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RDF and XML

Explore the potential of RDF, XML, and DAML+OIL in improving search engine accuracy and resource sharing on the Semantic Web. Learn the concepts behind RDF, semantic modeling, and limitations of XML for semantic markup. Discover how RDF Schema defines vocabularies and see examples of RDF syntax in XML documents.

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RDF and XML

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  1. RDF and XML

  2. Lecture Overview • Semantic Web • XML • RDF • DAML + OIL ( Time permitting)

  3. Problems with current search engines • Current search engines = keywords: • high recall, low precision • sensitive to vocabulary • insensitive to implicit content

  4. Search engines on theSemantic Web • concept search instead of keyword search • semantic narrowing/widening of queries • query-answering over >1 document • document transformation operators

  5. So what is the Semantic Web? • XML • RDF • RDF Schema • DAML+OIL (OWL)

  6. XML: User definable and domain specific markup HTML: <H1>Introduction to AI</H1><UL> <LI>Teacher: Frank van Harmelen<LI>Students: 1AI, 1I<LI>Requirements: none</UL> XML: <course><title>Introduction to AI</title><teacher>Frank van Harmelen</teacher><students>1AI, 1I</students><req>none</req></course>

  7. XML: document = labelled tree course title teacher students name http • node = label + attr/values + contents <course date=“...”><title>...</title><teacher>...</teacher> <name>...</name> <http>...</http><students>...</students></course> = • XML Schema: grammars for describing legal trees and datatypes • So:why not use XML to represent semantics?

  8. Syntax versus Semantics • Syntax: the structure of your data • Semantics: the meaning of your data • Two conditions necessary for interoperability: • Adopt a common syntax: this enables applications to parse the data. • Adopt a means for understanding the semantics: this enables applications to use the data.

  9. XML and Semantics? <Predator> … </Predator> • Predator: a medium-altitude, long-endurance unmanned aerial vehicle system. • Predator : one that victimizes, plunders, or destroys, especially for one's own gain. • Predator : an organism that lives by preying on other organisms. • Predator: a company which specializes in camouflage attire.

  10. XML: limitations for semantic markup • XML makes no commitment on:  Domain-specific ontological vocabulary  Ontological modeling primitives • Requires pre-arranged agreement on  &  • Only feasible for closed collaboration • agents in a small & stable community • pages on a small & stable intranet • Not suited for sharing Web-resources

  11. What is RDF ? • RDF is a data model • the model is domain-neutral, application-neutral and an ISO standard. • the model can be viewed as directed, labeled graphs or as an object-oriented model (object/attribute/value) • RDF data model is an abstract, conceptual layer independent of XML • consequently, XML is a transfer syntax for RDF, not a component of RDF • RDF data might never occur in XML form

  12. value resource property http://www.w3.org/TR/REC-rdf-syntax/ author “Ora Lassila” RDF model • RDF “statements” consist of resources (= nodes)which have propertieswhich have values (= nodes,strings) = subject= predicate= object “http://www.w3.org/TR/REC-rdf-syntax/ has the author Ora Lassila”

  13. RDF Model Example “W3C” dc:Publisher http://www.w3.org/TR/REC-rdf-syntax/ dc:Creator dc:Date “Ora Lassila” “1999-02-22”

  14. RDF Schema • Defines small vocabulary for RDF: • Class, subClassOf, type • Property, subPropertyOf • domain, range • Vocabulary can be used to define other vocabularies for your application domain Person subClassOf subClassOf range domain Student Researcher hasSuperVisor type type Frank Jeen hasSuperVisor

  15. RDF Schema syntax in XML <rdf:Description ID="MotorVehicle"> <rdf:type resource="http://www.w3.org/...#Class"/> <rdfs:subClassOf rdf:resource="http://www.w3.org/...#Resource"/> </rdf:Description> <rdf:Description ID="Truck"> <rdf:type resource="http://www.w3.org/...#Class"/> <rdfs:subClassOf rdf:resource="#MotorVehicle"/> </rdf:Description> <rdf:Description ID="registeredTo"> <rdf:type resource="http://www.w3.org/...#Property"/> <rdfs:domain rdf:resource="#MotorVehicle"/> <rdfs:range rdf:resource="#Person"/> </rdf:Description> <rdf:Description ID=”ownedBy"> <rdf:type resource="http://www.w3.org/...#Property"/> <rdfs:subPropertyOf rdf:resource="#registeredTo"/> </rdf:Description>

  16. Conclusions about RDF(S) ? • Next step up from plain XML • (small) ontological commitment to modeling primitives • possible to define vocabulary • However: • no precisely described meaning • no inference model

  17. Beyond RDF: OIL & DAML • OIL extends RDF Schema to a fully-fledged knowledge representation language. • logical expressions • data-typing • cardinality • quantifiers • http://www.ontoknowledge.org • DAML = US sister of OIL • Merged as DAML+OIL in 2001 • Becomes OWL W3C standard in March '03

  18. DAML+OIL (by example) class-def animal % animals are a class class-def plant % plants are a class subclass-of NOT animal% that is disjoint from animals class-def tree subclass-of plant % trees are a type of plants class-def branch slot-constraint is-part-of % branches are parts of some tree has-valuetree max-cardinality 1 class-def defined carnivore % carnivores are animals subclass-of animal slot-constraint eats % that eat any other animals value-typeanimal class-def defined herbivore % herbivores are animals subclass-of animal, NOT carnivore % that are not carnivores, and slot-constraint eats % they eat plants or parts of plants value-type plant OR (slot-constraint is-part-of has-value plant)

  19. DAML+OIL as RDFS extension RDF(S) DAML+OIL • class-def • subclass-of • slot-def • subslot-of • domain • range • class-expressions • AND, OR, NOT • slot-constraints • has-value, value-type • cardinality • slot-properties • trans, symm

  20. DAML+OIL: Classes  ! <daml:Class rdf:ID="Male"> <rdfs:subClassOf rdf:resource="#Animal"/> </daml:Class> <daml:Class rdf:ID="Female"> <rdfs:subClassOf rdf:resource="#Animal"/> <daml:disjointWith rdf:resource="#Male"/> </daml:Class> <daml:Class rdf:ID="Man"> <rdfs:subClassOf rdf:resource="#Person"/> <rdfs:subClassOf rdf:resource="#Male"/> </daml:Class>

  21. Class-Building Operations • Relation to other Classes • rdfs:subClassOf • daml:disjointWith • daml:disjointUnionOf • daml:sameClassAs • daml:equivalentTo • Contained Elements: • daml:oneOf • Boolean combinations: • daml:intersectionOf • daml:unionOf • daml:complementOf

  22. DAML+OIL: Properties <daml:ObjectProperty rdf:ID="hasParent"> <rdfs:domain rdf:resource="#Animal"/> <rdfs:range rdf:resource="#Animal"/> </daml:ObjectProperty> <daml:ObjectProperty rdf:ID="hasChild"> <daml:inverseOf rdf:resource="#hasParent"/> </daml:ObjectProperty> <daml:UniqueProperty rdf:ID="hasMother"> <rdfs:subPropertyOf rdf:resource="#hasParent"/> <rdfs:range rdf:resource="#Female"/> </daml:UniqueProperty>

  23. Property-Building Operations • Basic Types • daml:ObjectProperty • daml:DataTypeProperty • Special Types • daml:TransitiveProperty • daml:UniqueProperty • daml:UnambigousProperty • Further Restrictions • rdfs:subPropertyOf • rdfs:domain • rdfs:range • daml:samePropertyAs • daml:inverseOf

  24. DAML+OIL:Property Restrictions <daml:Class rdf:ID="Person"> <rdfs:subClassOf rdf:resource="#Animal"/> <rdfs:subClassOf> <daml:Restriction> <daml:onProperty rdf:resource="#hasFather"/> <daml:toClass rdf:resource="#Man"/> </daml:Restriction> <daml:Restriction daml:cardinality="1"> <daml:onProperty rdf:resource="#hasFather"/> </daml:Restriction> </rdfs:subClassOf> </daml:Class>

  25. DAML+OIL:Property Restrictions <daml:Class rdf:ID="Person"> <rdfs:subClassOf rdf:resource="#Animal"/> <rdfs:subClassOf> <daml:Restriction daml:cardinalityQ="1"> <daml:onProperty rdf:resource="#hasFather"/> <daml:hasClassQ rdf:resource="#Man"/> </daml:Restriction> </rdfs:subClassOf> </daml:Class>

  26. Restrictions • General • daml:Restriction • daml:onProperty • Number Restrictions • daml:cardinality • daml:maxCardinality • daml:minCardinality • Value and Type Restrictions • daml:toClass • daml:hasValue • daml:hasClass • Combinations • daml:cardinalityQ • daml:maxCardinalityQ • daml:minCardinalityQ

  27. Resources • homepages.cwi.nl/~lynda/spool/sw-tue-2003.ppt • www.daml.org/meetings/2003/05/SWMU/briefings/ 07_1045_Essential_Building_Blocks.ppt • www.ltg.ed.ac.uk/~ht/ora-rdf-dagstuhl.ppt

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