软件体系结构英文版aaaa文档格式.docx

软件体系结构英文版aaaa文档格式.docx

《软件体系结构英文版aaaa文档格式.docx》由会员分享，可在线阅读，更多相关《软件体系结构英文版aaaa文档格式.docx（78页珍藏版）》请在冰豆网上搜索。

?

--CityGent#1（MichaelPalin）,TheArchitectsSketch[111]

AspredictedbyPerryandWolf[105],softwarearchitecturehasbeenafocalpointforsoftwareengineeringresearchinthe1990s.Thecomplexityofmodernsoftwaresystemshavenecessitatedagreateremphasisoncomponentizedsystems,wheretheimplementationispartitionedintoindependentcomponentsthatcommunicatetoperformadesiredtask.Softwarearchitectureresearchinvestigatesmethodsfordetermininghowbesttopartitionasystem,howcomponentsidentifyandcommunicatewitheachother,howinformationiscommunicated,howelementsofasystemcanevolveindependently,andhowalloftheabovecanbedescribedusingformalandinformalnotations.

Agoodarchitectureisnotcreatedinavacuum.Alldesigndecisionsatthearchitecturallevelshouldbemadewithinthecontextofthefunctional,behavioral,andsocialrequirementsofthesystembeingdesigned,whichisaprinciplethatappliesequallytobothsoftwarearchitectureandthetraditionalfieldofbuildingarchitecture.Theguidelinethat"

formfollowsfunction"

comesfromhundredsofyearsofexperiencewithfailedbuildingprojects,butisoftenignoredbysoftwarepractitioners.ThefunnybitwithintheMontyPythonsketch,citedabove,istheabsurdnotionthatanarchitect,whenfacedwiththegoalofdesigninganurbanblockofflats（apartments）,wouldpresentabuildingdesignwithallthecomponentsofamodernslaughterhouse.Itmightverywellbethebestslaughterhousedesigneverconceived,butthatwouldbeoflittlecomforttotheprospectivetenantsastheyarewhiskedalonghallwayscontainingrotatingknives.

ThehyperboleofTheArchitectsSketchmayseemridiculous,butconsiderhowoftenweseesoftwareprojectsbeginwithadoptionofthelatestfadinarchitecturaldesign,andonlylaterdiscoverwhetherornotthesystemrequirementscallforsuchanarchitecture.Design-by-buzzwordisacommonoccurrence.Atleastsomeofthisbehaviorwithinthesoftwareindustryisduetoalackofunderstandingofwhyagivensetofarchitecturalconstraintsisuseful.Inotherwords,thereasoningbehindgoodsoftwarearchitecturesisnotapparenttodesignerswhenthosearchitecturesareselectedforreuse.

Thisdissertationexploresajunctiononthefrontiersoftworesearchdisciplinesincomputerscience:

softwareandnetworking.Softwareresearchhaslongbeenconcernedwiththecategorizationofsoftwaredesignsandthedevelopmentofdesignmethodologies,buthasrarelybeenabletoobjectivelyevaluatetheimpactofvariousdesignchoicesonsystembehavior.Networkingresearch,incontrast,isfocusedonthedetailsofgenericcommunicationbehaviorbetweensystemsandimprovingtheperformanceofparticularcommunicationtechniques,oftenignoringthefactthatchangingtheinteractionstyleofanapplicationcanhavemoreimpactonperformancethanthecommunicationprotocolsusedforthatinteraction.Myworkismotivatedbythedesiretounderstandandevaluatethearchitecturaldesignofnetwork-basedapplicationsoftwarethroughprincipleduseofarchitecturalconstraints,therebyobtainingthefunctional,performance,andsocialpropertiesdesiredofanarchitecture.Whengivenaname,acoordinatedsetofarchitecturalconstraintsbecomesanarchitecturalstyle.

Thefirstthreechaptersofthisdissertationdefineaframeworkforunderstandingsoftwarearchitectureviaarchitecturalstyles,revealinghowstylescanbeusedtoguidethearchitecturaldesignofnetwork-basedapplicationsoftware.Commonarchitecturalstylesaresurveyedandclassifiedaccordingtothearchitecturalpropertiestheyinducewhenappliedtoanarchitecturefornetwork-basedhypermedia.ThisclassificationisusedtoidentifyasetofarchitecturalconstraintsthatcouldbeusedtoimprovethearchitectureoftheearlyWorldWideWeb.

ArchitectingtheWebrequiresanunderstandingofitsrequirements,asweshalldiscussinChapter4.TheWebisintendedtobeanInternet-scaledistributedhypermediasystem,whichmeansconsiderablymorethanjustgeographicaldispersion.TheInternetisaboutinterconnectinginformationnetworksacrossorganizationalboundaries.Suppliersofinformationservicesmustbeabletocopewiththedemandsofanarchicscalabilityandtheindependentdeploymentofsoftwarecomponents.Distributedhypermediaprovidesauniformmeansofaccessingservicesthroughtheembeddingofactioncontrolswithinthepresentationofinformationretrievedfromremotesites.AnarchitecturefortheWebmustthereforebedesignedwiththecontextofcommunicatinglarge-graindataobjectsacrosshigh-latencynetworksandmultipletrustboundaries.

Chapter5introducesandelaboratestheRepresentationalStateTransfer（REST）architecturalstylefordistributedhypermediasystems.RESTprovidesasetofarchitecturalconstraintsthat,whenappliedasawhole,emphasizesscalabilityofcomponentinteractions,generalityofinterfaces,independentdeploymentofcomponents,andintermediarycomponentstoreduceinteractionlatency,enforcesecurity,andencapsulatelegacysystems.IdescribethesoftwareengineeringprinciplesguidingRESTandtheinteractionconstraintschosentoretainthoseprinciples,contrastingthemtotheconstraintsofotherarchitecturalstyles.

Overthepastsixyears,theRESTarchitecturalstylehasbeenusedtoguidethedesignanddevelopmentofthearchitectureforthemodernWeb,aspresentedinChapter6.ThisworkwasdoneinconjunctionwithmyauthoringoftheInternetstandardsfortheHypertextTransferProtocol（HTTP）andUniformResourceIdentifiers（URI）,thetwospecificationsthatdefinethegenericinterfaceusedbyallcomponentinteractionsontheWeb.

Likemostreal-worldsystems,notallcomponentsofthedeployedWebarchitectureobeyeveryconstraintpresentinitsarchitecturaldesign.RESThasbeenusedbothasameanstodefinearchitecturalimprovementsandtoidentifyarchitecturalmismatches.Mismatchesoccurwhen,duetoignoranceoroversight,asoftwareimplementationisdeployedthatviolatesthearchitecturalconstraints.Whilemismatchescannotbeavoidedingeneral,itispossibletoidentifythembeforetheybecomestandardized.SeveralmismatcheswithinthemodernWebarchitecturearesummarizedinChapter6,alongwithanalysesofwhytheyaroseandhowtheydeviatefromREST.

Insummary,thisdissertationmakesthefollowingcontributionstosoftwareresearchwithinthefieldofInformationandComputerScience:

∙aframeworkforunderstandingsoftwarearchitecturethrougharchitecturalstyles,includingaconsistentsetofterminologyfordescribingsoftwarearchitecture;

∙aclassificationofarchitecturalstylesfornetwork-basedapplicationsoftwarebythearchitecturalpropertiestheywouldinducewhenappliedtothearchitectureforadistributedhypermediasystem;

∙REST,anovelarchitecturalstylefordistributedhypermediasystems;

and,

∙applicationandevaluationoftheRESTarchitecturalstyleinthedesignanddeploymentofthearchitectureforthemodernWorldWideWeb.

CHAPTER1

SoftwareArchitecture

Inspiteoftheinterestinsoftwarearchitectureasafieldofresearch,thereislittleagreementamongresearchersastowhatexactlyshouldbeincludedinthedefinitionofarchitecture.Inmanycases,thishasledtoimportantaspectsofarchitecturaldesignbeingoverlookedbypastresearch.Thischapterdefinesaself-consistentterminologyforsoftwarearchitecturebasedonanexaminationofexistingdefinitionswithintheliteratureandmyowninsightwithrespecttonetwork-basedapplicationarchitectures.Eachdefinition,highlightedwithinaboxforeaseofreference,isfollowedbyadiscussionofhowitisderivedfrom,orcomparesto,relatedresearch.

1.1Run-timeAbstraction

A 

softwarearchitecture 

isanabstractionoftherun-timeelementsofasoftwaresystemduringsomephaseofitsoperation.Asystemmaybecomposedofmanylevelsofabstractionandmanyphasesofoperation,eachwithitsownsoftwarearchitecture.

Attheheartofsoftwarearchitectureistheprincipleofabstraction:

hidingsomeofthedetailsofasystemthroughencapsulationinordertobetteridentifyandsustainitsproperties[117].Acomplexsystemwillcontainmanylevelsofabstraction,eachwithitsownarchitecture.Anarchitecturerepresentsanabstractionofsystembehavioratthatlevel,suchthatarchitecturalelementsaredelineatedbytheabstractinterfacestheyprovidetootherelementsatthatlevel[9].Withineachelementmaybefoundanotherarchitecture,definingthesystemofsub-elementsthatimplementthebehaviorrepresentedbytheparentelement'

sabstractinterface.Thisrecursionofarchitecturescontinuesdowntothemostbasicsystemelements:

thosethatcannotbedecomposedintolessabstractelements.

Inadditiontolevelsofarchitecture,asoftwaresystemwilloftenhavemultipleoperationalphases,suchasstart-up,initialization,normalprocessing,re-initialization,andshutdown.Eachoperationalphasehasitsownarchitecture.Forexample,aconfigurationfilewillbetreatedasadataelementduringthestart-upphase,butwon'

tbeconsideredanarchitecturalelementduringnormalprocessing,sinceatthatpointtheinformationitcontainedwillhavealreadybeendistributedthroughoutthesystem.Itmay,infact,havedefinedthenormalprocessingarchitecture.Anoveralldescriptionofasystemarchitecturemustbecapableofdescribingnotonlytheoperationalbehaviorofthesystem'

sarchitectureduringeachphase,butalsothearchitectureoftransitionsbetweenphases.

PerryandWolf[105]defineprocessingelementsas"

transformersofdata,"

whileShawetal.[11