Post on 15-Jan-2015
description
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
Semantic Web Affinity Group – Dec 2007
Purpose: To provide a structure (aka framework) for describing identified things (aka resources)
RDF
Semantic Web Affinity Group – Dec 2007
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
Semantic Web Affinity Group – Dec 2007
Composed of three basic elements• Resources – the things being described• Properties – the relationships between things• Classes – the buckets used to group the things
RDF
Semantic Web Affinity Group – Dec 2007
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
Semantic Web Affinity Group – Dec 2007
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
Semantic Web Affinity Group – Dec 2007
RDF Properties• type • subClassOf• subPropertyOf• range • domain• label• comment
RDF
Semantic Web Affinity Group – Dec 2007
type – a resource belongs to a certain class
<WillSmith> <type> <Actor>
This defines which properties will be relevant to Will Smith.
RDF
Semantic Web Affinity Group – Dec 2007
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
Semantic Web Affinity Group – Dec 2007
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
Semantic Web Affinity Group – Dec 2007
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
Semantic Web Affinity Group – Dec 2007
label – a human-readable name for a resource
<http://www.allmovie.com/Actor#WillSmith> <label> <Will Smith>
RDF
Semantic Web Affinity Group – Dec 2007
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
Semantic Web Affinity Group – Dec 2007
RDF
Blackberry
Fruit
typeOfBerryPie
EdibleThing
typeOf
subClassOf
ingredientOf
Blackberry
Semantic Web Affinity Group – Dec 2007
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
Semantic Web Affinity Group – Dec 2007
Namespaces
Semantic Web Affinity Group – Dec 2007
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
Semantic Web Affinity Group – Dec 2007
OWL = Web Ontology Language
Semantic Web Affinity Group – Dec 2007
OWL
Semantic Web Affinity Group – Dec 2007
Purpose: To develop ontologies that are compatible with the World Wide Web.
OWL
Semantic Web Affinity Group – Dec 2007
Ontologies?
Definition and classification of concepts and entities, and the relationships between them.
OWL
Semantic Web Affinity Group – Dec 2007
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
Semantic Web Affinity Group – Dec 2007
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
Semantic Web Affinity Group – Dec 2007
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
Semantic Web Affinity Group – Dec 2007
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
Semantic Web Affinity Group – Dec 2007
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
Semantic Web Affinity Group – Dec 2007
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
Semantic Web Affinity Group – Dec 2007
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
Semantic Web Affinity Group – Dec 2007
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
Semantic Web Affinity Group – Dec 2007
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
Semantic Web Affinity Group – Dec 2007
SKOS = Simple Knowledge Organization System
Semantic Web Affinity Group – Dec 2007
• 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
Semantic Web Affinity Group – Dec 2007
Need more?
Semantic Web Affinity Group – Dec 2007
• 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/
Resources