©CopyrightJASSS

J.GaryPolhill(2015)

ExtractingOWLOntologiesfromAgent-BasedModels:ANetlogoExtension

JournalofArtificialSocietiesandSocialSimulation 18(2)15<http://jasss.soc.surrey.ac.uk/18/2/15.html>

Received:09-Oct-2014Accepted:24-Feb-2015Published:31-Mar-2015

Abstract

UsingOWLontologiestorepresentthestateandstructureofasimulationatanyonetimehasbeenarguedtoimprovethetransparencyofasocialsimulation,onthebasisthatthisinformationisthennotembeddedinthesourcecodeofthemodel,orinthecomputer'smemoryatrun-time.Shouldtransparencyofsuchaformbedesirable,itwouldbepreferabletoenableitbyextractingtheinformationautomaticallyfromarunningmodel.However,semanticdifferencesbetweentraditionalobject-orientedprogramminglanguagesanddescriptionlogicsposeanobstacletothis.ThispaperpresentsargumentsthatNetlogodoesnothavethesamesemanticchallengestoautomatedontologyextraction,anddescribesanextensiontoNetlogo(5.0)usingtheOWL-API(3.1.0)thatextractsstateandstructureontologiesfromanexistingNetlogomodel.Theextensionisfreelyavailablefromhttps://github.com/garypolhill/netlogo-owl.

Keywords:Netlogo,OWL,OWL-API,Ontology,Transparency

Introduction

1.1 Socialsimulationisoftenarguedtobemoretransparentthanotherapproachestomodellingsocialsystems(e.g.Galánetal.2009).Thetransparencyofasocialsimulationcanrefertotheabilitytorelatethestateandstructureofasimulationtothoseofthetargetsystemitisintendedtorepresent(e.g.Leydesdorff2001),butalsototherelationshipbetweenexpressionsinthesourcecodeandpropertiesofthetargetsystem(e.g.Taylor2003).Ingeneral,transparencyinthiscontextmaybeconceivedastheabilityofsomeoneotherthanthoseimmediatelyinvolvedinamodel'sconstructiontounderstandwhatitisdoing(e.g.Polhill&Gotts2009).However,asJanssenetal.(2008)pointout,whilstfulltransparencyisideal,'translucency'–inwhichthereisapartialexposureoftheimplementation–mayoftenbeallthatispractical.Indeed,sometimesthelattermaybepreferred;forexample,whendiscussingcertainaspectsofthemodelininter-ortrans-disciplinaryteams.

1.2 Whilstcomputerprogramminglanguagescanbereasonablyarguedtoefficientlyandformallydescribealgorithms,extractingthestructureofasimulation(theclassesofentityinthemodel,thepropertiestheyhave,andtherelationshipstheyhavewithotherentities)fromitssourcecodecanbechallenging.Inanobject-orientedmodel,thestructuremaybedistributedacrossseveralclassfiles,withnoimmediatelyobviouswaytodeterminewhichclassesareontologicallysignificant,andwhicharetheretoprovidefunctionalitynotalreadyprovidedbythelanguageAPIoranyprogramminglibrariesused.AlthoughextractingUMLdiagramsfromobject-orientedcodecanbeautomated,thereisthefurtherproblemthatinheritanceinobject-orientedmodelsreflectscompilerandprogrammerconvenience,ratherthancommon-senseunderstandings(LaLonde&Pugh1991).Ifthereisanacceptancethatlogicsareformalisationsofcommon-senseunderstandings,thenforthepurposesoftransparency(ortranslucency)ratherthanprogramming,theidealwouldbethatthemodelstructureisrepresentedusingaxiomsofdescriptionlogics.

1.3 Semanticdifferencesbetweenclassicalobject-orientedprogramminglanguagesanddescriptionlogicshavebeenhighlightedbyPolhillandGotts(2009),withreferencetoLalondeandPugh's(1991)distinctionsamongthethreeinheritancerelationssubtype,subclassandis-a.Ofthesethree,thefirstisforcompilerconvenienceincheckingtypesinvolvedinoperations(interfacesinJava),thesecondforprogrammerconvenienceinfacilitatingcodere-use(classesinJava),whilstthethirdreflectsdescriptive,logicalmeaningsthatareofprimaryinterestfromanontologicalpointofview.Thesedifferencesmeanthatdirectontologylearningfrommodelsourcecodeisnotguaranteedinobject-orientedprogramminglanguages.

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1.4 Netlogo(Wilensky1999)modelsdonothavetheseissuesbecauseNetlogoisnotanobject-orientedprogramminglanguage,andthereisnoinheritanceamongthelanguage'smainentity('agent'inNetlogoterminology)types,whichareknownas'breeds'.Thefacilityforexplicitrepresentationofrelationships(or'links')amongagents,ratherthanencapsulatingassociationsinclassesasinobject-orientedlanguages,furthercontributestoenablingautomaticontologylearningfromNetlogomodelcode,though,asdiscussedlater,doingsoimposesaparticularprogrammingstyleontheimplementation.

1.5 Netlogo'sextensionfacilityenablessoftwaretobewrittenthatprovidesfunctionalityfromwithinNetlogotoautomaticallyextractanOWL(Horrocksetal.2003)orOWL2(CuencaGrauetal.2008)ontologyfromthemodel.OWLisapopularlyusedlanguageforexpressingontologies,whichhascorrespondenceswithdescriptionlogicsthatdependonthesublanguageused.ThemappingisshowninTable1.

Table1:MappingfromNetlogosyntaxtoOWLontologytypes.

Netlogosyntax OWLtype(s) Commentsbreed Class BreedsinNetlogo,likeclassesinOWL,arenotnecessarilydisjoint–

agentscanchangebreedusingthesetbreedcommand.directed-link-breed(no'own')

ObjectProperty Foralllinkbreeds,thereisnosyntaxtoconstrainthebreedsofagentthatareateitherendofthelink,meaningthatdomainsandrangesforlinkscannotbeinferredfromthecode.Ifthelinkbreeddoesnothaveanyofits'own'variables,itcanbedeclareddirectlyasanobjectproperty…

directed-link-breed(with'own')

ClassandObjectProperty

…otherwisethelinkmustbereified,andtwoobjectpropertiesusedtolinkthebreedsthatcanbeconnectedinthisway.Theobjectpropertygoingintotheclassrepresentingthepropertycanbedeclaredinversefunctional;theobjectpropertygoingoutcanbedeclaredfunctional.ApropertychaincanbeusedtorepresentthelinkasawholeiftheontologyisinOWL2.

undirected-link-breed

ObjectPropertyorClassandObjectProperty

Inadditiontothepointsapplyingtodirectedlinkbreeds,objectpropertiescorrespondingtoundirectedlinkbreeds(inthecaseofreifiedlinks,thiswillapplytothechain)canbedeclaredsymmetricinOWL.IftheontologyisinOWL2,alllinkscanbedeclaredasirreflexiveasNetlogodoesnotpermitanagenttolinktoitself.

breeds-own DataProperty Thedomainofthedatapropertycanbedeclaredtobetheclasscorrespondingtothebreed.However,sinceNetlogodoesnothavetypedvariables,thedatarangecannotbeautomaticallyinferred.Notethatdifferentbreedscanhavethesamevariable.

link-breeds-own

DataProperty Thedomainofthedatapropertycanbedeclaredtobetheclasscorrespondingtothelinkbreed.Notethatdifferentlinkbreedscanhavethesamevariable,butavariablecannotbesharedbetweenlinkbreedsandbreeds.

agent Individual AgentsinNetlogocanbeassertedasindividuals,andmembersoftheclasscorrespondingtothebreedofwhichtheyarecurrentlyamember.

1.6 Intherestofthispaper,anextensiontoNetlogoimplementingthesemappingsispresented,togetherwithanillustrationbasedontheCEDSS(CommunityEnergyDemandSocialSimulator)model,builtaspartoftheGILDED(Governance,Infrastructure,LifestyleDynamicsandEnergyDemand)FrameworkProgramme7project(http://gildedeu.hutton.ac.uk/).

TheNetlogoExtension

2.1 TheowlextensiontoNetlogowaswrittentoimplementthemappingsinTable1.TheextensioniswrittenforNetlogo5.0,andconsistsofthefileowl.jar.This,togetherwithversion3.1.0oftheOWL-API(Bechhoferetal.2003;Horridgeetal.2007;http://owlapi.sourceforge.net/),whichisavailableundertheGNULibraryGeneralPublicLicence,shouldbeplacedinasubdirectorynamed'owl'ofthedirectoryinwhichthe.nlogofileusingtheowlextensionislocated.Thefile'owl.zip'–thereleaseversionoftheextension,containsowl.jarandtheOWL-API(owlapi-bin.jar),readyforuse.Topermanentlyinstalltheextension,putitintheextensionsfolderoftheNetlogoapplicationsdirectory.

2.2 TheextensionmakesavailableanumberofcommandstoaNetlogomodelcontainingthefollowingcommand(typically,nearthebeginningofthecode):

extensions[owl]

Thecommandsaregiveninapproximateorderinwhichtheymustoccurduringexecutionofthemodel.Specifically,

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owl:domain,owl:rangeandowl:importscannotbeusedafterowl:model,andowl:structureandowl:statemayonlybeusedafterowl:model.

2.3 Thecommandsassumeadistinctionbetweenthestructureandthestateofthemodelandcorrespondingontologies.Anontologydescribingthestructureofamodelconsistsofterminology(T-box)axiomsdescribingthekindsofentitythatthemodelcontains(OWLclasses),propertiestheyhave(OWLdataproperties)andrelationshipstheymayhavewithothertypesofentity(OWLobjectproperties).Bycontrast,anontologydescribingthestateofamodelappliestoaparticularsnapshotofaninstanceofitrunningatonetime.Thestateontologyimportsthestructureontology,andthenaddsassertion(A-box)axiomsaboutthespecificinstancesofthevariousclassesofentitythatexistinthemodelwhenthesnapshotistaken.

owl:domainlink-breedbreed

2.4 Theowl:domaincommandtakestwoarguments.Thefirstisthe(string)nameofalink-breed,andthesecondisthe(string)nameofabreed.ThecommandcausesanassertiontobemadeintheontologythattheOWLclasscorrespondingtothebreedisinthedomainoftheOWLobjectpropertycorrespondingtothelink-breed.

2.5 Thiscommandwillnotaffectyourmodel(thatistosay,whilethemodelruns,nocheckwillbemadeofthelink-breedthatonlyagentsofthespecifiedbreedareinthedomainofthelink-breed).

owl:rangelink-breedbreed

2.6 Theowl:rangecommandtakestwoarguments.Thefirstisthe(string)nameofalink-breed,andthesecondisthe(string)nameofabreed.ThecommandcausesanassertiontobemadeintheontologythattheOWLclasscorrespondingtothebreedisintherangeoftheOWLobjectpropertycorrespondingtothelink-breed.

2.7 Justasforowl:domain,owl:rangedoesnotcauseanycheckstobemadewhilethemodelrunsthatonlyagentsofthespecifiedbreedareintherangeofthelink-breed.

owl:importsIRI…

2.8 Theargument(s)totheowl:importscommandarestringscontainingInternationalisedResourceIdentifiersforontologiesthatthemodelstructureontologyistoimport.Again,thisdoesnotaffectthemodelinanyway,orcauseanycheckstobemade,butallowstheontologytobecreatedwiththeimportsinplacereadyforusewithontologyvisualisation,reasoningandanalysistools.

owl:modelIRI

2.9 DefinetheInternationalisedResourceIdentifierforthemodelstructureontology,whichiscontainedinthestringargument.AllontologieshaveanIRI,whichconstitutesanidentifierfortheontology.AlthoughtheIRIisusuallyawebaddress,itisnotnecessarilythecasethatthefilewillexistatthatwebaddress(thoughideallyitwould)–theIRIisjustaname.

2.10 Asstatedabove,allowl:domain,owl:rangeandowl:importscommandsmustexecutebeforeowl:modelisexecuted,andnoowl:structureorowl:statecommandmayexecuteuntilowl:modelhasexecuted.

owl:optionsoption-string…

2.11 Setoptionsforcreatingstructureandstateontologies.Threeoptionstringsareavailable:

"owl2",whichwilladdOWL2axiomstotheontologywhererelevant;"relations",whichwilladdaxiomsassertingrelationshipattributes(e.g.symmetric,andif"owl2"isspecified,irreflexiveandasymmetric)topropertyassertionsintheontologywhererelevant;and"no-patches",whichsuppressesspatialaxioms.SpatialaxiomsincludetheassertionofalocationobjectpropertywithrangePatch,andhencethedeclarationofthelatterasaclass.

Theoption"none"(thedefault)canbeusedtoindicatethatnoneoftheoptionsaboveapplies.Theowl:optionscommandcanberunmorethanonce,overridinganyoptionsselectedinearliercalls;subsequentcallstoowl:structureandowl:statewillrespecttheoptionsselected.

owl:structurefile-name

2.12 Saveamodelstructureontologytothefilenamegivenasarguments.ThelogicalIRIoftheontologywillbethatspecifiedusingtheowl:modelcommand.NotethatforvisualisationsoftwaresuchasOntoViztoshowalinkasanobjectpropertyintheresultingdiagram,bothowl:domainandowl:rangemusthavebeenspecified.(Thesoftwarewouldotherwisenotknowwhichclassestodrawthelinkfromandtorespectively.)

owl:statefile-nametime-step(experimental)

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2.13 Saveanontologyofthecurrentstateofthemodeltothefilename.ThelogicalIRIforthestateontologywillbeconstructedfromthemodelIRIspecifiedbytheearlierowl:modelcommandandthetime-stepgivenassecondargumenttothiscommand.Specifically,any.owlsuffixwillberemovedfromthemodelIRI,andthen"-state-"appended,followedbythetime-step,followedbytheextensionstringifgiven,followedbythe.owlsuffixifthemodelIRIhaditoriginally.

2.14 Forexample,themodelIRI"http://www.gildedeu.org/ontologies/CEDSS-3.3.owl"giventheargument7forthetime-step,wouldproduceastateontologyIRI"http://www.gildedeu.org/ontologies/CEDSS-3.3-state-7.owl".(Notethatthelinkshavedifferenttargetsfromthoseshown.)

2.15 Thefile-nameargumentgivesaphysicallocationtosavetheontologyto.Ifitdoesnotendwith".owl",thenthenameoftheresourceinthegeneratedstateontologyIRIisappendedtothefile-nameargumenttoproducethefinallocation.Forexample,withthestateontologyIRIabove(ifticks=7):

owl:state"/var/tmp/"ticks

willsavetheontologyto/var/tmp/CEDSS-3.3-state-7.owl.

2.16 Anexceptionisthrownifanattemptismadetooverwriteanexistingfile.

2.17 Theowl:statecommandcanbequitedemandingonresourcesdependingonthesizeofthemodel.Aswellasthefilesavedbeingpotentiallyquitelargeinsize,thecommandcantakeseveralminutestosearchthroughalltheelementsinthemodel,andmaycrashwithheaperrorsifNetlogoisnotrunwithsufficientmemorygiventotheJavavirtualmachine.(TheexampleinFigure3belowtakes1minuteorsoonamachinewitha2.8GHzIntelCorei7processor,requires8GofRAMfortheJavavirtualmachine,andtheresultingOWLfile(inRDF/XMLformat)occupies650Morsoofdiskspaceifnotcompressed.)

Illustration

3.1 TheCEDSS(CommunityEnergyDemandSocialSimulator)modelwasbuilttosimulatedomesticenergyusepatternsinasmallcommunity(e.g.ahousingestateoravillage),andisbasedonanearlierprototypemodelwiththeacronymABMED(AgentBasedModelofEnergyDemand;Gotts2009).Itrepresentshouseholdsasagents,wholiveindwellings,andhaveaportfolioofappliancestheyuseforspaceandwaterheating,andentertainment.Usingarepresentationofthepsychologicaltheoryof'goalframes'(Lindenberg&Steg2007),inwhichconsumerdecisionsarebasedarounddifferentmodesofbehaviour(inthiscase,hedonistic,egoistic,andbiospheric),CEDSSagentsdecidehowtoreplacebrokenappliances,andwhethertobuyanynewappliances.Interactionsarebasedaroundagentsvisitingotherhousesintheirsocialnetwork.Visitoragentsobserveandpotentiallydesireappliancestheydon'townthattheirhostspossess,andadjustgoalframeparameterstomaketheprobabilitiesofdifferentmodesofbehaviourmoresimilartothoseoftheirhosts.

3.2 ThefollowingproceduredemonstratestheuseofsomeoftheaboveontologyfeaturestosaveastructureontologyfromCEDSS:

Figure1.ExampleproceduretoextractastructureontologyfromCEDSS.

3.3 UsingtheOntoViz(Sintek2007)plug-inforProtégé3,aDOTgraphcanbecreatedoftheresultingontology,which(withsomeminoreditingtosimplifythetext,enterdatatypesandhighlightreifiedlink-breedsinblue)isshowninFigure2.

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Figure2.OntologyextractedfromCEDSSvisualisedwithOntoViz.

Figure3.DiagramofalltheindividualsinastateontologyintheCEDSSmodel,renderedusingthesfdpcommandsuppliedwithGraphViz[1]andabespokeprogramtocreateanappropriatelyformatteddotgraphfromtheontology.Nodes(blackdots)areindividuals,colouredarcsareobjectproperties.Apartfromthedensegraphinthemiddle,theotherarcsshowupgrade

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pathsforinsulations,andlocation(built-inrelationshipagentshavewithpatches,whichwouldnothavebeenincludediftheno-patchesoptionhadbeenspecified).

Discussionandconclusion

4.1 WhilsttheontologyextractedfromtheNetlogocodemakessemanticsense,writinganewmodelwithaviewtousingtheextensionmayaffectthewaycertainconceptsarerepresented.Thetreatmentofallbreeds''own'variablesasdatapropertiesmeansthatanysuchvariablesthatcontainlistsorsetsofotheragentswillnotberepresentedasarelationshipintheresultingstructureontology,withtheextensionaspresentlywritten.Theeffectwouldbetoencouragetheexplicitrepresentationofrelationshipsusinglink-breeds.MappingfrombreedstoOWLclasseswouldalsoencouragemodeldeveloperstomakegreateruseofbreedsformodelentitiesthanotherwisetheymight.An'agent'mightnormallybethoughtofassomethingthatundertakesanaction,aconceptualisationthattendstoopposetherepresentationofinanimateentitiesasagents.ThismaybeundesirablefromsometheoreticalperspectivesiftheconceptofanagentinNetlogoistobetakenliterally(aviewthatwouldarguablybesomewhat'fundamentalist'incharacter),butisnotwithouttheoreticalprecedent(Dennett1971;Latour2005).

4.2 Theothersideofthiscoinisthatdifferentcodingstyleswillinfluencetheontologyextracted.SupposetwopeopleuseNetlogotoreimplementthesamemodel.Bothreimplementationsbehaveinthesameway(orwithadegreeofsimilaritycorrespondingtooneofWilenskyandRand's(2007)levels),butthedifferentapproacheachhasusedtorepresentthemodelusingNetlogodatastructuresandfeaturesmeansthattheontologiesextractedfromeachimplementationwillbedifferent.

4.3 Hereweusethesimpleexampleofamodelinwhichagroupofchildrenareplayingwithtoys.Eachchildhasatoy,and,dependingonwhichtoytheyhavewillgetboredwithitafteraspecifiednumberoftimestepsandtrytoswaptheirtoywiththatofoneoftheirfriendswhoisalsobored.Thereareconstraintsonwhichtoyscanbeswapped(seeTable2).Thenumberoftimestepsforwhicheachchildhasthetoytheyareplayingwithisrecorded,andisresettozeroaftereachswap.Theparametersofthemodelarethepercentagesofchildrenhavingeachtoyinitially,thenumberofchildren,andthenumberoffriendseachchildhas(whichisthesameforallchildren).Weareinterestedinthedistributionofthenumberofboredchildrenoverthetimeofthemodelrun,whichisahistogramofthenumberoftimestepsforwhichtherewerexboredchildren.

Table2:Tableoftoyparameters

Toy Timeuntilbored Canswapwith…marbles 3 blocks,bearblocks 4 marbles,bearbear 2 marbles,blocks,rag-dollrag-doll 1 bear

4.4 Therearevariouswaysthemodelcouldbeimplemented,buttohighlightthepotentialdifferencesincodingstyle,wechooseoneapproachmakingnouseofbreedsorlinks,andcontrastitwithacodingstylemoresuitableforusewiththeowlextension.Thetwoimplementationshaveslightlydifferentoutputafter500timesteps–exactnumericalsimilarity,despitecontrollingforseed,hasnotbeenachieved,butthedistributionsofnumbersofboredchildrenovertimeareverysimilar(Figure4).InFigure5,however,thedifferencebetweentheontologiestheextensionisabletoextractfromthetwoimplementationsisclear.

(a)(b)

Figure4.Screenshotsfromthetwoimplementationsusingthesameparameters.(a)Implementationnotusingbreedsorlinks;(b)implementationsuitableforowlextension(whichisalsoabletoshowwhoisplayingwithwhichtoy).After500time

steps,thedistributionsofboredchildrenshowninthehistogramsaresimilar,butthereareslightdifferences.

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(a)(b)

Figure5.Differenceinontologygeneratedbytheowlextensionforthetwoimplementations.(b)Showstheontologyfromtheimplementationdesignedtoworkwiththeowlextension.NotethatincontrasttoFigure2,thereifiedrelationshipPlayingshasnotbeencoloured,anddatatypeshavenotbeenmanuallyentered.Thisshowsmoreclearlywhattheowlextension

providesbydefault.

4.5 AsTable3shows,thereareconsiderabledifferencesinthewaytherepresentationinthetwoimplementationsissetup.Theleftcolumnrepresentationjustusesthedefaultturtlebreedandassignsitsomevariablestostoretheinformationusedbythemodel:alistoffriends,whichtoytheyareplayingwith,whetherornottheyarebored,andthelengthoftimetheyhavebeenplayingwiththecurrenttoy.Intherighthandcolumn,thecodeismoreexplicitaboutthemicroworld:therearebreedsfortoysandchildren,linkbreedsforwhoisafriendofwhom,whoisplayingwithwhattoy,andwhichtoyscanbeswappedwithwhichothers.Asaresult,thechildrenbreedhasonlytheBooleanstoringwhetherornottheyarebored.Therighthandrepresentationalsocontainsadditionalinformationaboutthetoys,withboredom-timestoringhowlongittakesforachildtogetboredwithplayingwithit.ThecodeinTable4showsthatthestrictimplementationnotusingabreedtorepresentthetoyshasmeantthatthisinformationishard-codedintothemodel,thoughtherecouldbewaysroundthisusing,forexample,thetableextensioninNetlogotoassociatethenameofthetoywiththetime.

Table3:Contrastingrepresentationsinthetwoimplementationsofthe'toy'model

Nobreedsorlinks Versionsuitableforowlextensionturtles-own[friendstoybored?time]

breed[toystoy]toys-own[nameboredom-time]

breed[childrenchild]children-own[bored?]

directed-link-breed[friendsfriend]

directed-link-breed[playingsplaying]playings-own[time]

undirected-link-breed[swapsswap]

Table4:Contrastingimplementationofdeterminingwhetherchildrenarebored

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4.6 Table4alsoshowsthattherecanbesomeawkwardsyntaxinthecodingstyleusedtomaketherepresentationinthemodelmoresuitablefortheowlextension.SinceNetlogodoesn'thavesyntaxforfunctionalrelationships,my-out-playingsmakesitunclearthateachchildcanonlyplaywithonetoyatatime.Arguably,forthosenotfamiliarwithNetlogo,thecodeontheleftisclearerabouttheconditionsunderwhichchildren(eveniftheyarecalledturtleshere)becomebored.Ontheotherhanditmakesnoreferenceto'playing'or'boredom-time',meaningthatforthosewithanunderstandingofNetlogosyntax,thecodeontherightis(functionalrelationshipquestionaside)arguablymoretransparentinthatthehardcodednumbersarereplacedwithavariabledescribingwhattheyaresupposedtomean.

4.7 Althoughthefactthatthesetwofunctionallysimilarimplementationshavedifferentontologiescouldbeseenasaweakness,itcouldequallybearguedthatthisisareflectionofvariationsintransparencyofcodingstyle.Thatis,twofunctionallysimilarimplementationscanstillbecomparedonthebasisofhowclearlytheirsourcecodereflectsthesystemtheyarerepresenting.WhetherthisextensiontoNetlogohasanyroletoplayinmakingsuchajudgementisdebatable,if,indeed,suchquestionsareanythingmorethanamatterofsubjectivepreferences.Insofarasthereareobjectivemeasuresoftransparency(anexampleofwhichcouldbetheeasewithwhichinferencescanbemadeusinginformationaboutthemodelstateorstructure),softwaresuchastheNetlogoextensionpresentedherecouldproveuseful.

AvailabilityandRequirements

ThesoftwareisavailableonGitHubunderaGNULesserGeneralPublicLicenceathttps://github.com/garypolhill/netlogo-owl.

ItrequirestheOWL-APIversion3.1.0availablefromSourceForgeathttp://sourceforge.net/projects/owlapi/files/OWLAPI(forOWL2.0)/3.1.0/.

Acknowledgements

ThisworkwasfundedbytheEuropeanCommissionSeventhFrameworkProgramme,grantagreementnumber225383,andtheScottishGovernmentRuralAffairsandtheEnvironmentPortfolioStrategicResearchTheme4(EconomicAdaptation).

Notes

1http://www.graphviz.org/

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