A Flexible Model for Web Service Discovery

AflexiblemodelforWebservicediscoveryRub´enLara1,Miguel´AngelCorella2andPabloCastells21Tecnolog´ıa,Informaci´onyFinanzas,Madrid,[e-mail]2UniversidadAut´onomadeMadrid,Spain.fmiguel.corella,[e-mail]misexpectedtocauseanincreaseinthenumberofavailableWebservices.Inthissetting,advancedfacilitiesforthediscoveryofWebservicesthatprovideagivenfunctionalityarerequiredsothatthisincreasedoesnotcreateabottleneckfortheexploitationofservicesinanSOA.Inthispaper,wepresentamodelforthediscoveryofWebserviceswhichreliesonalternativeviewsofWebservicefunctionalcapabilities,allowingfordifferenttrade-offsbetweentheaccuracyofdiscoveryresultsandtheefficiencyofthediscoveryprocess.Uptothreefilteringsteps,withincreasingcomplexity,canbesuccessivelyappliedinordertorefinediscoveryresults.Furthermore,theuseoftaxonomiesoffunctionalcategories,closetotheintuitionofaverageusers,isintroducedbyourmodelwithatwo-foldpurpose:a)supportingtheuserinthedescriptionofgoalsandWebservices,andb)allowingforacoarse-grainedbuthighlyefficientdiscovery.Duetoitsflexibility,themodelproposedisexpectedtocoverawiderangeofusecases.1IntroductionService-OrientedArchitectures(SOAs)arereceivingincreasingattention,astheypromiseanimportantgaininflexibilityandscalabilityofITsystemsandareductionoftheintegrationburden.However,theadoptionoftheSOAparadigmisnotonlyexpectedtobringbenefitsbutalsotoposenewresearchchallenges.OneofthesechallengesistheautomaticlocationofWebservicesthatcanfulfillagivenfunctionalgoal,anditconstitutesthefocusofthispaper.WeconcentrateontheexploitationoftheformaldescriptionofWebservicefunc-tionalcapabilitiesandofcustomergoalsand,buildingonpreviousworks([13,14,16,17]),weproposeaWebservicediscoverymodelwithsomefeaturesthatwebelievecanmakeitusableinawidevarietyofscenarios,namely:a)itallowsfordifferenttrade-offsbetweenaccuracyofresultsandresponsetimes,basedontheapplicationofdifferentfilters,b)itsupportsusersinthedescriptionoftheirgoalsandWebservices,c)itcanprovidemeaningfulresultsinshorttimesifonlythesimplestfilterisapplied,andd)itcanyieldresultsofconsiderableaccuracyifallavailablefiltersaresuccessivelyap-plied.Additionally,aprototypeofaregistryandadiscoverycomponentimplementingthemodeldesignedhasbeenbuiltasaproof-of-conceptofourapproach.Thisproto-typeispresentedinthepaperaswellassomepreliminaryperformanceevaluationandcomplexityresultsbasedonthelogicallanguagesandreasoningtasksemployed.Thepaperisstructuredasfollows:Section2introducesalternativeviewsofWebservicecapabilitiesusedinourmodel.ThepublicationofWebservicesbyprovidersandthedescriptionofgoalsbycustomersarepresentedinSections3and4,respectively.InSection5,theapplicationofregistry-sidefiltersforlocatingWebservicesthatcanresolvethegoalathandisdescribed,andcustomer-sidefiltersarepresentedinSection6.RelevantrelatedworkisdiscussedinSection7.Finally,ourconclusionsandfutureworkaresummarizedinSection8.2WebServiceCapabilitiesWebservicesarecomputationalentitiesaccessibleusingparticularstandardsandpro-tocols,andusabletorequesttheprovisionofsomeservices,beingaserviceunderstoodasaprovisionofvalueinsomedomain[13,22].Forexample,anairlinecanpublishaWebserviceforthebookingofitsflights;thisWebservicecanbeusedtorequestdifferentparticularbookings,eachbookingbeingaservice.Theprovisionofaserviceresultsontheprovisionofsomeinformationtothecustomer(serviceoutputs)e.g.theprovisionofweatherinformationand/oronsomechangesintherealworld(serviceeffects)e.g.theactualbookingofaseatonaflight;thefunctionalvalueoftheWebserviceisgivenbytheoutputsandeffectsassociatedtotheservicesthatcanberequestedthroughit.WecallthisfunctionalvaluethefunctionalcapabilityoftheWebservice[23].Inourmodel,aprovidercandescribethefunctionalcapabilityofitsWebserviceindifferentways,namely:a)onlysyntacticallyusingWSDL[5],b)assigningtheWebservicetooneormorecategories,and/orc)semantically,withdifferentlevelofdetail(onlyinputs,onlyresults,oralsotherelationbetweenboth).Thepublisherwillbefreetochooseamongthesetypesofdescriptionandtocombinethem.FordescribingWebservices,regardlessofthetypeofdescriptionused,weusetheWSMOframework[23]andtheWSML[9]familyoflanguages.However,ourmodelcouldworkwithotherframeworks.Inthissection,wepresentthealternativedescrip-tionsallowedinourmodelandhowtheyareincorporatedintotheWSMOframework.WedonotexplainhowWSDLWebservicesaredescribed;fordetailsonhowWSDLisusedtosyntacticallydescribethefunctionaWebserviceofferswereferto[5].2.1Semanticdescriptionwithinput-resultsrelationTheserviceprovidedbyaWebserviceand,thus,theresults(outputsandeffects)oftheWebserviceexecutiondependontheinformationgivenbythecustomertotheWebserviceasinputvalues,andonthestateoftheworldthatholdswhenarequestisissuedtotheWebservice.ThebookingprovidedbytheairlineWebservicementionedabovewilldepende.g.ontheflightdatagiventotheWebserviceandonseatavailability,whichispartofthestateoftheworld.Ifweabstractfromthepossiblycomplexinter-actionrequiredbyWebservicesforprovidingtheirfunctionality,aWebservicecanbeseenasafunctionthatmapsinputvaluesandthestateoftheworldtos