rdf and owl

RDF & OWLA simple overview of the building blocks of

the Semantic WebPresented by Rachel Lovinger

Semantic Web Affinity Group

December 2007

Semantic Web Affinity Group – Dec 2007

RDF = Resource Description Framework


Purpose: To provide a structure (aka framework) for describing identified things (aka resources)

RDF


Identified?

In order to make meaningful statements in RDF, the thing you’re talking about has to be identified in some unique way.

http://www.foaf.com/Person#RachelLovingerhttp://www.allmovie.com/Actor#WillSmith

URIs (uniform resource identifiers) look like URLs, but they may not represent an actual web page.

RDF


Composed of three basic elements• Resources – the things being described• Properties – the relationships between things• Classes – the buckets used to group the things

RDF


The elements are combined to make simple statements in the form of Triples

<Subject> <Predicate> <Object>

Men In Black stars Will Smith

<MenInBlack> <hasStar> <WillSmith>

RDF


Information Expressed in Triples<http://www.w3.org/2001/sw/RDFCore/ntriples/> <dc:creator> "Dave Beckett" .<http://www.w3.org/2001/sw/RDFCore/ntriples/> <dc:creator> "Art Barstow" .<http://www.w3.org/2001/sw/RDFCore/ntriples/> <dc:publisher> <http://www.w3.org/> .

Can also be expressed as XML<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.w3.org/2001/sw/RDFCore/ntriples/"> <dc:creator>Art Barstow</dc:creator>

<dc:creator>Dave Beckett</dc:creator> <dc:publisher rdf:resource="http://www.w3.org/"/>

</rdf:Description> </rdf:RDF>

RDF


RDF Properties• type • subClassOf• subPropertyOf• range • domain• label• comment

RDF


type – a resource belongs to a certain class

<WillSmith> <type> <Actor>

This defines which properties will be relevant to Will Smith.

RDF


subClassOf – a class belongs to a parent class

<Actor> <subClassOf> <Person>

This means that all members of the actor class are also members of the Person class. All properties are inherited, and new properties specific to Actor can be added.

<WillSmith> <type> <Actor>implies <WillSmith> <type> <Person>

RDF


subPropertyOf – a property has a parent property

<hasStar> <subPropertyOf> <hasActor>

This means that, if you make a statement using the hasStar property, a more general statement using the hasActor property is also true.

<MenInBlack> <hasStar> <WillSmith>implies <MenInBlack> <hasActor> <WillSmith>

RDF


range & domain – the types of resources that use a property

<hasStar> <range> <Actor><hasStar> <domain> <Movie>

This means that, if you make a statement using the hasStar property, the system will assume that the subject is a Movie and the object is an Actor.

<WillSmith> <hasStar> <MenInBlack>

is an untrue statement, but not invalid

RDF


label – a human-readable name for a resource

<http://www.allmovie.com/Actor#WillSmith> <label> <Will Smith>

RDF


comment – a human-readable description

<https://aarfwiki.main.corp/wiki/index.php/File:RDF_OWL.pdf> <comment> <A presentation that Rachel gave at the December 2007 Semantic Web Affinity Group Meeting>

RDF


RDF

Blackberry

Fruit

typeOfBerryPie

EdibleThing

typeOf

subClassOf

ingredientOf

Blackberry


Why is RDF uniquely suited to expressing data and data relationships?• More flexible – data relationships can be explored from all angles• More efficient – large scale, data can be read more quickly

– not linear like a traditional database– not hierarchical like XML

RDF


Namespaces


A method for qualifying names used in an XML document. Can be used to indicate usage of a standard, or to specify a unique version of the term.• dc:creator• rdf:type• foaf:Person• foaf:knows• aarf:Employee

Namespaces


OWL = Web Ontology Language


OWL


Purpose: To develop ontologies that are compatible with the World Wide Web.

OWL


Ontologies?

Definition and classification of concepts and entities, and the relationships between them.

OWL


Based on the basic elements of RDF; adds more vocabulary for describing properties and classes.

• Relationships between classes (ex: disjointWith)• Equality (ex: sameAs)• Richer properties (ex: symmetrical)• Class property restrictions (ex: allValuesFrom)

OWL


Relationships between Classes• disjointWith – resources belonging to one class

cannot belong to the other<Person> <disjointWith> <Country>

• complementOf – the members of one class are all the resources that do not belong to the other <InanimateThings> <complementOf> <LivingThings>

OWL


Equality• sameAs – indicates that two resources actually

refer to the same real-world thing or concept<wills> <sameAs> <wismith>

• equivalentClass – indicates that two classes have the same set of members<CoopBoardMembers> <equivalentClass> <CoopResidents>

OWL


Richer Properties• Symmetric – a relationship between A and B is

also true between B and A<WillSmith> <marriedTo> <JadaPinkettSmith>implies <JadaPinkettSmith> <marriedTo> <WillSmith>

• Transitive – a relationship between A and B and between B and C is also true between A and C<piston> <isPartOf> <engine><engine> <isPartOf> <automobile>implies <piston> <isPartOf> <automobile>

OWL


Richer Properties continued• inverseOf – a relationship of type X between A

and B implies a relationship of type Y between B and A<starsIn> <inverseOf> <hasStar><MenInBlack> <hasStar> <WillSmith>implies <WillSmith> <starsIn> <MenInBlack>

OWL


Class Property Restrictions – define the members of a class based on their properties

• allValuesFrom – resources with properties that only have values that meet this criteria– Example: Property: hasParents, allValuesFrom: Human – Resources that meet this criteria can be defined as also being

members of the Human class

• someValuesFrom – resources with properties that have at least one value that meets criteria– Example: Property: hasGraduated, someValuesFrom: College – Resources that meet this criteria can be defined as being

members of the CollegeGraduates class

OWL


This seems complicated. Why do it?

These capabilities allows systems to express and make sense of first order logic.• All men are mortal • Socrates is a man • Therefore, Socrates is mortal

OWL


Inferences• Create new triples based on existing triples• Deduce new facts based on the stated facts

<piston> <isPartOf> <engine><engine> <isPartOf> <automobile>implies <piston> <isPartOf> <automobile>

OWL


Three Flavors of OWL• OWL Lite – uses a subset of the capabilities• OWL DL – uses all the capabilities, but some

are used in restricted ways• OWL Full – unrestricted use of capabilities; no

guarantee that all resulting statements are valid

OWL


SKOS = Simple Knowledge Organization System


• Also based on RDF• Designed specifically to express information

that’s more hierarchical – broader terms, narrower terms, preferred terms and other thesaurus-like relationships

• Extendable into OWL, if needed

SKOS


Need more?


• SchemaWeb: http://www.schemaweb.info/default.aspx • RDF Primer: http://www.w3.org/TR/REC-rdf-syntax/ • OWL / Semantic Web: http://www.w3.org/2004/OWL/ • SKOS: http://www.w3.org/2004/02/skos/ • Dublin Core: http://dublincore.org/ • Namespaces: http://www.w3.org/TR/REC-xml-names/• URIs: http://www.w3.org/Addressing/

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