Position paper: An integration approach of service composition models: from choreography to orchestration

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Position paper: An integration approach of service composition models: from choreography to orchestration

Sirine Rebai, Hatem Hadj Kacem, Ahmed Hadj Kacem, Nawal Guermouche

To cite this version:

Sirine Rebai, Hatem Hadj Kacem, Ahmed Hadj Kacem, Nawal Guermouche. Position paper: An

integration approach of service composition models: from choreography to orchestration. 2012. �hal-

00733861�

servie omposition models: From horeography

to orhestration

Sirine Rebai

∗

, Hatem Hadj Kaem

†

, Ahmed Hadj Kaem

‡

,

and NawalGuermouhe

§

1

ReDCAD Laboratory,University of Sfax,Tunisia

2

CNRS, LAAS, 7avenue du olonel Rohe, F-31400 Toulouse,

Frane

3

Univ de Toulouse, INSA, LAAS, F-31400Toulouse,Frane

Marh 31,2012

Abstrat

Thispaperintroduesanapproahaddressingthetransition fromhore-

ographytoorhestration. Asfarasvalidationmethodisahievedthrough

theuseofmodel-heker. Weare interestedinvariouslevelsoftransfor-

mations. Infat,transformationsare dierent intheir departurepoints.

Initially,theproessoftransformation,whihwewanttoestablishisbased

onasetofheterogeneousbusinessprotools. Thisunitwill onsequently

provideahoreographyasresult,whihuniesthem.So,toensurethein-

tegrationproessing,wedeneameta-modelforthehoreographymodel.

Atthislevel,ertainveriationswilltakeplae. Throughthem,wewill

hekasetofpropertiesrelatedtothehoreographiesmaintainedafterthe

integration. Then,thishoreography willbetransformedinto anorhes-

tration. Thus, oherene between horeography and orhestrationmust

be hekedwhile showing the relation of onformity between thesetwo

dierentompositionmodels. Theobtained orhestrationmustpreserve

thetotalbehaviorofthesystemasspeiedinhoreographyandsupport

alltheresponsibility,whihisalreadydenedbytheothermodel(hore-

ography). So,to faetheundeidabilityoftheproblem ofsynthesis,the

hoieofthebesttransformationwillbesupportedbythenumberofpre-

servedproperties. Indeed, thispassage is aompaniedby averiation

∗

si.rebaigmail.om

†

hatem.hadjkaemfsegs.rnu.tn

‡

ahmed.hadjkaemfsegs.rnu.tn

§

Nawal.Guermouhelaas.fr

horeographyareonsidredas ommonandothers,whiharerelative to

thosehekedbytheorhestrationarejudged asloal. Towardstheend

ofthisproess,andinordertovalidatethetransformation,wemusthek

themaintainedproperties. Thishekingwillbeillustratedbytheuseof

themodel-heker,whihdependsontheproperties.

1 Introdution

Nowadays, we note that there is a signiant inrease in system omplexity.

Thus, theissueofreusabilityisalwaysamajorhallenge. Infat,softwarear-

hitetures havealways been thebridge betweenstrategy and developmentof

information systems[3℄. Theyare aneetive response to problems faedby

ompaniesin termsofreusability, interoperabilityin additionto reduingou-

pling between the various systems that implement theirinformation systems.

Theservieorientedapproahseekstoimplementthereuseofanexistingservie

[18℄. SOAsarebetterknownunder theirversionofwebservie,that appeared

as anew tehnology oeringa means to exhange data between appliations

[7℄. Indeed,thedevelopmentofappliationsbasedonwebserviesisensuredby

using the omposition tehnique, whih is essentialto theappliations imple-

mentation. It is denedas"the proessof ombiningexistingserviesto form

new servies." Choreography and orhestration are two dierent mehanisms

used in servieomposition. Choreography provides an abstrat speiation

toahieveaommon businessgoal, whileorhestrationprovidesexeutionde-

tailswhih are neededto realizethis goal. Theorhestrationproess ontains

additionalinformationnotfoundin the horeographyspeiation (Privateor

internal ations for eah role, the details in theerror handling, exeution de-

tails...). Although, thehoreographyservesasaontratbetweenthedierent

serviepartners,itannotbeperformedbyitself: itsmodelsarenotexeutable.

Tollthisgap,wehavetotransformhoreographyspeiationtoorhestration

proess,whihisthepratialimplementationofthehoreography. Itbringsthe

ontributionofonepartytotheservieomposition. Infat,thesemehanisms

aredierentintheirnatureandtheyomplementeahother.

Moreover,therearemanyworks,whihareinterestedinthetransformationpro-

ess. Themajorityofthem, basedontheModelDrivenArhitetureonepts,

havestudied thetransformationfrom CDLspeiationstoBPEL proess. In

addition, they have been interestedin verifying some aspets of onformane

relationshipbetweenthehoreographyandtheorhestration. Inthiswork,we

overometheseproblemsbyintroduinganapproah,whihonsistsintheinte-

grationofservieompositionmodelsandweseektovalidateourtransformation

proessthroughtheadequatemodel-heker.

Wehavestruturedthis paperasfollows: InSetion 2, anoverviewofservie

omposition is presented. We give a surveyof related work in Setion 3. In

Setion4,wepresentourapproahfollowedbyasetiondesribingaasestudy.

Thelast setionontainsashortonlusionandtraksforfuture works.

Webserviesareakeytehnologyforsupportingandperformingbusiness pro-

esses[1℄. Theorhestrationandhoreographyaretwoomplementarymeha-

nismsforservieompositionat dierentabstrationlevels.

2.1 Orhestration

An orhestration is a proess viewed only from the perspetive of a business

partner,whih takes theontrol of theproess. It oersa entralized vision.

Also,inthisompsitionmodel,theinvolvedserviesareunderontrolofasingle

endpointentralproess(orhestrator). Thisproessoordinatestheexeution

ofdierentationsontheinvolvedwebservies. These latterdonotknowand

donotneedto knowthatthey areinvolvedin aomposition proess. In fat,

orhestrationdesribesthewayinwhihseparate webserviesanbebrought

togetherinaonsistentmannertoprovideahighervalueservie. Itouldonly

desribeasingleproesswhen multipleproessesinteratwitheah other.

2.2 Choreography

Thehoreographyhas been introdued asa newview onservies interation.

Itis adesriptionof abstrat protools. It oersaollaborativedeentralized

oordination. Choreography,whihisdesriptiveinnature,desribestheinter-

ationontratbetweentwoormorewebservies[12℄. Ithelpsto desribethe

serviesbehaviorin omposition. Fortherest weneedto distinguishbetween

thefollowingtwodenitions:

•

tothepublipartsoftheirloalproessesvisibletootherpartiipants.

•

partners.

Infat,therst denition wasdisussedin thework of[15℄ andit hasbeena

entralelementthroughouthiswork. Astotheseonddenition,itrepresented

thestartingpointofthetransformationproesspresentedinthesamework. All

thesame,Ederbenetted well fromthese twodenitionsthroughout his work

[5℄.

Choreographylanguagesreetthelong-terminterations. Theyallowtheuser

to desribe the peer-to-peer ollaboration between servies by dening their

ommonobservablebehavior. Intherealmofhoreography,twodierentmod-

elingapproahesdier:

Interation models based approah Theelementary interations,namely

demandandtheexhangeofrequest-responsemessages,arethebasielements

of this approah. Behavioral dependenies, shown in these interations and

tothistype,weanlistWS-CDLandLet'sDane:

•

ommonbehaviorforallpartiipantsandmodelsamessagebetweentwo

(ormore)partiipants. Itprovidesmoredetailedmodels.

•

pendent visual notation. The ommuniation ation isperformed byan

ator playing arole. The exhanged messagesare message sending and

messagereeipt ation.

Interonnetion models based approah The ontrol ow is dened by

partiipants. Thebehaviorofeahpartiipantandtheexhangedmessagesare

represented. However,themodelsouldbeinompatible.

•

dent language. It uses a typial notation for every proess. To make

interonnetingdierentproesses,thislanguageusesmessagesows. In

thatway,allinterationsarelistedwiththedenition oftheontrolow

betweenthem. Hene,ommuniationsareestablishedbyusingdata ob-

jetsandommuniatingativities. Nevertheless,BPMNdoesnotsupport

multipleinstanesofpartiipants. So,tosolvethisproblem,itusesaPool

set to representmultiple partiipantsin one onversationand usesPBD

(PartiipantBehaviorDesription) asviewsfromtheindividualpartners.

•

supports all the dierent horeographies design phases. It ensures om-

muniationbetweenpartiipantsbyusingmessagelinks. Thislanguageis

builtonthree artifat:

- PartiipantBehaviorDesription: denestheontrolowdependen-

iesbetweenativitiesofinvolvedpartiipantsinthehoreography;

- Partiipant Topology: denes thepartiipantstype,theirreferenes

andthemessagelink whihbuild thehoreographystruture;

- Partiipant Grounding: it ontains the tehnial onguration and

enablesthereuseofhoreographyspeiation.

Eahofthese languageshasbroughtnewonepts,and redenedones already

knownbyothers. Thisreatedamultitude ofonepts,sometimesoverlapping

andamultitudeofwaystomanipulate. Infat,onepts,denedbyorhestra-

tionand horeographylanguagesare interesting, and provide additionalskills

andknowledgein theworldof web serviesomposition. However,sometimes

theseskillsareappliableinapartiularareaandforspeialneedsthatarenot

alwaysneessaryin otherareas. Infat,anintegrated solutionhasto address

allaspets ofdevelopmentsto failitatethe work ofdierent stakeholdersand

redue development time. Yet, theintegration of servies from heterogeneous

souresisstillamajorhallengefaingthedeveloper.

Inthissetion,webrieymentiontheresearhdevelopmentsthataimtotrans-

form horeographyto orhestration and those interestedin the integration of

serviesompositionmodels.

3.1 Composition of omposition models

In[9℄,theresearhisspeiallyfousedonproessesandonstrutionof pro-

essesbased on software. The authors study the oordinationof appliations

managed by the proess, partiularly orhestration and horeography of web

servieseld. Theyalsoimplementanappliationfororhestrationofwebser-

vies,usingtheplatformMelusinewhihtheydesignedthemselves,toestablish

proessessoftware. Toset this appliation, theywere inspiredby asample in

thelanguagespeiationWSCI.Toillustratetheirontributions,theypresent

anappliation of webserviesorhestration ofonly twoservies. Inaddition,

they dene a proess meta-model ontaining a minimum of onepts used to

buildoordinationproessesthatareunderstandableandeasytohandleforthe

softwaredeveloper. Weseethroughthisexampleofserviesorhestration,they

oeranarhiteturethat providesasolutionto theshortagesof orhestration

andhoreographylanguages(manyspeializedonepts;oneptsoverlap;lose

toprogramminglanguages)thatmaketherealizationofaunifyingmeta-model

utopian. Tobuilda omposition software usingthis approah,it is important

that theonepts representingthe logiof the appliation are separatedfrom

their implementation, and reied at runtime. Thus, it is possibleto use this

approahtobuildawebservieompositionwheneverthesoftwareisbasedon

thethree tieredarhitetureornot.

In[4℄,Clémentinepresentstwotypesoforhestrationomposition. Therstone

istheompositionoftwoorhestrationsthatarealreadytheresultofaservie

omposition. Theseonddealswiththeompositionofanorhestration(there-

sultofasetofserviesomposition)andanelementaryorhestration,whihan

be,sometimes,onsideredasaservie. Theauthorlaimsthat someproblems

may be enountered when arryingout theomposition ofthe orhestrations,

whihmustalwaysbetakeninto aount:

•

•

•

•

expetationsthat anleadtoerrors;

•

athird. Heonsiders it asafusion. Inorder to dene a fusionalgorithm, he

reatesameta-modelomposition,whihinludesalltheonepts. Atrst,he

identiestheidentialelementsinordertounifythemandwill,eventually,all

theuserinasesofonit. Towardstheend,toidentifyonitsandhekthe

ompatibilitypropertiesbetweentheorhestrations,hereliedonformalmethods

thatoeravarietyofsolutionsthatanbevalidated.

In[6℄, theauthorpresentsanewoneptualmodelforwebservieshoreogra-

phies. Throught his work, he onsiders that there is a horeography shared

amongseveral partners. Infat,headmits that"The global horeography ap-

turestheoreofabusinessproess"[5℄. Therefore,eahpartnerisresponsiblefor

therealizationofeahhoreographypart. Toahievethis,heusesthefollowing

denition "The other horeographies desribe parts of the global horeography

in the needed detail for implementation". So, he introdues a new appraoh

alledviewdrivenfederated horeographieswherethelatterarejudgedasfed-

erationsofhoreographiesandorhestrations[17℄. Toahievehispurpose,Eder

assumes that horeographies must be realized by orhestrations of partners.

Infat,thehoreographydenestheommuniationamongorhestrations. Be-

sides,hedenesameta-model,whihregardstherepresentationoforhestration

andhoreographydesribedasworkowsmodel. Inaddition, heonsiders the

inter-layeronformaneasaentralrequirementoftheobtainedmodel(feder-

ated horeographies). However, he is limited only to strutural onformane,

temporalonformane,messagingonformaneanddataowonformane.

3.2 From horeography to orhestration Models

In[20℄, the authors disuss therelationship betweenthe twodierent meha-

nismsfortheservieompositionin theirwork. Theyweretherstwhointro-

duedthe oneptofinformation gapto mentionthe dierentlevelsof details

betweenhoreographyandexeutionbusinessproess. Theypresenttheirtrans-

formationproess in a virtual organization. Although, it is an unidiretional

transformation,itsimplementationdetetserrorsorviolatedonstraints.

Regarding[15℄, thetransformationfromCDLspeiationto BPELproessis

presented. In suh transformation, the horeographyis viewed from two as-

pets, namelyas a global and aloal horeography. Theglobal horeography

orrespondstothemessageexhangefrom aglobalperspetive. Itis alsoon-

sideredasaoordinationprotool.Whileloalhoreographyorrespondstothe

messageexhangefrom asinglepartyperspetive. Theauthors generateloal

horeographyfromglobalones,whihwillbeusedtogenerateanorhestration

proessfor eah part. Duringthetransformationproess, themappingis well

doumentedandexplainedtogenerateaBPELproessforallinvolvedparties.

Although,itisabidiretionaltransformation,theauthorsdonotexpliitlymen-

tiontherelationshipbetweenhoreographyandorhestrationsandtheyignore

sometransformationmappinginformation.

In[10℄,theauthorillustratesthebasiideaofMDA(ModelDrivenArhiteture)

bilityofpartiularly usingthedriven modelstehnologybasedonmeta-model

transformationstorealizethetransformationofhoreographytoasetoforhes-

trations.Thus,thisapproahoersasolution;inludingamethodologythat al-

lows(semi-)automatiallythetransformationproess. Inaddition,throughout

thiswork,hestudies therelationshipbetweenhoreographyand orhestration

atthearhiteturallevelratherthanlanguage. Infat,suh arhiteturalrela-

tionshipbetweenthetwoompositionmodelspromotesatransformation,whih

isindependentofallthespeiationlanguagesforbothhoreographyandor-

hestration. Theyformalizethemappingto avoidambiguousinterpretation.

In [14℄, the authors represent an automated approah of synthesis of orhes-

trator from horeography. Their horeography speied in BPMN/BPEL is

translated to a BPMN/BPEL, whih is, also, at the base of orhestrator. In

theirwork,theyhavehosenBPMN/BPELhoreography,representedinFinite

State Mahine (FSM), as abase for their formal approah of synthesizing an

orhestrator. Theorretnessveriationmethods of theorhestrator,detet-

ingandavoidingdeadloksituationsareinludedinthesynthesizingalgorithm,

whih onstruts the orhestrator. The Petri-net based model is then later

transformedto BPMN/BPEL.

3.3 Synthesis

Bywayofreapitulation,wenotethat manyworkshavefousedonthetrans-

formation from horeography to orhestration. To ahieve their goals, they

essentially foused on the priniples of MDA. Furthermore, they ignored the

other landings of transformation(proessing)and did not tryto verify the re-

lation ofonformitybetween both models. Infat, weobservethat therewas

ignoraneof other levels either the passagefrom "loal" to "global" horeog-

raphy orthe passagefrom orhestrationto Promela. In addition, they aren't

interestedinhekingtheompatibilityofthetwoproessesoftransformation.

Likewise,onerningtheompositionofserviemodelsomposition,webelieve

thatlittleworkhasealtwiththehoreographiesompositionrealm. Indeed,our

researhispartofthatroute. Infat,theworks,whiharemostloselyrelated

toourworkaredesribedin[6℄, [10℄and[14℄. Indeed, wewillbein ontinuity,

onomposition of omposition modelsside, with thework of Eder[6℄ and,on

theotherside, withthosefromKadhka[10℄andMIlvenna[14℄.

However,to ll the gaps and the shortages enountered by the various works

itedabove(no ompatibilityhek,no validationproessing,one transforma-

tion level, not taking into aount the servie soures heterogeneity and the

overlapping onepts ...), we propose an approah, whih is based on trans-

formation proess from horeography to orhestration. The transition from

horeographytoorhestrationisarriedoutsinethehoreographytoolsdonot

diretlymodelthemajorityofativities. Infat,itisanon-exeutable,abstrat

proessthatdenesthemessageexhangeprotoolandneedsdetails,whihwill

beimplementedbytheorhestration,tobeexeuted. Asarststep,weperform

unifyingthem. Atthislevel,wepresentameta-modelofhoreography. Weper-

formthisintegrationphasetoworkindependentlyofmodelinglanguagesandto

treatallserviesfrom heterogeneoussoures. So,weaninlude allthedier-

entoneptsalreadydened bythedierenthoreographylanguages.Also,we

will avoid theonepts overlapandthe redundant alls. This integration will

buildastartingpointforaseondphasetransformationfrom horeographyto

orhestrationto nallyreahthephaseof thetransformationvalidationwhih

anbeillustratedbytheuseofdierentmodel-heker.

Wehavetomentionthatourontributionsarenotlimitedtothis,butwehoose

toundertakeauditsofpropertiesthatwillbemaintainedaftereahrenement.

Hene, this heks if the overall horeography satisfy all the requirements of

arhiteturespeiations.

4 Approah

In this setion, we present, in detail, our transformation and validation ap-

proah. Wewillsanourwork inavertialmannerfromtopto bottom.

4.1 Fromheterogeneousloalhoreographytoglobalhore-

ography

Our work is interested in dierent levels of transformation proess. In fat,

the transformationsdier in theirstarting point. As arst step, the proess

isbasedonaset ofheterogeneousonversationalprotools(asshownin Figure

1(a)). This groupwill provide ahoreography, that uniesthem, asaresult.

Forthis purpose, we will reate a meta-model for horeography, whih allows

us to work independently of modeling languages. At this level, there will be

heks to take plae. Through them, we will hek a set of properties relat-

ing to horeography maintained after integration [16℄ [15℄ [13℄ [19℄. We note

thatthe globalhoreographymayinlude dierentonversationalprotoolsas

well as orhestrations, whih are onsidered by someauthors as ompositions

mehanismsfrom loalviews[6℄.

4.2 From horeography to orhestration

At thislevel,wedistinguish betweentwotypesof transformations,either one-

to-oneorone-to-many. Infat,theorhestrationproessmustbedevelopedin

aordanewith the horeography. In ourresearh work,we aim to realize a

transitionfrom horeographyto orhestration(as shown in Figure 1(b)). The

resulting orhestration should preserve the overall behavior of the system as

speiedinthehoreography. Soitshouldbeinaordanewithitandsupport

theresponsibilitythatisalreadydened. Theorretnessofthetransformation

onsistsin determiningifthebusiness goalofaninitiator atthehoreography

levelis preservedby theorhestration. Duringthis proess oftransformation,

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someproperties shouldbe preserved. Amongthese properties, theloalprop-

ertiesrefertotheorhestrationproperties;whiletheothers,whihareommon

arereferene for thepropertiesveried by the horeographymehanism. Our

workissubdividedinto twoessentialparts. Therstoneisdevotedtopresent