RDF and OWL
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RDF and OWL

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A simple overview of the building blocks of the Semantic Web. I created this to present to the Semantic Web Affinity Group at Razorfish.

A simple overview of the building blocks of the Semantic Web. I created this to present to the Semantic Web Affinity Group at Razorfish.

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RDF and OWL RDF and OWL Presentation Transcript

  • RDF & OWL A simple overview of the b uilding blocks of the Semantic Web Presented by Rachel Lovinger Semantic Web Affinity Group December 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#RachelLovinger
    • http://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> &quot;Dave Beckett&quot; .
    • <http://www.w3.org/2001/sw/RDFCore/ntriples/> <dc:creator> &quot;Art Barstow&quot; .
    • <http://www.w3.org/2001/sw/RDFCore/ntriples/> <dc:publisher> <http://www.w3.org/> .
    • Can also be expressed as XML
    • <rdf:RDF xmlns:rdf=&quot;http://www.w3.org/1999/02/22-rdf-syntax-ns#&quot; xmlns:dc=&quot;http://purl.org/dc/elements/1.1/&quot;>
    • <rdf:Description rdf:about=&quot;http://www.w3.org/2001/sw/RDFCore/ntriples/&quot;> <dc:creator>Art Barstow</dc:creator>
    • <dc:creator>Dave Beckett</dc:creator>
    • <dc:publisher rdf:resource=&quot;http://www.w3.org/&quot;/>
    • </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 typeOf BerryPie 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/
    Resources