[Programming Languages] Formal Definitions and Theory—Semantics General Terms

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CompositionalFailure-basedSemanticEquivalencesfor

ReoSpecifications

MohammadIzadi

DepartmentofComputerEngineering

sharifUniversityofTechnology

Tehran,Iranizadi@ce.sharif.eduAliMovaghar

DepartmentofComputerEngineering

sharifUniversityofTechnology

Tehran,Iranmovaghar@sharif.edu

ABSTRACT

Reoisacoordinationlanguageformodelingcomponentcon-

nectorsofcomponent-basedcomputingsystems.Weshow

thatthefailure-basedequivalencesNDFDandCFFDare

congruenceswithrespecttocompositionoperatorsofReo.

CategoriesandSubjectDescriptors

D.2.4[SoftwareEngineering]:Software/ProgramVerifi-

cation—Languages;F.4.3[MathematicalLogicandFor-

malLanguages]:FormalLanguages—Verification;D.3.1

[ProgrammingLanguages]:FormalDefinitionsandThe-

ory—Semantics

GeneralTerms

Languages,Semantics,Verification.

Keywords

ReoSpecificationLanguage,ConstraintAutomata,Failure-

basedEquivalences,Coordination,Component-basedSys-

tems,Semantics.

1.EXTENDEDABSTRACT

Theconceptofcomponentbasedsystems,especiallycom-

ponentbasedsoftware,isaphilosophyorwayofthinking

todealwiththecomplexityindesigninglargescalecom-

putingsystems.Oneofthemaingoalsofthisapproachis

tocomposereusablecomponentsbysomegluecodes.The

modelorthewayinwhichthesecomponentsarecomposed

iscalledcoordinationmodel.Sometimestherearesomefor-

malorprogramminglanguageswhichareusedforspecifica-

tionofcoordinationmodels.Suchlanguagesarecalledas

coordinationlanguages.Reo,asoneofthemostrecently

proposedcoordinationlanguages,isachannelbasedexoge-

nouscoordinationlanguageinwhichcomplexcoordinators

arecompositionallybuiltoutofsimplerones[1,2,3].By

usingReospecifications,complexcomponentconnectorscan

Permissiontomakedigitalorhardcopiesofallorpartofthisworkforpersonalorclassroomuseisgrantedwithoutfeeprovidedthatcopiesarenotmadeordistributedforprofitorcommercialadvantageandthatcopiesbearthisnoticeandthefullcitationonthefirstpage.Tocopyotherwise,torepublish,topostonserversortoredistributetolists,requirespriorspecificpermissionand/orafee.SixthInternationalWorkshoponSpecificationandVerificationofComponent-BasedSystems(SAVCBS2007),September3-4,2007,CavtatnearDubrovnik,Croatia.Copyright2007ACMISBN978-1-59593-721-6/07/0009...$5.00.beorganizedinanetworkofchannelsandbuildinacom-

positionalmanner.Reoreliesonaveryliberalandsimple

notionofchannelsandcanmodelanykindofpeer-to-peer

communication.ThechannelsusedinReonetworkscanbe

consideredassimplecommunicatingprocessesandtheonly

requirementsforthemarethatchannelsshouldhavetwo

ends(orI/Ointerfaces),declaredtobesinkorsourceends,

andauser-definedsemantics.Atsourceendsdataitems

enterthechannelbyperformingcorrespondingwriteopera-

tions.Dataitemsarereceivedfromachannelatsinkends

byperformingcorrespondingreadoperations.Reoallows

foranopenendedsetofchanneltypeswithuserdefined

semantics.

Ifwewanttobeabletoreasonaboutpropertiesofspec-

ificationsorverifytheircorrectness,Reo,aswellasany

otherprocessspecificationlanguages,shouldbegivenab-

stractsemantics.Thekeyquestioningivingasemantic

modeltoaspecificationlanguageis:”Whenevercanwesay

thattwospecificationsortwomodelsareequivalent?”Nu-

merousdefinitionsofdifferentequivalence-relationsfortran-

sitionsystembasedmodelshavebeenpresentedintheliter-

ature.Traceequivalence(automata-theoreticequivalence),

weakbisimilaritypresentedbyMilner[9]andfailure-based

equivalences(CSP-likeequivalences)suchastheequivalence

presentedbyHoare[7]areexamplesoftheseequivalences.

Constraintautomaton,asanextensionoffiniteorB¨uchi

automaton,isaformalismproposedtocapturetheoper-

ationalsemanticsofReo[4].Inaconstraintautomaton,

contrarytofiniteautomataandlabeledtransitionsystems,

thelabelofatransitionisnotasimplecharacteroraction

name.Atransitionlabelcontainsasetofnamesanda(con-

straint)proposition.Thesetofnamesindicatesthenames

ofportswhichareparticipantindoingthetransitionand

thepropositionexpressessomeconstraintaboutthedataof

theports.

Inthispresentation,weareinterestedtoinvestigatefailure-

basedequivalencesforconstraintautomataastheabstract

semanticsofReoandtheircongruencywithrespecttocom-

positionoperatorswhichareusefulincomposingReospec-

ifications.Theultimategoalistoprepareanenvironment

forcompositionalmodelcheckingofReospecificationsus-

ingequivalencebasedreductionmethod.Inthismethod,the

modelsofcomponentsandconnectorsofacomponent-based

systemarereducedwithrespecttoanequivalencerelation

beforebuildingthemodelofthecompletesystem[5,6].An

equivalencerelationshouldhavetwopropertiesinorderto

beusefulintheequivalencebasedcompositionalreduction

method:itshouldpreservetheclassofpropertiestobever-

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