外文翻译UML 20 序列图组合碎片.docx

外文翻译UML 20 序列图组合碎片.docx

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外文翻译UML20序列图组合碎片

中文2270字

UML2.0SequenceDiagramCombinedfragments

Thediagram'spurpose

Thesequencediagramisusedprimarilytoshowtheinteractionsbetweenobjectsinthesequentialorderthatthoseinteractionsoccur.Muchliketheclassdiagram,developerstypicallythinksequencediagramsweremeantexclusivelyforthem.However,anorganization'sbusinessstaffcanfindsequencediagramsusefultocommunicatehowthebusinesscurrentlyworksbyshowinghowvariousbusinessobjectsinteract.Besidesdocumentinganorganization'scurrentaffairs,abusiness-levelsequencediagramcanbeusedasarequirementsdocumenttocommunicaterequirementsforafuturesystemimplementation.Duringtherequirementsphaseofaproject,analystscantakeusecasestothenextlevelbyprovidingamoreformallevelofrefinement.Whenthatoccurs,usecasesareoftenrefinedintooneormoresequencediagrams.

Anorganization'stechnicalstaffcanfindsequencediagramsusefulindocumentinghowafuturesystemshouldbehave.Duringthedesignphase,architectsanddeveloperscanusethediagramtoforceoutthesystem'sobjectinteractions,thusfleshingoutoverallsystemdesign.

Oneoftheprimaryusesofsequencediagramsisinthetransitionfromrequirementsexpressedasusecasestothenextandmoreformallevelofrefinement.Usecasesareoftenrefinedintooneormoresequencediagrams.Inadditiontotheiruseindesigningnewsystems,sequencediagramscanbeusedtodocumenthowobjectsinanexisting（callit"legacy"）systemcurrentlyinteract.Thisdocumentationisveryusefulwhentransitioningasystemtoanotherpersonororganization.

Thenotation

SincethisisthefirstarticleinmyUMLdiagramseriesthatisbasedonUML2,weneedtofirstdiscussanadditiontothenotationinUML2diagrams,namelyanotationelementcalledaframe.TheframeelementisusedasabasisformanyotherdiagramelementsinUML2,butthefirstplacemostpeoplewillencounteraframeelementisasthegraphicalboundaryofadiagram.Aframeelementprovidesaconsistentplaceforadiagram'slabel,whileprovidingagraphicalboundaryforthediagram.TheframeelementisoptionalinUMLdiagrams;asyoucanseeinFigures1and2,thediagram'slabelisplacedinthetopleftcornerinwhatI'llcalltheframe's"namebox,"asortofdog-earedrectangle,andtheactualUMLdiagramisdefinedwithinthebodyofthelargerenclosingrectangle.

Inmostsequencediagrams,however,theUML1.x"in-line"guardisnotsufficienttohandlethelogicrequiredforasequencebeingmodeled.ThislackoffunctionalitywasaprobleminUML1.x.UML2hasaddressedthisproblembyremovingthe"in-line"guardandaddinganotationelementcalledaCombinedFragment.Acombinedfragmentisusedtogroupsetsofmessagestogethertoshowconditionalflowinasequencediagram.TheUML2specificationidentifies11interactiontypesforcombinedfragments.

Alternatives

Alternativesareusedtodesignateamutuallyexclusivechoicebetweentwoormoremessagesequences.3Alternativesallowthemodelingoftheclassic"ifthenelse"logic（e.g.,ifIbuythreeitems,thenIget20%offmypurchase;elseIget10%offmypurchase）.

AsyouwillnoticeinFigure8,analternativecombinationfragmentelementisdrawnusingaframe.Theword"alt"isplacedinsidetheframe'snamebox.ThelargerrectangleisthendividedintowhatUML2callsoperands.4Operandsareseparatedbyadashedline.Eachoperandisgivenaguardtotestagainst,andthisguardisplacedtowardsthetopleftsectionoftheoperandontopofalifeline.5Ifanoperand'sguardequatesto"true,"thenthatoperandistheoperandtofollow.

Figure8:

Asequencediagramfragmentthatcontainsanalternativecombinationfragment

Asanexampletoshowhowanalternativecombinationfragmentisread,Figure8showsthesequencestartingatthetop,withthebankobjectgettingthecheck'samountandtheaccount'sbalance.Atthispointinthesequencethealternativecombinationfragmenttakesover.Becauseoftheguard"[balance>=amount],"iftheaccount'sbalanceisgreaterthanorequaltotheamount,thenthesequencecontinueswiththebankobjectsendingtheaddDebitTransactionandstorePhotoOfCheckmessagestotheaccountobject.However,ifthebalanceisnotgreaterthanorequaltotheamount,thenthesequenceproceedswiththebankobjectsendingtheaddInsuffientFundFeeandnoteReturnedCheckmessagetotheaccountobjectandthereturnCheckmessagetoitself.Thesecondsequenceiscalledwhenthebalanceisnotgreaterthanorequaltotheamountbecauseofthe"[else]"guard.Inalternativecombinationfragments,the"[else]"guardisnotrequired;andifanoperanddoesnothaveanexplicitguardonit,thenthe"[else]"guardistobeassumed.

Alternativecombinationfragmentsarenotlimitedtosimple"ifthenels