Aplicatii Web bazate pe semantica, agenti si servicii

1. http://turing.cs.pub.ro/webs_07 Aplicatii Web bazate pe semantica, agenti si servicii Universitatea Politehnica BucurestiAnul universitar 2007-2008, MasterAdina Magda Florea

2. Curs 3 • XML • RDF • OWL

3. 1. XML • Sintaxa care descrie continutul; elemente XML • Corespunde unui arbore. Un element are marcaje (taguri) de inceput si sfarsit • Elementele pot avea unul sau mai multe atribute, fiecare cu o valoare asociata <temperature scale="Celsius"> • Un document XML are un singur element de top-level • Restrictii • Fiecare element care incepe cu un tag trebuie sa se termine cu unul • nu pot exista 2 atribute cu acelasi nume intr-un element

4. XML • XML defineste taguri specifice domeniului (spre deosebire de HTML – formatare) • Extensibilitate XML – orice vocabular specific domeniului poate fi construit • Nu este suficient pt a transmite semantica dar are potential in acest sens • Posibilitatea confuziei intre vocabulare => namespace

5. Namespaces • Identificare corecta = plasarea elementelor si atributelor intr-un spatiu de nume diferit (namespace, prescurtat ns) • Un ns este identificat prin URL lui specificat in doc XML • Declaratia de ns leaga un prefix local la un URI a ns <?xml version="1.0"?> <weather xmlns="http://www.temperature.org" xmlns:places= "http://www.temperature.org/places" <temperature scale="Celsius"> <value> 25</value> <error> 2 </error> <temperature/> <places:latitude>33.23</places:latitude> <places:longitude>155.23</places:longitudine> </weather> ns implicit prefix in ns

6. XML Schema • Descrie structura unui set de documente similare + elemente, atribute si valori implicite • Poate impune tipuri de date • O XML Schema este un document scris in XML care descrie structuri si valori permise pentru date valide XML (meta-document) • Un validator (XSV= XML Schema Validator) este un program care verifica un document XML daca este conform cu un XML Schema • xsd – XML Schema Definition • http://www.w3.org/2001/03/webdata/xsv

7. 2. RDF • Ofera o baza pt reprezentarea cunostintelor • Un limbaj simplu format din asertiuni (instructiuni) care permite reprezentarea cunostintelor, de ex resurse • RDF utilizeaza idei din reprezentarea cunostintelor dar foloseste Web pt a face cunostintele larg disponibile

8. De ce RDF? • XML • Specifica un arbore al documentului • Nu identifica continutul documentului • Permite reprezentari mltiple pentru acelasi continut • RDF exprima chiar continutul • RDF surprinde structura de esenta pe cand XML surprinde structura de suprafata • RDF descrie grafuri in general • Intelesul depinde de graf si nu de documentul care descrie graful

9. Resurse si literali • RDF permite descrierea resurselor • O resursa este un obiect • pt care se poate da o descriere • este identificat printr-un URI dar si printr-o descriere abstracta (nu neaparat se mapeaza la o adresa de retea) • Ex: docs, imags, videoclips, services, unele in afara web (oameni, obiecte) • Resursele se mapeaza conceptual pe entitati • Un literal este ceva mai simplu • O valoare (string, integer, ..) • Nu i se poate da o descriere • exista literali cu tip: sirul + referinta URI la o XML Schema care descrie tipul

10. Instructiuni sau triplete • RDF se bazeaza pe o gramatica simpla • Un document RDF este o multime de instructiuni sau triplete • Fiecare instructiune este formata din • Subiect: o resursa • Obiect: o resursa sau un literal • Predicat: o resursa (proprietate rdf:Property) • Subiectul este legat de obiect prin predicat (predicate binare)

11. Sintaxa • In principiu, RDF nu este legat de XML, dar este cea mai comuna sintaxa • Foloseste sintaxa standard a namespace din XML • Namespaces definite de standardul RDF • Abreviate tipic prin rdf si rdfs • Conceptul de baza – identificarea resurselor rdf:ID • rdf:ID este interpretat ca un fragment de identificator relativ la URI de baza pentru contextul curent • O valoare rdf:ID precedata de # corespunde unui URI relativ care, apendat la URI de baza, creaza URI absolut

12. Sintaxa • rdf:ID – introduce resursa ce se defineste • rdf:about – refera o resursa definita in alt loc • Se pot defini tipuri ale obiectelor prin rdf:type

13. Exemplu (folosind Dublin Core) <?xml version='1.0' encoding='UTF-8'?> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:dc="http://purl.org/dc/elements/1.1/"> <rdf:Description rdf:about="http://www.wiley.com/SOC"> <dc:title>Service-Oriented Computing</dc:title> <dc:creator>Munindar</dc:creator> <dc:creator>Michael</dc:creator> <dc:publisher>Wiley</dc:publisher> </rdf:Description> </rdf:RDF> • rdf:Description grupeaza instructiuni despre un subiect Set de metadate pentru descrierea resurselor

14. Reificare • Reificarea unui concept = posibilitatea de a-l referi • In RDF instructiunile sunt reificate pentru a permite altor instructiuni sa le refere • In acest scop se defineste rdf:Statement • Vazute ca resurse, toate instructiunile sunt de tipul • rdf:type rdf:Statement • Fiecare rdf:statement are 3 proprietati de baza: rdf:subject, rdf: object, rdf:predicate • Astfel se pot accesa cele 3 componente ale unei instructiuni • RDF – limbaj logic in care se pot exprima relatii binare si conjunctii (nu se pot exprima negatii si disjunctii) • Corespunde "exsitential-conjunctive logic"

15. 3. OWL • Web Ontological Language – specifica clase si proprietati intr-o forma bazata pe DL • O ontologie defineste clase si relatii intre clase • OWL trebuie sa permita colectarea informatiilor din surse multiple • Aceasta este partial realizata prin posibilitatea de a importa ontologii • OWL – presupunerea lumii deschise • Descrierea resurselor nu este limitata la un fisier sau un context • Clasa C1 poate fi definita in ontologia O1 dar poate fi extinsa in alte ontologii • C1 monotona • Nu se pot retrage informatii • Pot fi contradictorii

16. OWL • Definitii clase <owl:Class rdf:ID="Winery"/> <owl:Class rdf:ID="Region"/> <owl:Class rdf:ID="ConsumableThing"/> • Suporta superclase multiple <owl:Class rdf:ID="Mamifer"> <rdfs:subClassOf rdf:resource="#Animal"/> <rdfs:subClassOf rdf:resource="#Patruped"/> </owl:Class>

17. OWL • O clasa este definita prin proprietatile ei • Proprietati – o relatie binara intre 2 clase definita pe baza de domeniu si codomeniu (range) <owl:objectPropery rdf:ID="areParinte"> <rdfs:domain rdf:resource="#Animal"/> <rdfs:range rdf:resource="#Animal"/> </owl:objectPropery> • O proprietate poate avea sub-proprietati • Un individ se defineste ca un obiect al clasei <Mamifer rdf:ID="Rodo"> <areParinte> <Animal rdf:ID="#Cleo"/></areParinte> </Mamifer>

18. Namespaces • Declaratii de XML namespace care incep cu un tag rdf:RDF • Ofera modalitatea de a interpreta neambigu identificatori • O ontologie OWL tipica incepe cu o serie de declaratii de ns

19. Declaratii • Document OWL – elementul de top level este rdf:RDF • Apoi se declara de obicei ns cheie: OWL, RDF, RDF Schema, XML Schema si alte ns specifice domeniului • Urmeaza o asertiune cu elementul owl:Ontology care specifica ca este vorba de o ontologie • Urmeaza codificarea versiunilor si eventual importarea altor ontologii

20. Declaratii de namespaces <rdf:RDF xmlns ="http://www.w3.org/TR/2003/PR-owl-guide-20031215/wine#" xml:base ="http://www.w3.org/TR/2003/PR-owl-guide-20031215/wine#" xmlns:vin ="http://www.w3.org/TR/2003/PR-owl-guide-20031215/wine#" xmlns:food="http://www.w3.org/TR/2003/PR-owl-guide-20031215/food#" xmlns:owl ="http://www.w3.org/TR/owl-ref/#" xmlns:rdf ="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" xmlns:xsd ="http://www.w3.org/2001/XMLSchema#"> • Primele doua declaratii – ns asociate cu aceasta ontologie • Declara default namespace, indicand faptul ca numele fara prefixuri se refera la ontologia curenta • Declaratia a 3a identifica ns al ontologiei curente cu prefixul vin http://www.w3.org/TR/owl-guide/

21. Declaratii de namespaces <rdf:RDF xmlns ="http://www.w3.org/TR/2003/PR-owl-guide-20031215/wine#" xml:base ="http://www.w3.org/TR/2003/PR-owl-guide-20031215/wine#" xmlns:vin ="http://www.w3.org/TR/2003/PR-owl-guide-20031215/wine#" xmlns:food="http://www.w3.org/TR/2003/PR-owl-guide-20031215/food#" xmlns:owl ="http://www.w3.org/TR/owl-ref/#" xmlns:rdf ="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" xmlns:xsd ="http://www.w3.org/2001/XMLSchema#"> • A 4a declaratie identifica ns ontologiei suport food cu prefixul food: • A 5a declaratie spune ca in acest document elementele prefixate de owl: trebuie intelese ca referind obiecte din ns numit http://www.w3.org/TR/owl-ref# • Aceasta este o declaratie OWL conventionala utilizata pentru a introduce vocabularul OWL

22. Declaratii de namespaces <rdf:RDF xmlns ="http://www.w3.org/TR/2003/PR-owl-guide-20031215/wine#" xml:base ="http://www.w3.org/TR/2003/PR-owl-guide-20031215/wine#" xmlns:vin ="http://www.w3.org/TR/2003/PR-owl-guide-20031215/wine#" xmlns:food="http://www.w3.org/TR/2003/PR-owl-guide-20031215/food#" xmlns:owl ="http://www.w3.org/TR/owl-ref/#" xmlns:rdf ="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" xmlns:xsd ="http://www.w3.org/2001/XMLSchema#"> • OWL depinde de constructii definite de tipurile de date din RDF, RDFS si XML Schema. In acest document, prefixul rdf: se refera la elemente din ns xmlns:rdf ="http://www.w3.org/1999/02/22-rdf-syntax-ns#" • Urmatoarele doua declaratii de ns spun acelasi lucru despre tipurile de date din RDF Schema (rdfs:) si cele din XML Schema (xsd:)

23. Declararea entitatilor • In OWL referim (des) identificatorii utilizand valori de atribute. Acestea pot fi scrise complet, de exemplu: "http://www.w3.org/TR/2003/PR-owl-guide-20031215/wine#merlot" • sau utilizand abrevierile cu ajutorul definitiei unei entitati ENTITY, de exemplu: <!DOCTYPE rdf:RDF [ <!ENTITY vin "http://www.w3.org/TR/2003/PR-owl-guide-20031215/wine#" > <!ENTITY food "http://www.w3.org/TR/2003/PR-owl-guide-20031215/food#" > ]> • Dupa aceste definitii, putem scrie: "&vin;merlot" care se va expanda la: "http://www.w3.org/TR/2003/PR-owl-guide-20031215/wine#merlot"

24. Header-ul ontologiei <owl:Ontology rdf:about=""> <rdfs:comment>An example OWL ontology</rdfs:comment> <owl:priorVersion rdf:resource="http://www.w3.org/TR/2003/CR-owl-guide-1a/wine"/> <owl:imports rdf:resource="http://www.w3.org/TR/2003/PR-owl-guide-1b/food"/> <rdfs:label>Wine Ontology</rdfs:label> ... </owl:Ontology> • owl:Ontology colecteaza meta-date despre ontologie • owl:imports include (importa) o ontologie referita (poate esua)

25. Clase • Clasele definesc o multime de obiecte (instante) • Clasele OWL corespund conceptelor din DL • owl:Class– definita ca o subclasa a rdfs:Class • Toate clasele OWL sunt membrii ai owl:Class • O clasa predefinita owl:Thing este varful ierarhiei de clase (T) • owl:Nothing – predefinita: nu are instante, este o subclasa a oricarei clase ()

26. Clase • Cateva exemple simple: <owl:Class rdf:ID="Winery"/> <owl:Class rdf:ID="Region"/> <owl:Class rdf:ID="ConsumableThing"/> • rdf:ID defineste numele clasei • In cadrul documentului Region poate fi referit astfel: • rdf:resource="#Region" • <rdf:about="#Winery"/> poate fi utilizat pentru a referi clasa "Winery" pentru extindere/rafinare

27. Subclase • Subclasele introduc o relatie de subsumare <owl:Class rdf:ID="Pasta"> <rdfs:subClassOfrdf:resource="#ConsumableThing"/> ... </owl:Class> • In DL echivalent cu Pasta ConsumableThing • Rafinare <owl:Classrdf:about="Pasta"> <rdfs:subClassOf rdf:resource="#EdibleThing"/> ... </owl:Class> Pasta EdibleThing

28. Indivizi • Descriu membrii ai clasei • Declaratie individ cu numele CentralCoastRegion ca un membru al clasei Region <Region rdf:ID="CentralCoastRegion"/> • CentralCoastRegion: Region • Aceasta este echivalent cu <owl:Thing rdf:ID="#CentralCoastRegion"> <rdf:type rdf:resource="#Region"/> </owl:Thing> • rdf:type este o proprietate RDF care leaga un individ de clasa in care este membru

29. Indivizi <Region rdf:ID="SantaCruzMountainsRegion"> <locatedIn rdf:resource="#CaliforniaRegion"/> </Region> <Winery rdf:ID="SantaCruzMountainVineyard"/> <CabernetSauvignon rdf:ID="SantaCruzMountainVineyardCabernetSauvignon"> <locatedIn rdf:resource="#SantaCruzMountainsRegion"/> <hasMaker rdf:resource="#SantaCruzMountainVineyard"/> </CabernetSauvignon> <VintageYear rdf:ID="Year1998"> <yearValue rdf:datatype="&xsd;positiveInteger"> 1998 </yearValue> </VintageYear>

30. Proprietati • Exista 2 tipuri de proprietati: • Proprietati obiect • instante a owl:ObjectProperty • leaga instantele a 2 clase • domeniul si codomeniul = o instanta a owl:Class si sunt owl:Thing (daca nu se specifica altfel) • Proprietati tip de date • instante a owl:DatatypeProperty • leaga instantele unei clase de instante ale unui tip de date • domeniul este la fel, codomeiul este o instanta a rdfs:DataType si este owl:DataRange • RDF rdf:Property (refera o proprietate ca un URI) – in OWL se separa pred(x,y) – x: inst clasa y: inst clasa pred(x,y) – x: inst clasa y: inst tip de date

31. Proprietati obiect • O secventa de elemente OWL sunt legate (implicit) conjunctiv • Exemple proprietati obiect <owl:ObjectProperty rdf:ID="madeFromGrape"> <rdfs:domain rdf:resource="#Wine"/> <rdfs:range rdf:resource="#WineGrape"/> </owl:ObjectProperty> madeFromGrape.T Wine T madeFromGrape.WineGrape

32. Proprietati si subproprietati • rdfs:subPropertyOf • rdfs:domain • rdfs:range • rdfs:equivalentProperty • rdfs:inverseOf – numai pt proprietati obiect <owl:ObjectProperty rdf:ID="livesIn"> <rdfs:domain rdf:resource="#Animal"/> <rdfs:range rdf:resource="#Location"/> <rdfs:subPropertyOf rdf:resource="#hasHabitat"/> <rdfs:equivalentProperty rdf:resource="#hasHome"/> </owl:ObjectProperty>

33. hasColor hasWineDescriptor T hasColor.WineColor hasWineDescriptor WineDescriptor Wine hasColor WineColor Alt exemplu prop. obiect <owl:Class rdf:ID="WineDescriptor"/> <owl:Class rdf:ID="WineColor"> <rdfs:subClassOf rdf:resource="#WineDescriptor"/> ... </owl:Class> <owl:ObjectProperty rdf:ID="hasWineDescriptor"> <rdfs:domain rdf:resource="#Wine"/> <rdfs:range rdf:resource="#WineDescriptor"/> </owl:ObjectProperty> <owl:ObjectProperty rdf:ID="hasColor"> <rdfs:subPropertyOf rdf:resource="#hasWineDescriptor"/> <rdfs:domain rdf:resource="#Wine"/> <rdfs:range rdf:resource="#WineColor"/> </owl:ObjectProperty>

34. Proprietati tip de date • Exprima relatii intre instante de clase, literali RDF si tipuri de date XML Schema • Toate masinile OWL trebuie sa suporte cel putin tipurile de date: • xsd:integer si xsd:string • Exemplu <owl:DatatypeProperty rdf:ID="yearValue"> <rdfs:domain rdf:resource="#VintageYear"/> <rdfs:range rdf:resource="&xsd;positiveInteger"/> </owl:DatatypeProperty> • yearValue leaga owl:Thing la valori intregi pozitive

35. Constructori de clase • Cum se construieste o clasa? (a) Prin specificarea unui nume de clasa <owl:Class rdf:ID="WineDescriptor"/> (b) Prin specificarea nume clasa + descendenta <owl:Class rdf:ID="WineColor"> <rdfs:subClassOf rdf:resource="#WineDescriptor"/> </owl:Class> (c) combinatie de operatori logici: owl:IntersectionOf ( ), owl:unionOf ( ), owl:complementOf ( ) sau enumerareowl:oneOf (enumerare toti indivizii) Se foloseste in general cu tipul rdf:parseType='Collection' (d) Restrictii asupra proprietatilor = mecanism puternic

36. Combinatie de operatori logici <owl:Class rdf:ID="WhiteBurgundy"> <owl:intersectionOf rdf:parseType="Collection"> <owl:Class rdf:about="#Burgundy"/> <owl:Class rdf:about="#WhiteWine"/> </owl:intersectionOf> </owl:Class> <owl:Class rdf:ID="WhiteWine"> <owl:intersectionOf rdf:parseType="Collection"> <owl:Class rdf:about="#Wine"/> <owl:Restriction> <owl:onProperty rdf:resource="#hasColor"/> <owl:hasValue rdf:resource="#White"/> </owl:Restriction> </owl:intersectionOf> </owl:Class>

37. Combinatie de operatori logici <owl:Class rdf:ID="Fruit"> <owl:unionOf rdf:parseType="Collection"> <owl:Class rdf:about="#SweetFruit"/> <owl:Class rdf:about="#NonSweetFruit"/> </owl:unionOf> </owl:Class> Diferit de: <owl:Class rdf:ID="Fruit"> <rdfs:subClassOf rdf:resource="#SweetFruit"/> <rdfs:subClassOf rdf:resource="#NonSweetFruit"/> </owl:Class> care defineste Fruit ca intersectia intre SweetFruit si NonSweetFruit, care poate fi vida

38. Combinatie de operatori logici <owl:Class rdf:ID="ConsumableThing"/> <owl:Class rdf:ID="NonConsumableThing"> <owl:complementOf rdf:resource="#ConsumableThing"/> </owl:Class> <owl:Class rdf:ID="NonFrenchWine"> <owl:intersectionOf rdf:parseType="Collection"> <owl:Class rdf:about="#Wine"/> <owl:Class> <owl:complementOf> <owl:Restriction> <owl:onProperty rdf:resource="#locatedIn"/> <owl:hasValue rdf:resource="#FrenchRegion"/> </owl:Restriction> </owl:complementOf> </owl:Class> </owl:intersectionOf> </owl:Class>

39. Enumerare <owl:Class rdf:ID="WineColor"> <rdfs:subClassOf rdf:resource="#WineDescriptor"/> <owl:oneOf rdf:parseType="Collection"> <owl:WineColor rdf:about="#White"/> <owl:WineColor rdf:about="#Rose"/> <owl:WineColor rdf:about="#Red"/> </owl:oneOf> </owl:Class>

40. Restrictii • Construirea claselor pe baza restrictiilor aplicate proprietatilor • Obiectele are satisfac restrictia asupra proprietatii (proprietatilr formeaza o clasa anonima • owl:Restriction – subclasa a owl:Class • O restrictie poate fi de 2 tipuri • owl:ObjectRestriction – se aplica pe o proprietate obiect • owl:dataRestriction – se aplica pe o proprietate tip de date • Proprietatea asupra careia se aplica restrictia este specificata prin owl:Property • owl:someValuesFrom • owl:hasValue • owl:minCardinality • owl:maxCardinality

41. Wine Food:PotableLiquid ≥1 madeFromGrape Restrictii <owl:Class rdf:ID="Wine"> <rdfs:subClassOf rdf:resource="&food;PotableLiquid"/> <rdfs:subClassOf> <owl:Restriction> <owl:onProperty rdf:resource="#madeFromGrape"/> <owl:minCardinality rdf:datatype="&xsd;nonNegativeInteger"> 1 </owl:minCardinality> </owl:Restriction> </rdfs:subClassOf> ... </owl:Class> • Zona verde defineste o clasa anionima care reprezinta lucrurile ce au o proprietate madeFromGrape (apar in cel putin o astfel de proprietate) • Definitia clasei Wine spune ca lucrurile care sunt Wine sunt de asemenea membrii ai acestei clase anonime • Fiecare individ Wine trebuie sa participe in cel putin o relatie madeFromGrape

42. USACompany Company locatedIn:USA Restrictii <owl:Class rdf:ID="USACompany"> <rdfs:subClassOf rdf:resource="#Company"/> <rdfs:subClassOf> <owl:Restriction> <owl:onProperty rdf:resource="#locatedIn"/> <owl:hasValue rdf:resource="#USA"/> </owl:Restriction> </rdfs:subClassOf> </owl:Class>

43. Restrictii <owl:Class rdf:ID="EuropeanCompany"> <rdfs:subClassOf rdf:resource="#Company"/> <rdfs:subClassOf> <owl:Restriction> <owl:onProperty rdf:resource="#locatedIn"/> <owl:someValuesFrom rdf:resource="#EuropeanCountry"/> </owl:Restriction> </rdfs:subClassOf> </owl:Class> EuropeanCompany Company locatedIn.EuropeanCountry

44. Constructori de clase

45. Exemplu <owl:Class> <owl:intersectionOf rdf:parseType="Collection"> <owl:Class rdf:about="#Person"/> <owl:Restriction> <owl:onProperty rdf:resource="#hasChild"/> <owl:allValuesFrom> <owl:unionOf rdf:parseType="Collection"> <owl:Class rdf:about="#Doctor"/> <owl:Restriction> <owl:onProperty rdf:resource="#hasChild"/> <owl:someValuesFrom rdf:resource="#Doctor"/> </owl:Restriction> </owl:unionOf> </owl:allValuesFrom> </owl:Restriction> </owl:intersectionOf> </owl:Class> Person hasChild.(Doctor  hasChild.Doctor)

46. Axiome Clase Indivizi Proprietati

47. Specii OWL • OWL Lite – in principal ierarhii si restrictii smple • e.g., cardinalitati numai 0 or 1, fara disjunctii • OWL DL – expresivitate maxima dar pastrand completitudinea calcului si decidabilitate • OWL Full – libertatea sintactica a RDF fara garantii computationale • e.g., in OWL Full o clasa poate fi tratata simultan ca o colectie de indivizi si ca un individ

48. Exemplu ontologie OWL • Studentii opteaza pt cursuri, cursurile sunt oferite de departamente (unic), CS este un departament, un student trebuie sa urmeze cel putin un curs, un student full-time trebuie sa umeze intre 3 si 5 cursuri, un student full-time la CS <owl:Class rdf:ID="Student"/> <owl:Class rdf:ID="Course"/> <owl:Class rdf:ID="Department"/> <Department rdf:ID="CS"/>

49. Exemplu ontologie OWL <owl:ObjectProperty rdf:ID="takes"> <rdfs:domain rdf:resource="#Student"/> <rdfs:range rdf:resource="#Course"/> </owl:ObjectProperty> <owl:Restriction> <owl:onProperty rdf:resource="#takes"/> <owl:minCardinality rdf:datatype="&xsd;nonNegativeInteger"> 1 </owl:minCardinality> </owl:Restriction> • O clasa anonima in care membrii urmeaza cel putin un curs. Stiind ca domeiul este Student se poate infera ca este o subclasa a Student. • Nu se spune insa ca toti studentii urmeaza cel putin un curs!

50. Student <owl:Class rdf:about="Student"> <rdfs:subClassOf> <owl:Restriction> <owl:onProperty rdf:resource="#takes"/> <owl:minCardinality rdf:datatype="&xsd;nonNegativeInteger"> 1 </owl:minCardinality> </owl:Restriction> </rdfs:subClassOf> </owl:Class>