstatescanactuallyincreasethetes5ngeffortsincetestsmayhavetoberepeatedwiththemonitoringturnedoff.Increasedvisibilityintotheac5vi5esofthecomponentusuallymorethanoutweighthecostoftheaddi5onaltes5ng.

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Secondandmoredetailedthirdedi5onavailableasebookthroughCMUlibrary.

Manytac5csdescribedinChapter5Briefhigh-leveldescrip5ons(about1paragraphpertac5c)

ArchitectureDesignProcess

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Whatisarchitecture?

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Architectureasstructuresandrela5ons(theactualsystem)

Architectureasdocumenta5on(representa5onsofthesystem)

Architectureasprocess(ac5vi5esaroundtheothertwo)

Architecturedesignprocess•  Choosepartorwholesystemtofocuson•  Understandrelevantrequirements•  Chooseanota5on– Typeofview,vocabularyofelements

•  Createadesign– Pa0erns,tac5cs

•  Evaluate•  Govsno-go– Issuesfeedbackintoprocess

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Architecturedesignprocess

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Choosescope Understandrelevantrequirements

Chooseanota5on

Create/refineadesignEvaluate

Source:ACDM,ADD

“Go”

Architecturaldecisions

•  Heartofarchitecture–decidingwhichpathtogo•  Involvetradeoffanalysis•  Represen5ngthealterna5vesclearly–halfofwork

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Architecturaldecisions

•  SoAwarearchitectureisdesign

•  Adecisionisastepintheprocess– Recordra'onale!(notjustdiagrams)– Tradeoffs– Backtracking

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“Engineeringdesignis[…]adecision-makingprocess(oCenitera/ve),inwhichthebasicsciences,mathema/cs,andengineeringsciencesareappliedtoconvertresourcesop/mallytomeetastatedobjec/ve”–ABET

Architecturedesignprocess

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Choosescope Understandrelevantrequirements

Chooseanota5on

Create/refineadesignEvaluate

Source:ACDM,ADD

Architecturaldecisions

•  SoAwarearchitectureisdesign

•  Adecisionisastepintheprocess– Recordra'onale!(notjustdiagrams)– Tradeoffs– Backtracking

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“Engineeringdesignis[…]adecision-makingprocess(oCenitera/ve),inwhichthebasicsciences,mathema/cs,andengineeringsciencesareappliedtoconvertresourcesop/mallytomeetastatedobjec/ve”–ABET

Architectureevalua'on•  Goal:doesthearchitecturesa5sfyrequirements?

•  ATAM–ArchitectureTradeoffAnalysisMethod– Presentrequirements– Presentarchitecture– Analyzearchitecture– Presentresults–risksandnon-risks

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Source:sei.cmu.edu

U'litytree

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Source:arnon.me

Athena–codereviewsystem

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Source:JansenandBosch2005

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Source:JansenandBosch2005

Architecturedesignprocess

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Choosescope Understandrelevantrequirements

Chooseanota5on

Create/refineadesignEvaluate

Source:ACDM,ADD

Challengesofarchitec'ng

•  Describethesystemthatisnotbuiltyet•  Domainknowledgeisessen5al•  Hugespaceofop5ons•  Heavilyreliantonjudgment

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Howmucharchitecture?

•  Designanddocumentwhenneeded,basedonrisk• When:– Beginning– Whenevercircumstanceschange

•  Agile

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Howmucharchitecture?

•  YAGNI•  Risk• Whentostart:– Beforeimplementa5on– Circumstanceschange

• Whentostop:– Well-defined,requirementsaddressed,passesevalua5on

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Source:BoehmandTurner2003

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Studentapplica'onsystem

Source:BoehmandTurner2003

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Mannedspacemissionso,ware

Source:BoehmandTurner2003

Challengesofarchitec'ng

•  Describethesystemthatisnotbuiltyet•  Domainknowledgeisessen5al•  Hugespaceofop5ons•  Heavilyreliantonjudgment

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Summary

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Architectureasstructuresandrela5ons•  Pa0erns•  Tac5cs

Architectureasdocumenta5on•  Views•  Ra5onale

Architectureasprocess•  Decisions•  Evalua5on•  Reconstruc5on•  Agile

References•  Bass,Clements,Kazman.SoAwareArchitectureinPrac5ce,2013.

•  La0anze.Architec5ngSoAwareIntensiveSystems:aPrac55oner’sGuide,2009.

•  Clements,Bachmann,Bass,Garlan,Ivers,Li0le,Merson,Nord,Stafford.Documen5ngSoAwareArchitectures:ViewsandBeyond,2010.

•  BoehmandTurner.BalancingAgilityandDiscipline:AGuideforthePerplexed,2003.

•  JansenandBosch.SoAwareArchitectureasaSetofArchitecturalDesignDecisions,WICSA2005.

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FurtherReadings•  Bass,Clements,Kazman.SoAwareArchitectureinPrac5ce,2013.

•  La0anze.Architec5ngSoAwareIntensiveSystems:aPrac55oner’sGuide,2009.

•  Clements,Bachmann,Bass,Garlan,Ivers,Li0le,Merson,Nord,Stafford.Documen5ngSoAwareArchitectures:ViewsandBeyond,2010.

•  BoehmandTurner.BalancingAgilityandDiscipline:AGuideforthePerplexed,2003.

•  JansenandBosch.SoAwareArchitectureasaSetofArchitecturalDesignDecisions,WICSA2005.

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Levelsofabstrac'on•  Requirements–  high-level“what”needstobedone

•  Architecture(High-leveldesign)–  high-level“how”,mid-level“what”

•  OO-Design(Low-leveldesign,e.g.designpa0erns)– mid-level“how”,low-level“what”

•  Code–  low-level“how”

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Architecturereconstruc'on

•  Goal:describearchitectureofanexis5ngsystemgivenitssourcecode•  Difficulty:levelofabstrac5oninprogramminglanguageistoolow•  Process:– Itera5ve– Interpre5ve– Interac5ve

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Reconstruc'onsteps

•  Extractrawviews– Toolassistance,sta5c&dynamicanalysis

•  Constructadatabase– Aggregatelargevolumesofdata

•  Viewfusion– Synthesizeahypothe5calview

•  Checkforviola5ons15-313SoAwareEngineering66

Architecturereconstruc'on

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•  Itera5ve•  Interpre5ve•  Interac5ve

Reconstruc'onsteps

•  Extractrawviews– Toolassistance,sta5c&dynamicanalysis

•  Constructadatabase– Aggregatelargevolumesofdata

•  Viewfusion– Synthesizeahypothe5calview

•  Checkforviola5ons15-313SoAwareEngineering68

69Source:BCK13