RDF Schema. Philippe Genoud, UFR IM2AG, UGA Manuel Atencia Arcas, UFR SHS, UGA

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1 RDF Schema Philippe Genoud, UFR IM2AG, UGA Manuel Atencia Arcas, UFR SHS, UGA 1

2 RDF Schema (RDF-S) Introduc)on Classes in RDF- S Proper@es in RDF- S Interpreta@on of RDF- S statements Descrip@on of classes and proper@es RDF and RDF- S in RDF- S Conclusion 2

3 Limitations of RDF RDF provides a standard way to make simple statements about web resources using named proper@es and values but with RDF we cannot express knowledge about proper@es and classes of resources, like, for example: that there exists a generaliza@on/specializa@on rela@onship between two classes that there exists a generaliza@on/specializa@on rela@onship between two proper@es that the subjects of a given property are of a par@cular type that the values of a given property are of a par@cular type 3

4 RDF Schema (RDF-S) W3C, T Berners-Lee, Ivan Herman 4

5 RDF Schema (RDF-S) Officially: "RDF Vocabulary Language" the term "Schema" has been kept for historical reasons à provides to user the possibility of defining vocabularies of terms) that they can later use inside RDF statements à an RDF vocabulary: class statements, property statements and between them à called ontologies 5

6 RDF Schema (RDF-S) RDF- S provides a type system for RDF in a way similar to type systems of object- oriented programming languages like Java classes ó types a[ributes ó proper@es instances ó resources inheritance ó hierarchical organiza@on of types but RDF- S is a descrip@on language, not a programming language: no methods 6

7 RDF Schema (RDF-S) RDF- S extends RDF with a schema vocabulary that allows defining the terms of specific vocabularies and the rela@ons between them. W3C recommenda@on : RDF Vocabulary Descrip@on Language h[p:// schema/ The RDF- S schema vocabulary is itself provided in the form of an RDF vocabulary Resources in the RDF Schema vocabulary are referred to by URIs with the namespace rdfs: schema# Examples of RDFS resources: rdfs:domain, rdfs:range, rdfs:class, rdfs:subclassof, rdfs:subpropertyof Seman@cs gives "extra meaning" to these par@cular proper@es and classes specifies how terms should be interpreted allows to draw inferences 7

8 RDF Schema (RDF-S) Vocabulary (schemas) wri[en in the RDF- S language are legal RDF graphs. any sobware that can process RDF can also interpret a RDF- S schema as a legal RDF graph but must be extended to understand the addi@onal built- in meanings of the RDF Schema terms. 8

9 RDF Schema (RDF-S) Classes in RDF- S Proper@es in RDF- S Interpreta@on of RDF- S statements Descrip@on of classes and proper@es RDF and RDF- S in RDF- S Conclusion 9

10 Classes in RDF-S A class is a set of objects/individuals sharing certain characteris@cs. A class is any resource declared to be of type rdfs:class using the property rdf:type. ex:motorvehicle rdf:type rdfs:class. Remember: the property rdf:type is used to state that a resource is an instance of a class. ex:van123 rdf:type ex:motorvehicle. rdfs:class rdf:type rdfs:class. The resource rdfs:class refers to the class of all RDF classes. 10

11 Classes in RDF-S A resource may be instance of more than one class. ex:motorvehicle rdf:type rdfs:class. ex:fourwheelvehicle rdf:type rdfs:class. ex:van123 rdf:type ex:motorvehicle ; rdf:type ex:fourwheelvehicle. The specializa@on rela@onship between two classes is described using the predefined rdfs:subclassof property. ex:motorvehicle rdf:type rdfs:class. ex:van rdf:type rdfs:class; rdfs:subclassof ex:motorvehicle. ex:truck rdf:type rdfs:class; rdfs:subclassof ex:motorvehicle. 11

12 Classes in RDF-S of rdfs:subclassof: each instance of the subclass must be an instance of the superclass. ex:vehicle rdf:type rdfs:class. ex:motorvehicle rdf:type rdfs:class ; rdfs:subclassof ex:vehicle. ex:van rdf:type rdfs:class; rdfs:subclassof ex:motorvehicle. 12

13 Classes in RDF-S è ex:van123 is an instance of ex:van and also an instance of ex:motorvehicle ex:motorvehicle rdfs:subclassof ex:van123 rdf:type ex:van ex:van123 rdf:type ex:motorvehicle. this triple is not in the original RDF data but it can be inferred from the of rdfs:subclassof RDFS environments will return this triple 13

Inference The seman@cs of RDF and RDF- S can be given in the form entailment rules.

graph, add this other triple" do it recursively un@l the graph does not change.

14 Inference The of RDF and RDF- S can be given in the form entailment rules. The RDF Seman@cs document has a list of 33 entailment rules: "if such triples are in the graph, add this other triple" do it recursively un@l the graph does not change. The relevant rule for our example: If: uuu rdfs:subclassof xxx. vvv rdf:type uuu. Then add: vvv rdf:type xxx.

A class may be a subclass of more than one class. Classes in RDF-S ex:motorvehicle rdf:type rdfs:class. ex:passengervehicle rdf:type rdfs:class ; rdfs:subclassof ex:motorvehicle.

15 A class may be a subclass of more than one class. Classes in RDF-S ex:motorvehicle rdf:type rdfs:class. ex:passengervehicle rdf:type rdfs:class ; rdfs:subclassof ex:motorvehicle. ex:van rdf:type rdfs:class, rdfs:subclassof ex:motorvehicle. ex:truck rdf:type rdfs:class; rdfs:subclassof ex:motorvehicle. ex:minivan rdf:type rdfs:class ; rdfs:subclassof ex:van, ex:passengervehicle. 15

16 RDF Schema (RDF-S) Classes in RDF- S Proper)es in RDF- S Interpreta@on of RDF- S statements Descrip@on of classes and proper@es RDF and RDF- S in RDF- S Conclusion 16

17 Properties in RDF-S All are described as instances of the class rdf:property. This class denotes the class of all RDF- S proper@es rdfs:domain, rdfs:range, and rdfs:subpropertyof describe how proper@es and classes are intended to be used together in RDF data. rdfs:domain specifies the type of all individuals that are the subject of statements using the described property. rdfs:range specifies the type of all individuals or the datatype of all literals that are the object of statements using the described property. 17

18 Properties in RDF-S example of property with a domain and range: ex:person rdf:type rdfs:class. ex:book rdf:type rdfs:class. ex:author rdf:type rdf:property ; rdfs:domain ex:book ; rdfs:range ex:person. ex:semanticwebfordummies ex:author ex:jeffpollock. ex:semanticwebfordummies rdf:type ex:book. ex:jeffpollock rdf:type ex:person. example of a property with a datatype range: ex:price rdf:type rdf:property ; rdfs:range xsd:integer. 18

19 Properties in RDF-S A property may have zero, one or more than one range declara@ons. 0 declara@ons: nothing is said about the values of the property. Anything (resource or literal) can be used as object of the property. 1 declara@on: this says that the objects of the property are instances (resp. literals) of the given class (resp. datatype) more than 1 declara@on: this says that the objects of the property are instances (resp. literals) of all classes (resp. datatypes) specified in the range declara@ons. ex:hasmother rdfs:range ex:female ; rdfs:range ex:person. exstaff:frank ex:hasmother exstaff:frances. must be both an instance of ex:female and of ex:person. 19

20 Properties in RDF-S A property can have zero, one or more than one domain declara@ons. 0 declara@ons: nothing is said about the subjects of the property. Any resource can be used as a subject of the property. 1 declara@ons: this says that the subjects of the property are instances of the given class. more than 1 declara@on: this says that the subjects of the property are instances of all classes specified in the domain declara@ons. ex:ismotherof rdfs:domain ex:female ; rdfs:domain ex:person. exstaff:frances ex:ismotherof exstaff:frank. must be both an instance of ex:female and of ex:person. 20

21 Properties in RDF-S the predefined rdf:subpropertyof property allows describing between property1 rdfs:subpropertyof property2. this means that property1 is a specializa@on of property2 then any two resources related using property1 are implicitly related by property2 ex:driver rdf:type rdf:property. ex:primarydriver rdf:type rdf:property. ex:primarydriver rdfs:subpropertyof ex:driver. exstaff:fred ex:primarydriver ex:companyvan exstaff:fred ex:driver ex:companyvan 21

22 Properties in RDF-S A property may be a subproperty of zero, one or more proper@es All RDF- S rdfs:range and rdfs:domain proper@es that apply to an RDF property will also apply to each of its subproper@es. ex:driver rdf:type rdf:property.; rdf:range ex:person ; rdf:domain ex:vehicle. ex:primarydriver rdf:type rdf:property ; rdfs:subpropertyof ex:driver. exstaff:fred ex:primarydriver ex:companyvan. exstaff:fred ex:driver ex:companyvan. exstaff:fred rdf:type ex:person. ex:companyvan rdf:type ex:vehicle. 22

23 Properties in RDF-S by default are defined independently from class ex:hasparent a rdf:property. ex:human a rdfs:class. hasparent has a global scope an can be used to describe instances of any class ex:john a ex:human; ex:hasparent ex:mary. ex:dog a rdfs:class. ex:daisy a ex:dog; ex:hasparent ex:amber. ex:book a rdfs:class. ex:semwebfordummies a ex:book; ex:hasparent ex:jeff. this flexibility facilitates the use of proper@es in situa@ons that might not have been an@cipated in the original descrip@on but proper@es can be miss- applied in inappropriate situa@ons 23

24 Properties in RDF-S with rdfs:domain et rdfs:range you can restrict the use of ex:hasparent a rdf:property. ; rdfs:domain ex:human; rdfs:range ex:human. ex:john a ex:human; ex:hasparent ex:mary.... but this introduces inflexibility and should be used with cau@on ex:daisy a ex:dog. ex:mary ex:hasparent ex:daisy. à ex:daisy is a Dog and a Human! any range defined for an RDF property applies to all uses of the property In RDF- S, it is not possible to define a specific property as having locally- different ranges depending on the class of the resource it is applied to. 24

25 Properties in RDF-S ex:livingorganism a rdfs:class. ex:human a rdfs:class. ; rdfs:subclassof ex:livingorganism. ex:dog ex:cat a rdfs:class. ; rdfs:subclassof ex:livingorganism. a rdfs:class. ; rdfs:subclassof ex:livingorganism. ex:hasparent a rdf:property; rdfs:domain??????; ex:livingorganism ; rdfs:range ex:livingorganism??????.. Not enough : a person could have a dog/car as parent ex:hashumanparent a rdf:property; rdfs:subpropertyof ex:hasparent ; rdfs:domain ex:human ; rdfs:range ex:human. Add new proper@es specializing hasparent ex:hascatparent a rdf:property ; rdfs:subpropertyof ex:hasparent ;... 25

26 RDF Schema (RDF-S) Classes in RDF- S Proper@es in RDF- S Interpreta)on of RDF- S statements Descrip@on of classes and proper@es RDF and RDF- S in RDF- S Conclusion 26

27 Interpretation of RDF-S statements RDF- S descrip@ons are not (necessarily) prescrip2ve like OOP languages are. OOP Language (Java) public Class Person{ private String name; } Person(String name) { this.name = name; } every instance of Person has a property (a[ribute) name and this a[ribute is unique every instance of Person has no other property than name RDF- S ex:person a rdfs:class. ex:hasname a rdf:property; rfs:domain ex:person; rdfs:range xsd:string; ex:john a ex:person; ex:hasname "Johnny Defool". it may have mul@ple values ex:john ex:hasname "Johnny". it may have other proper@es ex:john foaf:knows ex:mary. the property is not mandatory for instances of Person ex:paul a ex:person ; foaf:name "Paul White". RDF- S doesn't prescribe how the statements should be used by an 27 applica@on

28 RDF Schema (RDF-S) Classes in RDF- S Proper@es in RDF- S Interpreta@on of RDF- S statements Descrip)on of classes and proper)es RDF and RDFS in RDFS Conclusion 28

29 Description of classes and properties rdfs:label and rdfs:comment : allow a[aching labels and comments to classes and proper@es, or, in general, any kind of resource; their values are strings (literals); they are meant to be read by humans. rdfs:seealso : allows linking two resources that are related some way (e.g. the object resource provides addi@onal informa@on about subject resource); typically used in seman@c networks. rdfs:isdefinedby : used to indicate a resource defining the subject resource; typically used to specify the URI of the RDF vocabulary in which the subject resource is described. 29

30 RDF Schema (RDF-S) Classes in RDF- S Proper@es in RDF- S Interpreta@on of RDF- S statements Descrip@on of classes and proper@es RDF and RDF- S in RDF- S Conclusion 30

31 RDF and RDF-S in RDF-S RDF(S) Core classes: rdfs:resource, rdfs:class, rdfs:literal, rdf:property, rdf:statement Core proper)es for defining rela)onships: rdf:type, rdfs:subclassof, rdfs:subpropertyof Core proper)es for restric)ng proper)es: rdfs:domain, rdfs:range Reifica)on proper)es: rdf:subject, rdf:predicate, rdf:object Container classes: rdf:bag, rdf:seq, rdf:alt, rdfs:container U)lity proper)es: rdfs:seealso, rdfs:isdefinedby, rdfs:comment, rdfs:label 31

32 RDF and RDF-S in RDF-S RDF are defined using RDF- S (RDF rdf: < rdf- syntax- rdfs: < schema#>. rdf:type a rdfs:property ; rdfs:isdefinedby < rdf- syntax- ns#> ; rdfs:label "type"; rdfs:comment "The subject is an instance of a class." ; rdfs:range rdfs:class ; rdfs:domain rdfs:resource. 32

RDF and RDF-S in RDF-S RDF- S primi@ves are defined using RDF- S (RDF- S vocabulary) @prefix rdf: <http://www.w3.org/1999/02/22- rdf- syntax- ns#>. @prefix rdfs: <http://www.w3.org/2000/01/rdf- schema#>.

33 RDF and RDF-S in RDF-S RDF- S primi@ves are defined using RDF- S (RDF- S rdf: < rdf- syntax- rdfs: < schema#>. rdfs:resource rdf:type rdfs:class ; rdfs:isdefinedby < schema#> ; rdfs:label "Resource" ; rdfs:comment "The class resource, everything". rdfs:subclassof rdf:type rdfs:property ; rdfs:isdefinedby < schema#> ; rdfs:label "subclassof" ; rdfs:comment "The subject is a subclass of a class." ; rdfs:domain rdfs:class ; rdfs:range rdfs:class. This only says that rdfs:subclassof applies to classes and has a class as a a value. The namespaces do not provide the full defini@on of RDF and RDF- S. This is completed with the formal seman@cs based on entailment rules (see next chapters). 33

34 Exercise Give the RDF- S defini@ons of rdfs:domain and rdfs:range proper@es the reifica@on vocabulary (rdf:statement, rdf:predicate, rdf:subject and rdf:object) 34

35 RDF Schema (RDF-S) Classes in RDF- S Proper@es in RDF- S Interpreta@on of RDF- S statements Descrip@on of classes and proper@es RDF and RDF- S in RDF- S Conclusion 35

36 What does RDF-S give us? RDF A mechanism for publishing data. Single (simple) data model. Syntac@c consistency between names (IRIs). Low level integra@on of data. Mash the graphs together and we re done. RDF- S Ability to use simple schema/vocabularies when describing our resources. Consistent vocabulary use and sharing. Basic inference. 36

37 Limitations of RDF-S RDF- S is too weak to describe resources in sufficient detail. No localized range and domain constraints Can t say that the range of hasparent is Person when applied to Persons and Dog when applied to Dogs. No existence/cardinality constraints. Can't say that all instances of Person have a mother that is also a Person, or that Persons have exactly 2 parents. No transi)ve, inverse or symmetrical proper@es Can't say that ispartof is a transi@ve property, that haspart is the inverse of ispartof or that touches is symmetrical. 37

LECTURE 09 RDF: SCHEMA - AN INTRODUCTION

SEMANTIC WEB LECTURE 09 RDF: SCHEMA - AN INTRODUCTION IMRAN IHSAN ASSISTANT PROFESSOR AIR UNIVERSITY, ISLAMABAD THE SEMANTIC WEB LAYER CAKE 2 SW S16 09- RDFs: RDF Schema 1 IMPORTANT ASSUMPTION The following