1. RDF and XML tutorial

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

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

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

5. 5 So what is the Semantic Web? The “Semantic Web Wedding Cake” Crash course l XML l RDF l RDF Schema l DAML+OIL (OWL)

6. 6 TBL talk at XML 2000

7. 7 XML: User definable and domain specific markup Introduction to AI Teacher: Frank van Harmelen Students: 1AI, 1I Requirements: none HTML: Introduction to AI Frank van Harmelen 1AI, 1I none XML :

8. 8 XML: document = labelled tree course teachertitlestudents namehttp............... = XML Schema: grammars for describing legal trees and datatypes node = label + attr/values + contents So: why not use XML to represent semantics?

9. 9 Syntax versus Semantics Syntax: the structure of your data Semantics: the meaning of your data Two conditions necessary for interoperability: l Adopt a common syntax: this enables applications to parse the data. l Adopt a means for understanding the semantics: this enables applications to use the data.

10. 10 XML and Semantics? … 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.

11. 11 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 l agents in a small & stable community l pages on a small & stable intranet Not suited for sharing Web-resources

12. 12 What is RDF ? RDF is a data model the model is domain-neutral, application-neutral and ready for internationalization (i18n) 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

13. 13 RDF model RDF “statements” consist of resources (= nodes) which have properties which have values (= nodes,strings) http://www.w3.org/TR/REC-rdf-syntax/ “Ora Lassila” author = subject = predicate = object “http://www.w3.org/TR/REC-rdf-syntax/ has the author Ora Lassila” resource value property

14. 14 RDF Model Example http://www.w3.org/TR/REC-rdf-syntax/ “Ora Lassila” dc:Creator “1999-02-22” dc:Date “W3C” dc:Publisher

15. 15 Complex values So far, values of properties have been strings A graph node (corresponding to a resource) also can be the value of a property l arbitrarily complex tree and graph structures are possible l syntactically, values can be embedded (i.e. lexically in-line) or referenced (linked) Example: http://www.w3.org/TR/REC-rdf-syntax/ “Ora Lassila” dc:Creator “ora.lassila@nokia.com” p:EMail p:Name

16. 16 Complex values (continued) Corresponding triples { “http://www.w3.org/TR/PR-rdf-syntax/”, dc:Creator, x } { x, p:Name, “Ora Lassila” } { x, p:EMail, “ora.lassila@nokia.com” } http://www.w3.org/TR/REC-rdf-syntax/ “Ora Lassila” dc:Creator “ora.lassila@nokia.com” p:EMail p:Name

17. 17 Containers Containers are collections l they allow grouping of resources (or literal values) It is possible to make statements about the container (as a whole) or about its members individually Different types of containers exist l bag - unordered collection l seq - ordered collection (= “sequence”) l alt - represents alternatives It is also possible to create collections based on URI patterns l for example, all files in a particular web site Duplicate values are permitted l there is no mechanism to enforce unique value constraints

18. 18 Containers (continued) http://www.w3.org/TR/REC-rdf-syntax “Ora Lassila” rdf:_1 rdf:Seq dc:Creator rdf:Type “Ralph Swick” rdf:_2

19. 19 Higher-order statements One can make RDF statements about other RDF statements l example: “Ralph believes that the web contains one billion documents” Higher-order statements l allow us to express beliefs (and other modalities) l are important for trust models, digital signatures,etc. l also: metadata about metadata l are represented by modeling RDF in RDF itself

20. 20 Reification RDF is not really second-order But it does provide a built-in predicate vocabulary for reification http://www.w3.org/TR/REC-rdf-syntax“Ora Lassila” dc:Creator “Library of Congress” dc:Creator The dotted box corresponds to the following statements { x, rdf:predicate, “dc:creator” } { x, rdf:subject, “http://www.w3.org/TR/RED-rdf-syntax } { x, rdf:object, “Ora Lassila” } { x, rdf:type, “rdf:statement” }

21. 21 Reification pers05 ISBN... Author-of NYT claims ISBN... Any statement can be an object graphs can be nested - reification

22. 22 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 StudentResearcher subClassOf Jeen type hasSuperVisor domain range Frank type hasSuperVisor

23. 23 RDF Schema syntax in XML

24. 24 Conclusions about RDF(S) Next step up from plain XML l (small) ontological commitment to modeling primitives l possible to define vocabulary However: l no precisely described meaning l no inference model ?

25. 25 Beyond RDF: OIL & DAML OIL extends RDF Schema to a fully-fledged knowledge representation language. l logical expressions l data-typing l cardinality l quantifiers l http://www.ontoknowledge.org DAML = US sister of OIL Merged as DAML+OIL in 2001 Becomes OWL W3C standard in March '03

26. 26 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-value tree max-cardinality 1 class-def defined carnivore% carnivores are animals subclass-of animal slot-constraint eats % that eat any other animals value-type animal 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)

27. 27 DAML+OIL as RDF(S) extension <rdf:type rdf:resource=” http://www.ontoknowledge.org /#DefinedClass”/>

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

29. 29 DAML+OIL: Classes  !

30. 30 Class-Building Operations Relation to other Classes l rdfs:subClassOf l daml:disjointWith l daml:disjointUnionOf l daml:sameClassAs l daml:equivalentTo Contained Elements: daml:oneOf Boolean combinations: l daml:intersectionOf l daml:unionOf l daml:complementOf

31. 31 DAML+OIL: Properties

32. 32 Property-Building Operations Basic Types l daml:ObjectProperty l daml:DataTypeProperty Special Types l daml:TransitiveProperty l daml:UniqueProperty l daml:UnambigousProperty Further Restrictions l rdfs:subPropertyOf l rdfs:domain l rdfs:range l daml:samePropertyAs l daml:inverseOf

33. 33 DAML+OIL: Property Restrictions

34. 34 DAML+OIL: Property Restrictions

35. 35 Restrictions General l daml:Restriction l daml:onProperty Number Restrictions l daml:cardinality l daml:maxCardinality l daml:minCardinality Combinations l daml:cardinalityQ l daml:maxCardinalityQ l daml:minCardinalityQ Value and Type Restrictions l daml:toClass l daml:hasValue l daml:hasClass

36. 36 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