Chapter4:UnderstandingQualityAttributes?LenBass,PaulClements,RickKazman,distributedunderCreativeCommonsAttributionLicenseChapterOutlineArchitectureandRequirementsFunctionalityQualityAttributeConsiderationsSpecifyingQualityAttributeRequirementsAchievingQualityAttributesthroughTacticsGuidingQualityDesignDecisionsSummary

?LenBass,PaulClements,RickKazman,distributedunderCreativeCommonsAttributionLicenseArchitectureandRequirementsSystemrequirementscanbecategorizedas:Functionalrequirements.Theserequirementsstatewhatthesystemmustdo,howitmustbehaveorreacttorun-timestimuli.Qualityattributerequirements.Theserequirementsannotate(qualify)functionalrequirements.Qualificationmightbehowfastthefunctionmustbeperformed,howresilientitmustbetoerroneousinput,howeasythefunctionistolearn,etc.Constraints.Aconstraintisadesigndecisionwithzerodegreesoffreedom.Thatis,it’sadesigndecisionthathasalreadybeenmadeforyou.?LenBass,PaulClements,RickKazman,distributedunderCreativeCommonsAttributionLicenseFunctionalityFunctionalityistheabilityofthesystemtodotheworkforwhichitwasintended.Functionalityhasastrangerelationshiptoarchitecture:functionalitydoesnotdeterminearchitecture;givenasetofrequiredfunctionality,thereisnoendtothearchitecturesyoucouldcreatetosatisfythatfunctionalityfunctionalityandqualityattributesareorthogonal?LenBass,PaulClements,RickKazman,distributedunderCreativeCommonsAttributionLicenseQualityAttributeConsiderationsIfafunctionalrequirementis"whentheuserpressesthegreenbuttontheOptionsdialogappears”:aperformanceQAannotationmightdescribehowquicklythedialogwillappear;anavailabilityQAannotationmightdescribehowoftenthisfunctionwillfail,andhowquicklyitwillberepaired;ausabilityQAannotationmightdescribehoweasyitistolearnthisfunction.?LenBass,PaulClements,RickKazman,distributedunderCreativeCommonsAttributionLicenseQualityAttributeConsiderationsTherearethreeproblemswithpreviousdiscussionsofqualityattributes:Thedefinitionsprovidedforanattributearenottestable.Itismeaninglesstosaythatasystemwillbe“modifiable”.Endlesstimeiswastedonarguingoverwhichqualityaconcernbelongsto.Isasystemfailureduetoadenialofserviceattackanaspectofavailability,performance,security,orusability?Eachattributecommunityhasdevelopeditsownvocabulary.?LenBass,PaulClements,RickKazman,distributedunderCreativeCommonsAttributionLicenseQualityAttributeConsiderationsAsolutiontothefirsttwooftheseproblems(untestabledefinitionsandoverlappingconcerns)istousequalityattributescenariosasameansofcharacterizingqualityattributes.Asolutiontothethirdproblemistoprovideadiscussionofeachattribute—concentratingonitsunderlyingconcerns—toillustratetheconceptsthatarefundamentaltothatattributecommunity.?LenBass,PaulClements,RickKazman,distributedunderCreativeCommonsAttributionLicenseSpecifyingQualityAttributeRequirementsWeuseacommonformtospecifyallqualityattributerequirementsasscenarios.Ourrepresentationofqualityattributescenarioshastheseparts:StimulusStimulussourceResponseResponsemeasureEnvironmentArtifact?LenBass,PaulClements,RickKazman,distributedunderCreativeCommonsAttributionLicenseSpecifyingQualityAttributeRequirementsSourceofstimulus.?Thisissomeentity(ahuman,acomputersystem,oranyotheractuator)thatgeneratedthestimulus.Stimulus.?Thestimulusisaconditionthatrequiresaresponsewhenitarrivesatasystem.Environment.?Thestimulusoccursundercertainconditions.Thesystemmaybeinanoverloadconditionorinnormaloperation,orsomeotherrelevantstate.Formanysystems,“normal”operationcanrefertooneofanumberofmodes.Artifact.?Someartifactisstimulated.Thismaybeacollectionofsystems,thewholesystem,orsomepieceorpiecesofit.Response.?Theresponseistheactivityundertakenastheresultofthearrivalofthestimulus.Responsemeasure.?Whentheresponseoccurs,itshouldbemeasurableinsomefashionsothattherequirementcanbetested.?LenBass,PaulClements,RickKazman,distributedunderCreativeCommonsAttributionLicenseSpecifyingQualityAttributeRequirementsWedistinguishgeneralqualityattributescenarios(“generalscenarios”)—thosethataresystemindependentandcan,potentially,pertaintoanysystem—fromconcretequalityattributescenarios(concretescenarios)—thosethatarespecifictotheparticularsystemunderconsideration.?LenBass,PaulClements,RickKazman,distributedunderCreativeCommonsAttributionLicenseSpecifyingQualityAttributeRequirementsExamplegeneralscenarioforavailability:?LenBass,PaulClements,RickKazman,distributedunderCreativeCommonsAttributionLicenseAchievingQualityAttributesThroughTacticsThereareacollectionofprimitivedesigntechniquesthatanarchitectcanusetoachieveaqualityattributeresponse.Wecallthesearchitecturaldesignprimitivestactics.Tactics,likedesignpatterns,aretechniquesthatarchitectshavebeenusingforyears.Wedonotinventtactics,wesimplycapturewhatarchitectsdoinpractice.?LenBass,PaulClements,RickKazman,distributedunderCreativeCommonsAttributionLicenseAchievingQualityAttributesThroughTacticsWhydowedothis?Therearethreereasons:Designpatternsarecomplex;theyareabundleofdesigndecisions.Butpatternsareoftendifficulttoapplyasis;architectsneedtomodifyandadaptthem.Byunderstandingtactics,anarchitectcanassesstheoptionsforaugmentinganexistingpatterntoachieveaqualityattributegoal.Ifnopatternexiststorealizethearchitect’sdesigngoal,tacticsallowthearchitecttoconstructadesignfragmentfrom“firstprinciples”.Bycataloguingtactics,wemakedesignmoresystematic.Youfrequentlywillhaveachoiceofmultipletacticstoimproveaparticularqualityattribute.Thechoiceofwhichtactictousedependsonfactorssuchastradeoffsamongotherqualityattributesandthecosttoimplement.?LenBass,PaulClements,RickKazman,distributedunderCreativeCommonsAttributionLicenseGuidingQualityDesignDecisionsArchitecturedesignisasystematicapproachtomakingdesigndecisions.Wecategorizethedesigndecisionsthatanarchitectneedstomakeasfollows:AllocationofresponsibilitiesCoordinationmodelDatamodelManagementofresourcesMappingamongarchitecturalelementsBindingtimedecisionsChoiceoftechnology?LenBass,PaulClements,RickKazman,distributedunderCreativeCommonsAttributionLicenseAllocationofResponsibilitiesDecisionsinvolvingallocationofresponsibilitiesinclude:identifyingtheimportantresponsibilitiesincludingbasicsystemfunctions,architecturalinfrastructure,andsatisfactionofqualityattributes.determininghowtheseresponsibilitiesareallocatedtonon-runtimeandruntimeelements(namely,modules,components,andconnectors).?LenBass,PaulClements,RickKazman,distributedunderCreativeCommonsAttributionLicenseCo張or孩di舍na筋ti閥on葛M熄od頃elDe降ci乘si遷on殺s撫ab樓ou汪t御th席e率co昨or充di上na環(huán)ti酸on圾m喪od召elin胸cl欄ud際e:id談en節(jié)ti動(dòng)fy慘t蔽he嘗e村le憑me愈nt沸s宿of陰t折he寇s畫ys延te棕m終th項(xiàng)at陪m聾us疼t便co以or磚di是na檢te超,停or勉a須re依p頭ro羨hi順bi甜te勸d哲fr蓮om鐮c凈oo叫rd澤in次at豆in喇gde牙te島rm搞in堂in照g尼t(yī)h搬e判pr棗op系er會(huì)ti寄es橡o帽f估th更e般co豆or指di冰na玩ti陜on炮,透su開ch圾a殖s貼ti匆me管li敏ne蒼ss賣,并cu陽rr斤en糊cy稿,茅co坑mp細(xì)le心te透ne閃ss柴,拍co紙rr賓ec錦tn趁es悄s,源a擱nd蛋c扛on圓si淹st吳en捷cych子oo慕si覺ng膚t擁he垃c教om肥mu鈴ni鋸ca巖ti雅on免m龍ec遮ha然ni系sm焦sth昨atre濕al切iz碰e愿th桂os體e待pr坑op遮er手ti生es排.笑I變mp質(zhì)or晝ta申nt許p患ro奏pe貝rt妄ie概s襪of劣t絹he吳c領(lǐng)om鉛mu既ni唐ca訊ti遵on翅m柏ec雕ha軍ni錘sm速s釋in茄cl堡ud集e蠅st閥at攀ef特ul瘦v處s.脊s賢ta剝te螞le麗ss央,浩sy殺nc觀hr董on譽(yù)ou已s欺vs乘.膚as劑yn膨ch梨ro廳no竭us放,呼gu陰ar恩an毀te蘭ed扮v幟s.漏n早on嶼-g甘ua勁ra脆nt薪ee收d懂de胸li湊ve食ry賭,稍an繁d頭pe堆rf鍋or架ma進(jìn)nc貫e-逆re語la這te橋d霸pr爽op床er遷ti甘es原s匠uc礙h宏as芹t巴hr膠ou游gh略pu吸t疲an宇d姑la到te澡nc疤y?翼Le給n乖Ba眨ss猶,襯Pa瘋ul驕C盜le雁me耐nt旗s,喉R犯ic竊k四Ka棵zm罪an段,煉di修st崗ri追bu顧te外d綿un派de洲r(nóng)副Cr援ea萍ti渴ve倍C樂om暑mo剩ns猜A警tt蹤蝶ri娃bu備ti習(xí)on襖L優(yōu)ic暢en瓶seDa花ta執(zhí)M命od紫elDe較ci桿si候on略s雅ab足ou凝t鄭th危e眨da角ta臉m擁od場elin遍cl瞧ud道e:ch駝oo支si蛙ng軋t植he亮m柔aj愉or含d倆at辨a恐ab把st賽ra糕ct昨io襲ns側(cè),遣th思ei邪r草op炕er皇at傘io皮ns資,凱an青d爛th狠ei蓮r滑pr召op罷er享ti意es桶.對Th茄is沙i因nc耗lu乘de站s塘de澇te樹rm潑in熟in湊g來ho狂w源th插e(cuò)懶da射ta尾i塞te諒ms暗a迅re送c旋re戴at鬧ed粗,遼in構(gòu)it索ia耽li才ze但d,祝a尋cc翼es簽se雅d,鵲p驢er研si閉st橡ed斬,喇ma條ni純pu辣la賣te臭d,揪t柴ra悲ns擠la相te仔d,倦a魯nd爹d時(shí)es糾tr宣oy圾ed禽.me匠ta莫da脈ta破n紗ee尚de炭d勤fo襯r果co急ns劃is繳te警nt朗i招nt證er絕pr震et心at桶io曉n種of運(yùn)t途he她d亭at輔aor棋ga萄ni讀za美ti幟on險(xiǎn)o險(xiǎn)f乞th黃e泛da婚ta嗽.推Th昏is巧i剪nc蝕lu釀de筒s尺de摟te師rm咱in墾in慣g侍wh目et縫he荒r毀th望e捕da洪ta貫i辭s滴go設(shè)in標(biāo)g舞to但b唇e痕ke霧pt盲i挑n舌a匆re絲式la柏ti雅on損al舍d回at鳳a幻玉ba涼se擾,糾a揪co鞭ll冒ec旁ti賀on喉o說f論ob飾je嗚ct須s耳or晝b孔o(hù)t警h?間Le挨n窄Ba罵ss嫂,糊Pa虎ul竭C越le至me擇nt奧s,正R華ic殺k廉Ka傷zm板an沉,向di右st界ri萌bu赤te撕d女un炮de昏r暑Cr泥ea概ti富ve信C綢om耽mo途ns鹽A供tt穗ri威bu嚼ti米o(hù)n浙L悔ic瓶en小seMa煉na唉ge似me爸nt圣o然f立Re慢so晴ur辨ce鼓sDe兼ci波si我on悅s章fo瘋r晚ma狗na想ge稍me繭nt沙o輝f辭re員so呈ur獄ce蠅sin要cl您ud續(xù)e:id脾en貸ti虜fy譜in傳g送th蘇e克re亮so涼ur板ce妻s桑th植at漠m類us艷t嚷be益m激an葉ag脾ed序a版nd聯(lián)d按et杠er帶mi醋ni性ng奏t匆he明l鳴im唐it謝s餓fo襯r喚ea焦chde引te躲rm員in破in唐g頌wh浮ic別h廉sy養(yǎng)st茶em折e貞le脆me鳴nt掩(s弊)支ma逮na身ge肌e懶ac往h明re妄so詳ur搜cede坊te攜rm巷in許in變g宏ho縱w望re有so螞ur勺ce漏s陣ar養(yǎng)e苦sh不ar迎ed咳a滅nd認(rèn)t短he糖a影rb輩it席ra赤ti陽on作s察tr兄at東eg慌ie登s現(xiàn)em棄pl捏oy逼ed瞇w寫he義n臂th逢er雞e槍is爐c哪on仙te怨nt院io脈nde號te壩rm質(zhì)in揭in承g(shù)頑th冷e肝im炒pa勾ct泥o奔f嶺sa透tu愿ra揭ti帥on殺o羽n叨di訊ff誕er革en師t場re雨so怪ur探ce傳s.?剖Le匠n壤Ba終ss好,身Pa涉ul淘C渣le跳me腳nt菊s,吵R誼ic埋k貍Ka總zm碌an堤,能di萍st擠ri照bu壟te觀d虧un掘de俊r逼Cr監(jiān)ea戒ti拆ve蛙C淡om寫mo獸ns饒A似tt條ri斧bu咐ti籠on罵L似ic雨en也seMa學(xué)pp駕in販g鈔Am窯on值g瓣Ar曬ch拴it杏ec誤tu粉ra今l加El遣em寒en揉tsUs預(yù)ef熄ul抓m傻ap稿pi管ng刮sin選cl聲ud貿(mào)e:th膨e泊ma升pp覺in繪g浩of率m還od材ul劑es晃a嫩nd細(xì)r復(fù)un賺ti殃me卷e棄le炸me掌nt寬s后to鉗e疼ac灘h音ot拔he是r—粱th欄at音i譜s,廟t橫he暑r敵un設(shè)ti棵me染e績le慘me霜nt辛s遮th籃at仇a勺re母c薪re租at頌ed飛f爆ro籮m胸ea筐ch蛙m閘od席ul什e;松t含he枝m搜od歇ul涌es墾t雖ha戚t武co島nt債ai淘n趁th仍e陪co矮de陵f賓or獻(xiàn)e獄ac她h俗ru牢nt普im待e撐el背em擁en激tth怪e銹as籮si麻gn瞎me鈴nt由o掏f甩ru言nt批im渴e私el經(jīng)em俘en肌ts悅t額o誕pr端oc廚es跡so擠rsth擴(kuò)e感as動(dòng)si戶gn糧me幟nt舍o臺f化it犬em今s軟in案t腔he蝦d上at裁a蔽mo謀de格l籍to音d雖at讀a神st音or眠esth貨e綿ma婚pp涉in乖g帽of各m害od于ul保es鉛a啟nd轟r證un版ti徑me蕩e邊le盞me城nt涉s守to耽u朵ni環(huán)ts約o朝f厚de艙li醬ve悉ry?艱Le分n寄Ba遮ss絨,滅Pa欄ul服C誕le擺me戶nt茂s,查R田ic狼k降Ka寨zm恐an否,賓di圍st辦ri允bu奏te搬d姨un暗de叨r棗Cr婦ea芬ti惕ve鏟C懲om萍mo汁ns判A慚tt隨ri學(xué)bu呢ti般on垮L英ic過en伸seBi足nd菠in蓄g光Ti滔meTh付e刮de賊ci巧si性on亦s瘋in撲t錢he責(zé)o化th鬧erca稍te純go速ri禮esha它ve嫂a協(xié)n非as村so濁ci類at殿ed附b謠in舊di嫁ng蜜t桐im燦e淘de牲c(diǎn)i姨si芹on撥.拳Ex晴am口pl故es證o我f漸su堵ch棚b盼in肢di播ng艇t奮im閘e豆de猜ci卻si爹on詢sin適cl運(yùn)ud塔e:Fo飽ral漏lo跨ca齡ti毅on饅o享f概re無sp尾on痕si黎bi院li盡ti竹es蘆y儉ou遵c酸an抽h帳av令e燙bu僻il外d-畝ti壯me慨s蓋el積ec覺ti繪on懶o那f息mo悼du子le厘s養(yǎng)vi畝a偵a咱pa去ra斥me坦te遠(yuǎn)ri冊ze掛dbu蘇il竟d酬sc身ri槽pt邁.Fo確r蟲ch番oi精ce記o軟f犧co掃or亞di怕na乖ti李on鬼m害od拴el鑒y靜ou徐c靈an摘d棄es雨ig小n煌ru滲n-滋ti帽me垃n鬼eg項(xiàng)ot銹ia培ti歸on本o撓f逐pr斤ot坡oc遍ol雄s.Fo辭r么re章so凍ur蹦ce藥m動(dòng)an邪ag捎em郵en營t布yo中u軍ca跑n蘋de莖si萬gn抓a揀s毀ys劣te會(huì)m泊to形a蠻cc籮ep膽t賺ne婦w膝pe車ri坐ph偶er偷al諒d話ev傳ic蒼es府p患lu擠gg技ed低i步n餃at核r王un值-ti鐘me井.Fo假r坊ch撇oi微ce娘o壺f娛te香ch勁no釋lo儀gy犁y槽ou胞c扶an用b鍛ui逐ld擦a慰n典ap炊p-薄st慈or轎e提fo喇r干a兆sm矮ar算t患ph貞on嗚e迫th么at穩(wěn)a們ut漠om西at桌ic引al決ly階d盼ow號nl鄰oa嗽ds線t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