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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.

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RDF and OWL

  1. 1. RDF & OWL A simple overview of the b uilding blocks of the Semantic Web Presented by Rachel Lovinger Semantic Web Affinity Group December 2007
  2. 2. RDF = Resource Description Framework
  3. 3. <ul><li>Purpose: To provide a structure (aka framework) for describing identified things (aka resources) </li></ul>RDF
  4. 4. <ul><li>Identified ? </li></ul><ul><li>In order to make meaningful statements in RDF, the thing you’re talking about has to be identified in some unique way. </li></ul><ul><li>http://www.foaf.com/Person#RachelLovinger </li></ul><ul><li>http://www.allmovie.com/Actor#WillSmith </li></ul><ul><li>URIs (uniform resource identifiers) look like URLs, but they may not represent an actual web page. </li></ul>RDF
  5. 5. <ul><li>Composed of three basic elements </li></ul><ul><li>Resources – the things being described </li></ul><ul><li>Properties – the relationships between things </li></ul><ul><li>Classes – the buckets used to group the things </li></ul>RDF
  6. 6. <ul><li>The elements are combined to make simple statements in the form of Triples </li></ul><ul><li><Subject> <Predicate> <Object> </li></ul><ul><li>Men In Black stars Will Smith </li></ul><ul><li><MenInBlack> <hasStar> <WillSmith> </li></ul>RDF
  7. 7. <ul><li>Information Expressed in Triples </li></ul><ul><li><http://www.w3.org/2001/sw/RDFCore/ntriples/> <dc:creator> &quot;Dave Beckett&quot; . </li></ul><ul><li><http://www.w3.org/2001/sw/RDFCore/ntriples/> <dc:creator> &quot;Art Barstow&quot; . </li></ul><ul><li><http://www.w3.org/2001/sw/RDFCore/ntriples/> <dc:publisher> <http://www.w3.org/> . </li></ul><ul><li>Can also be expressed as XML </li></ul><ul><li><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;> </li></ul><ul><li><rdf:Description rdf:about=&quot;http://www.w3.org/2001/sw/RDFCore/ntriples/&quot;> <dc:creator>Art Barstow</dc:creator> </li></ul><ul><li><dc:creator>Dave Beckett</dc:creator> </li></ul><ul><li><dc:publisher rdf:resource=&quot;http://www.w3.org/&quot;/> </li></ul><ul><li></rdf:Description> </li></ul><ul><li></rdf:RDF> </li></ul>RDF
  8. 8. <ul><li>RDF Properties </li></ul><ul><li>type </li></ul><ul><li>subClassOf </li></ul><ul><li>subPropertyOf </li></ul><ul><li>range </li></ul><ul><li>domain </li></ul><ul><li>label </li></ul><ul><li>comment </li></ul>RDF
  9. 9. <ul><li>type – a resource belongs to a certain class </li></ul><ul><li><WillSmith> <type> <Actor> </li></ul><ul><li>This defines which properties will be relevant to Will Smith. </li></ul>RDF
  10. 10. <ul><li>subClassOf – a class belongs to a parent class </li></ul><ul><li><Actor> <subClassOf> <Person> </li></ul><ul><li>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. </li></ul><ul><li><WillSmith> <type> <Actor> </li></ul><ul><li>implies <WillSmith> <type> <Person> </li></ul>RDF
  11. 11. <ul><li>subPropertyOf – a property has a parent property </li></ul><ul><li><hasStar> <subPropertyOf> <hasActor> </li></ul><ul><li>This means that, if you make a statement using the hasStar property, a more general statement using the hasActor property is also true. </li></ul><ul><li><MenInBlack> <hasStar> <WillSmith> </li></ul><ul><li>implies <MenInBlack> <hasActor> <WillSmith> </li></ul>RDF
  12. 12. <ul><li>range & domain – the types of resources that use a property </li></ul><ul><li><hasStar> <range> <Actor> </li></ul><ul><li><hasStar> <domain> <Movie> </li></ul><ul><li>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. </li></ul><ul><li><WillSmith> <hasStar> <MenInBlack> </li></ul><ul><li>is an untrue statement, but not invalid </li></ul>RDF
  13. 13. <ul><li>label – a human-readable name for a resource </li></ul><ul><li><http://www.allmovie.com/Actor#WillSmith> <label> <Will Smith> </li></ul>RDF
  14. 14. <ul><li>comment – a human-readable description </li></ul><ul><li><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> </li></ul>RDF
  15. 15. RDF Blackberry Fruit typeOf BerryPie EdibleThing typeOf subClassOf ingredientOf Blackberry
  16. 16. <ul><li>Why is RDF uniquely suited to expressing data and data relationships? </li></ul><ul><li>More flexible – data relationships can be explored from all angles </li></ul><ul><li>More efficient – large scale, data can be read more quickly </li></ul><ul><ul><li>not linear like a traditional database </li></ul></ul><ul><ul><li>not hierarchical like XML </li></ul></ul>RDF
  17. 17. Namespaces
  18. 18. <ul><li>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. </li></ul><ul><li>dc:creator </li></ul><ul><li>rdf:type </li></ul><ul><li>foaf:Person </li></ul><ul><li>foaf:knows </li></ul><ul><li>aarf:Employee </li></ul>Namespaces
  19. 19. OWL = Web Ontology Language
  20. 20. OWL
  21. 21. <ul><li>Purpose: To develop ontologies that are compatible with the World Wide Web. </li></ul>OWL
  22. 22. <ul><li>Ontologies ? </li></ul><ul><li>Definition and classification of concepts and entities, and the relationships between them. </li></ul>OWL
  23. 23. <ul><li>Based on the basic elements of RDF; adds more vocabulary for describing properties and classes. </li></ul><ul><li>Relationships between classes (ex: disjointWith) </li></ul><ul><li>Equality (ex: sameAs) </li></ul><ul><li>Richer properties (ex: symmetrical) </li></ul><ul><li>Class property restrictions (ex: allValuesFrom) </li></ul>OWL
  24. 24. <ul><li>Relationships between Classes </li></ul><ul><li>disjointWith – resources belonging to one class cannot belong to the other </li></ul><ul><li><Person> <disjointWith> <Country> </li></ul><ul><li>complementOf – the members of one class are all the resources that do not belong to the other </li></ul><ul><li><InanimateThings> <complementOf> <LivingThings> </li></ul>OWL
  25. 25. <ul><li>Equality </li></ul><ul><li>sameAs – indicates that two resources actually refer to the same real-world thing or concept </li></ul><ul><li><wills> <sameAs> <wismith> </li></ul><ul><li>equivalentClass – indicates that two classes have the same set of members </li></ul><ul><li><CoopBoardMembers> <equivalentClass> <CoopResidents> </li></ul>OWL
  26. 26. <ul><li>Richer Properties </li></ul><ul><li>Symmetric – a relationship between A and B is also true between B and A </li></ul><ul><li><WillSmith> <marriedTo> <JadaPinkettSmith> </li></ul><ul><li>implies <JadaPinkettSmith> <marriedTo> <WillSmith> </li></ul><ul><li>Transitive – a relationship between A and B and between B and C is also true between A and C </li></ul><ul><li><piston> <isPartOf> <engine> </li></ul><ul><li><engine> <isPartOf> <automobile> </li></ul><ul><li>implies <piston> <isPartOf> <automobile> </li></ul>OWL
  27. 27. <ul><li>Richer Properties continued </li></ul><ul><li>inverseOf – a relationship of type X between A and B implies a relationship of type Y between B and A </li></ul><ul><li><starsIn> <inverseOf> <hasStar> </li></ul><ul><li><MenInBlack> <hasStar> <WillSmith> </li></ul><ul><li>implies <WillSmith> <starsIn> <MenInBlack> </li></ul>OWL
  28. 28. <ul><li>Class Property Restrictions – define the members of a class based on their properties </li></ul><ul><li>allValuesFrom – resources with properties that only have values that meet this criteria </li></ul><ul><ul><li>Example: Property: hasParents, allValuesFrom: Human </li></ul></ul><ul><ul><li>Resources that meet this criteria can be defined as also being members of the Human class </li></ul></ul><ul><li>someValuesFrom – resources with properties that have at least one value that meets criteria </li></ul><ul><ul><li>Example: Property: hasGraduated, someValuesFrom: College </li></ul></ul><ul><ul><li>Resources that meet this criteria can be defined as being members of the CollegeGraduates class </li></ul></ul>OWL
  29. 29. <ul><li>This seems complicated. Why do it? </li></ul><ul><li>These capabilities allows systems to express and make sense of first order logic. </li></ul><ul><li>All men are mortal </li></ul><ul><li>Socrates is a man </li></ul><ul><li>Therefore, Socrates is mortal </li></ul>OWL
  30. 30. <ul><li>Inferences </li></ul><ul><li>Create new triples based on existing triples </li></ul><ul><li>Deduce new facts based on the stated facts </li></ul><ul><li><piston> <isPartOf> <engine> </li></ul><ul><li><engine> <isPartOf> <automobile> </li></ul><ul><li>implies <piston> <isPartOf> <automobile> </li></ul>OWL
  31. 31. <ul><li>Three Flavors of OWL </li></ul><ul><li>OWL Lite – uses a subset of the capabilities </li></ul><ul><li>OWL DL – uses all the capabilities, but some are used in restricted ways </li></ul><ul><li>OWL Full – unrestricted use of capabilities; no guarantee that all resulting statements are valid </li></ul>OWL
  32. 32. SKOS = Simple Knowledge Organization System
  33. 33. <ul><li>Also based on RDF </li></ul><ul><li>Designed specifically to express information that’s more hierarchical – broader terms, narrower terms, preferred terms and other thesaurus-like relationships </li></ul><ul><li>Extendable into OWL, if needed </li></ul>SKOS
  34. 34. Need more?
  35. 35. <ul><li>SchemaWeb: http://www.schemaweb.info/default.aspx </li></ul><ul><li>RDF Primer: http://www.w3.org/TR/REC-rdf-syntax/ </li></ul><ul><li>OWL / Semantic Web: http://www.w3.org/2004/OWL/ </li></ul><ul><li>SKOS: http://www.w3.org/2004/02/skos/ </li></ul><ul><li>Dublin Core: http://dublincore.org/ </li></ul><ul><li>Namespaces: http://www.w3.org/TR/REC-xml-names/ </li></ul><ul><li>URIs: http://www.w3.org/Addressing/ </li></ul>Resources

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