Model-Driven Evolution of Software Architectures - Software and ...
Model-Driven Evolution of Software Architectures - Software and ...
Model-Driven Evolution of Software Architectures - Software and ...
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7.7. TargetMetamodel 147<br />
tworesourceusagepatternsareexecutedinparallel.<br />
Conditionalexecution Theidiomforconditionalexecutionismorecomplicated.<br />
First,werequireittobespecifiedusingachoicePseudostatewith<br />
twooutgoingTransitions. OnespecifiessomeconditionasaGuard;the<br />
otherspecifies [else]asaGuard.Furthermore,werequire‘proper’nesting<br />
<strong>of</strong>conditionalactivationpathsinastatemachine.Thismeansthatwerequirepairs<strong>of</strong>corresponding,alternativepathsthroughthestatemachinetobemergedoneatatime(usingjunctionPseudostates),<strong>and</strong>inreverseorder.Figure7.7onthefollowingpagecontainsseveral(nested)examples<strong>of</strong><br />
thispattern(choice<strong>and</strong>junctionPseudostatesaredepictedusingdiamonds<br />
<strong>and</strong>thesmallerblackcircles,respectively).<br />
Withoutthisrequirementforpropernesting,findingtheset<strong>of</strong>States,<br />
<strong>and</strong>thusActions,whichareenabledwhensomeGuardevaluatestotrue<br />
wouldbecomerathercomplicated. Forthetransformation<strong>of</strong>oursource<br />
modelstotargetmodels,findingthisset<strong>of</strong>statesisanecessarystep.‘Nonproper’nestingoccurs,forinstance,inthebottom-half<strong>of</strong>theprocesswafer<br />
requestinFigure7.5onpage141. Thisresultsinreplication<strong>of</strong>theactivitiesperformedoneachpathduringnormalisation.ThethreeCompositeStatesinthebottom-half<strong>of</strong>Figure7.7onthefollowingpageillustrate<br />
thisreplication. Part<strong>of</strong>thisparticularnormalisationstepiscoveredby<br />
constraint C4,whichstatesthatapaththroughastatemachinecanonly<br />
splitintwopaths<strong>and</strong>thatnomorethantwopathscanbejoinedinasingle<br />
statenode.BecausetheOCLconstrainttoexpresspropernestingisrather<br />
lengthy,wedidnotincludeithere.<br />
7.7 TargetMetamodel<br />
Weconsider TRSasthegivenparadigmfortheend-point<strong>of</strong>themigration.Thisend-pointisbasedonaresearchprototype[V<strong>and</strong>enNieuwelaar,<br />
2004]. Usingthe TRSparadigm,amanufacturingrequestistranslated<br />
intovalidmachinebehaviourintwophases.First,uponarrival<strong>of</strong>amanufacturingrequest,aschedulingprobleminthecontext<strong>of</strong>thatrequestis<br />
instantiatedduringaplanningphase.Forthis,therequestisinterpreted<br />
throughrulesthatoperateoncapabilities(resourcetypes)<strong>and</strong>behaviours<br />
(tasktypes). Here,amanufacturingactivitycorrespondstoatask<strong>and</strong>a<br />
mechatronicsubsystemtoaresource. Thefirstphaseresultsinahierarchicaldigraphthatconsists<strong>of</strong>tasks<strong>and</strong>their(precedence)relations.Nodes<br />
inthisgraphcanbecompositetoeitherdenoteaset<strong>of</strong>tasksthatallneed<br />
tobeexecutedortodenoteaset<strong>of</strong>tasks<strong>of</strong>whichonlyonewillbeexecutedbasedonsomecondition.Second,aschedulingphaseconstructively<br />
assignstasksinthisdigraphtospecificresourcesovertime[Viennot,1986;
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