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Defining RDF Vocabularies: RDF Schema

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ex:MiniVan rdfs:subClassOf ex:Van. 7. A Vehicle Class Hierarchy. 8. A ... ex:MiniVan rdf:type rdfs:Class . ex:PassengerVehicle rdfs:subClassOf ex:MotorVehicle. ... – PowerPoint PPT presentation

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Title: Defining RDF Vocabularies: RDF Schema


1
Defining RDF Vocabularies RDF Schema
2
Introduction
  • RDF provides a way to express simple statements
    about resources, using named properties and
    values.
  • RDF user communities also need the ability to
    define the vocabularies (terms) they intend to
    use in those statements, specifically, to
    indicate that they are describing specific kinds
    or classes of resources, and will use specific
    properties in describing those resources.
  • extermsTent extermsmodel, extermsweightInKg,
    and extermspackedSize
  • ex2Book or ex2MagazineArticle ex2author,
    ex2title, ex2subject
  • ex3Person and ex3Company ex3age,
    ex3jobTitle, ex3stockSymbol, and
    ex3numberOfEmployees.

3
Introduction (Cont.)
  • RDF itself provides no means for defining such
    application-specific classes and properties.
  • Instead, such classes and properties are
    described as an RDF vocabulary, using extensions
    to RDF referred to as RDF Schema.
  • RDF Schema provides the facilities needed to
    describe classes and properties, and to indicate
    which classes and properties are expected to be
    used together
  • In other words, RDF Schema provides a type system
    for RDF

4
Introduction (Cont.)
  • Vocabulary descriptions (schemas) written in the
    RDF Schema language are legal RDF graphs.
  • RDF software that is not written to also process
    the additional RDF Schema vocabulary can still
    interpret a schema as a legal RDF graph
    consisting of various resources and properties,
    but will not "understand" the additional built-in
    meanings of the RDF Schema terms.
  • To understand these additional meanings, RDF
    software must be written to process an extended
    language that includes not only the rdf
    vocabulary, but also the rdfs vocabulary,
    together with their built-in meanings.

5
Describe Class
  • A class in RDF Schema corresponds to the generic
    concept of a Type or Category
  • Classes are described using the RDF Schema
    resources rdfsClass and rdfsResource, and the
    properties rdftype and rdfssubClassOf
  • In RDF Schema, a class is any resource having an
    rdftype property whose value is the resource
    rdfsClass

exMotorVehicle rdftype
rdfsClass exVan rdftype rdfsClass exTruck
rdftype rdfsClass
exthingscompanyCar rdftype exMotorVehicle
6
Describe Subclass
  • The specialization relationship between two
    classes is described using the predefined
    rdfssubClassOf property to relate the two
    classes
  • The rdfssubClassOf property is transitive
  • A class may be a subclass of more than one class
  • RDF Schema defines all classes as subclasses of
    class rdfsResource

exVan rdfssubClassOf exMotorVehicle
exVan rdfssubClassOf exMotorVehicle
exMiniVan rdfssubClassOf exVan
7
A Vehicle Class Hierarchy
8
A Vehicle Class Hierarchy (Cont.)
exMotorVehicle rdftype rdfsClass .
exPassengerVehicle rdftype rdfsClass .
exVan rdftype rdfsClass . exTruck
rdftype rdfsClass . exMiniVan rdftype
rdfsClass . exPassengerVehicle
rdfssubClassOf exMotorVehicle . exVan
rdfssubClassOf exMotorVehicle . exTruck
rdfssubClassOf exMotorVehicle . exMiniVan
rdfssubClassOf exVan . exMiniVan
rdfssubClassOf exPassengerVehicle .
ex13.xml
ex14.xml (Type Node Abbreviation)
ex15.xml (Instance)
9
Describe Properties
  • User communities also need to be able to describe
    specific properties that characterize those
    classes of things.
  • In RDF Schema, properties are described using the
    RDF class rdfProperty, and the RDF Schema
    properties rdfsdomain, rdfsrange, and
    rdfssubPropertyOf.
  • All properties in RDF are described as instances
    of class rdfProperty

extermsweightInKg rdftype rdfProperty
10
rdfsrange and rdfsdomain
  • RDF Schema also provides vocabulary for
    describing how properties and classes are
    intended to be used together in RDF data.
  • The most important information of this kind is
    supplied by using the RDF Schema properties
    rdfsrange and rdfsdomain
  • rdfsrange indicate that the values of a
    particular property are instances of a designated
    class
  • rdfsdomain indicate that a particular property
    applies to a designated class

11
rdfsrange and rdfsdomain (Example)
exPerson rdftype rdfsClass . exauthor
rdftype rdfProperty . exauthor
rdfsrange exPerson .
exage rdftype rdfProperty . exage
rdfsrange xsdinteger .
exBook rdftype rdfsClass . exauthor
rdftype rdfProperty . exauthor rdfsdomain
exBook .
ex16.xml
ex17.xml (instance)
12
Other Schema Information
  • rdfscomment property a human-readable
    description of a resource
  • rdfslabel property a more human-readable
    version of a resource's name
  • rdfsseeAlso a resource that might provide
    additional information about the subject
    resource.
  • rdfsisDefinedBy property a subproperty of
    rdfsseeAlso, and can be used to indicate a
    resource that "defines" the subject resource.

13
Richer Schema Languages
  • Richer schema capabilities that have been
    identified as useful (but that are not provided
    by RDF Schema) include
  • Cardinality constraints on properties, e.g., that
    a Person has exactly one biological father.
  • Specifying that a given property (such as
    exhasAncestor) is transitive, e.g., that if A
    exhasAncestor B, and B exhasAncestor C, then A
    exhasAncestor C.
  • Specifying that a given property is a unique
    identifier (or key) for instances of a particular
    class.
  • Specifying that two different classes (having
    different URIrefs) actually represent the same
    class.

14
Richer Schema Languages (Cont.)
  • Richer schema capabilities (Cont.)
  • Specifying that two different instances (having
    different URIrefs) actually represent the same
    individual.
  • Specifying constraints on the range or
    cardinality of a property that depend on the
    class of resource to which a property is applied,
    e.g., being able to say that for a soccer team
    the exhasPlayers property has 11 values, while
    for a basketball team the same property should
    have only 5 values.
  • The ability to describe new classes in terms of
    combinations (e.g., unions and intersections) of
    other classes, or to say that two classes are
    disjoint (i.e., that no resource is an instance
    of both classes).
  • DAMLOIL, OWL
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