Chapter 4A Technique for Architecture and Design文档格式.docx

Chapter 4A Technique for Architecture and Design文档格式.docx

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∙Inputs,Outputs,andDesignSteps

∙IdentifyArchitectureObjectives

∙KeyScenarios

∙ApplicationOverview

∙KeyIssues

∙CandidateSolutions

∙WhattoDoNext

∙ReviewingYourArchitecture

∙RepresentingandCommunicatingYourArchitectureDesign

Overview

Thischapterdescribesaniterativetechniquethatyoucanusetothinkaboutandsketchoutyourpotentialarchitecture.Itwillhelpyoutobringtogetherthekeydecisionsdiscussedinthisguide;

includingqualityattributes,architecturestyles,applicationtypes,technologies,anddeploymentdecisions.

Thetechniqueincludesaseriesoffivemainsteps,eachofwhichbreaksdownintoindividualconsiderationsexplainedthroughouttheremainderoftheguide.Theiterativeprocesswillhelpyoutoproducecandidatesolutionsthatyoucanfurtherrefinebyrepeatingthesteps,finallycreatinganarchitecturedesignthatbestfitsyourapplication.Attheendoftheprocess,youcanreviewandcommunicateyourarchitecturetoallinterestedparties.

Dependingonyourorganization'

sapproachtosoftwaredevelopment,youmayrevisityourarchitecturemanytimesduringthelifetimeofaproject.Youcanusethistechniquetorefineyourarchitecturefurther,buildingonwhatyouhavelearnedintheinterveningperiodofspiking,prototyping,andactualdevelopment.

Itisalsoimportanttorealizethatthisisjustonepossibleapproach.Therearemanyothermoreformalapproachestodefining,reviewing,andcommunicatingyourarchitecture.Somearediscussedbrieflyattheendofthischapter.

Inputs,Outputs,andDesignSteps

Theinputstoyourdesigncanhelpyoutoformalizetherequirementsandconstraintsthatyourarchitecturemustaccommodate.Commoninputsareusecasesandusagescenarios,functionalrequirements,non-functionalrequirements（includingqualityattributessuchasperformance,security,reliability,andothers）,technologicalrequirements,thetargetdeploymentenvironment,andotherconstraints.

Duringthedesignprocess,youwillcreatealistofthearchitecturallysignificantusecases,thearchitectureissuesthatrequirespecialattention,andthecandidatearchitecturesolutionsthatsatisfytherequirementsandconstraintsdefinedinthedesignprocess.Acommontechniqueforrefiningthedesignovertime,untilitsatisfiesalloftherequirementsandadherestoalloftheconstraints,isaniterativetechniqueconsistingofthefivemajorstagesshowninFigure1.

Figure1 

Theiterativestepsforcorearchitecturedesignactivities

Thesteps,describedinmoredetailinthefollowingsections,are:

1.IdentifyArchitectureObjectives.Clearobjectiveshelpyoutofocusonyourarchitectureandonsolvingtherightproblemsinyourdesign.Preciseobjectiveshelpyoutodeterminewhenyouhavecompletedthecurrentphase,andwhenyouarereadytomovetothenextphase.

2.KeyScenarios.Usekeyscenariostofocusyourdesignonwhatmattersmost,andtoevaluateyourcandidatearchitectureswhentheyareready.

3.ApplicationOverview.Identifyyourapplicationtype,deploymentarchitecture,architecturestyles,andtechnologiesinordertoconnectyourdesigntotherealworldinwhichtheapplicationwilloperate.

4.KeyIssues.Identifykeyissuesbasedonqualityattributesandcrosscuttingconcerns.Thesearetheareaswheremistakesaremostoftenmadewhendesigninganapplication.

5.CandidateSolutions.Createanarchitecturespikeorprototypethatevolvesandimprovesthesolutionandevaluateitagainstyourkeyscenarios,issues,anddeploymentconstraintsbeforebeginningthenextiterationofyourarchitecture.

Thisarchitecturalprocessismeanttobeaniterativeandincrementalapproach.Yourfirstcandidatearchitecturewillbeahigh-leveldesignthatyoucantestagainstkeyscenarios,requirements,knownconstraints,qualityattributes,andthearchitectureframe.Asyourefineyourcandidatearchitecture,youwilllearnmoredetailsaboutthedesignandwillbeabletofurtherexpandkeyscenarios,yourapplicationoverview,andyourapproachtoissues.

Youshouldnottrytobuildyourarchitectureinasingleiteration.Eachiterationshouldaddmoredetail.Donotgetlostinthedetails,butinsteadfocusonthemajorstepsandbuildaframeworkonwhichyoucanbaseyourarchitectureanddesign.Thefollowingsectionsprovideguidelinesandinformationoneachofthesteps.

IdentifyArchitectureObjectives

Architectureobjectivesarethegoalsandconstraintsthatshapeyourarchitectureanddesignprocess,scopetheexercise,andhelpyoudeterminewhenyouarefinished.Considerthefollowingkeypointsasyouidentifyyourarchitectureobjectives:

∙Identifyyourarchitecturegoalsatthestart.Theamountoftimeyouspendineachphaseofarchitectureanddesignwilldependonthesegoals.Forexample,areyoubuildingaprototype,testingpotentialpaths,orembarkingonalong-runningarchitecturalprocessforanewapplication?

∙Identifywhowillconsumeyourarchitecture.Determineifyourdesignwillbeusedbyotherarchitects,ormadeavailabletodevelopersandtesters,operationsstaff,andmanagement.Considertheneedsandexperienceofyouraudiencetomakeyourresultingdesignmoreaccessibletothem.

∙Identifyyourconstraints.Understandyourtechnologyoptionsandconstraints,usageconstraints,anddeploymentconstraints.Understandyourconstraintsatthestartsothatyoudonotwastetimeorencountersurpriseslaterinyourapplicationdevelopmentprocess.

ScopeandTime

Basedonthehigh-levelgoalsforyourarchitecture,youcanscopetheamountoftimetospendoneachofyourdesignactivities.Forexample,aprototypemightonlyrequireafewdaystodesign,whileacompleteandfullydetailedarchitectureforacomplexapplicationcouldpotentiallytakemonthstocomplete—andmayinvolvearchitectureanddesignovermanyiterations.Useyourunderstandingoftheobjectivestodeterminehowmuchtimeandenergytospendoneachstep,togainanunderstandingofwhattheoutcomewilllooklike,andtodefineclearlythepurposeandprioritiesofyourarchitecture.Possiblepurposesmightinclude:

∙Creatingacompleteapplicationdesign.

∙Buildingaprototype.

∙Identifyingkeytechnicalrisks.

∙Testingpotentialoptions.

∙Buildingsharedmodelstogainanunderstandingofthesystem.

Eachofthesewillresultinadifferentemphasisondesign,andavaryingtimecommitment.Forexample,ifyouwanttoidentifykeyrisksinyourauthenticationarchitecture,youwillspendmuchofyourtimeandenergyidentifyingauthenticationscenarios,constraintsonyourauthenticationarchitecture,andpossibleauthenticationtechnologychoices.However,ifyouareintheearlystagesofconsideringtheoverallarchitectureforanapplication,authenticationwillbeonlyoneofmanyotherconcernsforwhichyouaddressanddocumentsolutions.

Someexamplesofarchitectureactivitiesarebuildingaprototypetogetfeedbackontheorder-processingUIforaWebapplication,testingdifferentwaystomaplocationdatatosearchresults,buildingacustomerorder-trackingapplication,anddesigningtheauthenticationandauthorizationarchitectureforanapplicationinordertoperformasecurityreview.

KeyScenarios

Inthecontextofarchitectureanddesign,a 

usecase 

isadescriptionofasetofinteractionsbetweenthesystemandoneormoreactors（eitherauseroranothersystem）.A 

scenario 

isabroaderandmoreencompassingdescriptionofauser'

sinteractionwiththesystem,ratherthanapaththroughausecase.Whenthinkingaboutthearchitectureofyoursystem,thegoalshouldbetoidentifyseveralkeyscenariosthatwillhelpyoutomakedecisionsaboutyourarchitecture.Thegoalistoachieveabalancebetweentheuser,business,andsystemgoals（asshowninFigure1ofChapter1"

WhatisSoftwareArchitecture?

"

）.

Keyscenariosarethosethatareconsideredthemostimportantscenariosforthesuccessofyourapplication.Keyscenarioscanbedefinedasanyscenariothatmeetsoneormoreofthefollowingcriteria:

∙Itrepresentsanissue—asignificantunknownareaoranareaofsignificantrisk.

∙Itreferstoanarchitecturallysignificantusecase（describedinthefollowingsection）.

∙Itrepresentstheintersectionofqualityattributeswithfunctionality.

∙Itrepresentsatradeoffbetweenqualityattributes.

Forexample,yourscenarioscoveringuserauthenticationmaybekeyscenariosbecausetheyareanintersectionofaqualityattribute（security）withimportantfunctionality（howauserlogsintoyoursystem）.Anotherexamplewouldbeascenariothatcenteredonanunfamiliarornewtechnology.

ArchitecturallySignificantUseCases

Architecturallysignificantusecaseshaveanimpactonmanyaspectsofyourdesign.Theseusecasesareespeciallyimportantinshapingthesuccessofyourapplication.Theyareimportantfortheacceptanceofthedeployedapplication,andtheymustexerciseenoughofthedesigntobeusefulinevaluatingthearchitecture.Architecturallysignificantusecasesare:

∙BusinessCritical.Theusecasehasahighusagelevelorisparticularlyimportanttousersorotherstakeholderswhencomparedtootherfeatures,oritimplieshighrisk.

∙HighImpact.Theusecaseintersectswithbothfunctionalityandqualityattributes,orrepresentsacrosscuttingconcernthathasanend-to-endimpactacrossthelayerandtiersofyourapplication.AnexamplemightbeaCreate,Read,Update,Delete（CRUD）operationthatissecurity-sensitive.

Afteryouhavedetermine