Resource Description Framework Building the Semantic Web

1. Resource Description FrameworkBuilding the Semantic Web CS 502 – 20030226 Carl Lagoze – Cornell University Acknowledgements: Eric Miller Dieter Fensel

2. Illustration is a type of contribution M. Doeillustrated the book “Best Stories” Mary Doeanimated the cartoon “Best Stories – the movie” Cartoons and Books are types of Works animation is a type of contribution M. Doe and Mary Doe are pseudonyms for Susan Mann Show me the works to which Susan Mann contributed? Motivating the “Semantic Web”

3. Components of the Semantic Web

4. Modeling & Encoding Metadata Components: RDF • RDF (Resource Description Format) • The instantiation of the Warwick Framework on the Web • Support for and integration of multiple independent metadata vocabularies • Provides enabling technology for richly-structured metadata • Rich data model supporting notions of distinct entities and properties • Formal model with basis in logic • Primitives permit semantic inferencing • Expressible in machine readable manner (e.g., XML)

5. RDF Components • Formal data model • Syntax for interchange of data • Schema Type system (schema model) • Syntax for machine-understandable schemas • Query and profile protocols • Ontologies layered on top

6. RDF Data Model • Provides underlying structural foundation for the expression of application (instance) data models • for consistent encoding, exchange and processing of metadata • Provides for a basis for interoperability • Individual communities can then define and express semantics on the basic model • Model is distinct from the syntax for expressing it (1-to-many relationship)

7. RDF Data Model • Directed labeled graphs • Model elements • Resource • Property • Value • Statement • Containers

8. Resource Statement RDF Model Primitives Resource Property Value

9. Simple Example Resource Author “Eric”

10. RDF Syntax • RDF Model defines a formal relationships among resources, properties and values • Syntax is required to... • Store instances of the model into files • Communicate files from one application to another • XML is one well-supported syntax • There are syntax alternatives • Relational databases • Triple Stores

11. dc: dc: RDF Model Example #1 URI:R Title “CIMI Presentation” Creator “Eric Miller”

12. dc: dc: RDF Syntax Example #1 URI:R Title “CIMI Presentation” Creator “Eric Miller” <RDF xmlns = “http://www.w3.org/TR/WD-rdf-syntax#” xmlns:dc = “http://purl.org/dc/elements/1.0/”> <Description about = “URI:R”> <dc:Title> CIMI Presentation </dc:Title> <dc:Creator> Eric Miller </dc:Creator> </Description> </RDF>

13. dc: oa: URI:ERIC bib:Aff bib:Email bib:Name URI:OCLC “OCLC” “emiller@ oclc.org” “Eric Miller” RDF Model Example #2 URI:R Title “CIMI Presentation” Creator “Eric Miller”

14. RDF Syntax Example #2 <RDF xmlns = “http://www.w3.org/TR/WD-rdf-syntax#” xmlns:dc = “http://purl.org/dc/elements/1.0/” xmlns:bib = “http://www.bib.org/persons#” xmlns:oa = “http://www.agents.org/ag”> <Description about = “URI:R”> <dc:Title> CIMI Presentation </dc:Title> <oa:Creator> <Description> <bib:Name> Eric Miller </bib:Name> <bib:Email> emiller@oclc.org </bib:Email> <bib:Aff resource = “http://www.oclc.org” /> </Description> </oa:Creator> </Description> </RDF>

15. dc: admin:By dc: “LOC” URI:ERIC admin:On “03-09-99” admin:For bib:Aff bib:Email bib:Name “...” URI:OCLC “OCLC” “emiller@ oclc.org” “Eric Miller” RDF Model Example #3Reification URI:R Title “CIMI Presentation” Creator “Eric Miller”

16. RDF Containers • Permit the aggregation of several values for a property • Express multiple aggregation semantics • unordered • sequential or priority order • alternative

17. RDF Containers • Permit the aggregation of several values for a property • Express multiple aggregation semantics • unordered • sequential or priority order • alternative

18. RDF Containers • Bag • unordered grouping • Sequence • ordered grouping • Alternatives • alternate values • need to choose • at least one value • first value is default or preferred value

19. RDF - Bag • Unordered group • “Carl Lagoze and Stuart Weibel are co-authors” <BIB:Author> <Bag> <li> Carl Lagoze </li> <li> Stuart Weibel </li> </Bag> </BIB:Author>

20. RDF - Sequence • Ordered or priority group • “Carl Lagoze is primary author and Stuart Weibel is second author” <BIB:Author> <Seq> <li> Carl Lagoze </li> <li> Stuart Weibel </li> </Seq> </BIB:Author>

21. RDF - Alt • Client chooses one of several values • First value is default • “The distance is 15 kilometers or 9.3 miles” <DC:Coverage> <Alt> <li> 15KM </li> <li> 9.3M </li> </Alt> </DC:Coverage>

22. Formalizing the RDF model – Thinking in triples • RDF basic types • rdf:Resource – everything that can be identified (with a URI) • rdf:Property – specialization of a resource expressing a binary relation between two resources • rdf:statement – a triple with properties rdf:subject, rdf:predicate, rdf:object • An RDF statement is a triple consisting of a resource (subject), a property and a second resource (object) • (:s :p :o) • Expressible also as binary relations • P(S,O) – e.g., Title(R, “War & Peace”)

23. RDF triple model

24. RDF statements and basic types rdf:statement rdf:object rdf:subject rdf:predicate WYA DigitalLibraries creator rdf:property

25. Reification – Statements about statements CL rdf:statement assertedBy rdf:object rdf:subject rdf:predicate WYA DigitalLibraries creator rdf:property “CL says ‘WYA wrote Digital Libraries’”

26. From Graphs to Triples doris betty eve alice charles

27. Expressing Collection Primitives in Binary Relations

28. RDF Schemas • Declaration of vocabularies • properties defined by a particular community • characteristics of properties and/or constraints on corresponding values • Provides substructure for inferences based on existing triples • Schema language is an expression of basic RDF model • Schema Type System - Basic Types • Property, Class, SubClassOf, Domain, Range • Minimal (but extensible) at this time • Expressible in the RDF model and syntax

29. rdfs:label rdfs:label “Nom” “Author” rdfs:label “$100 $a” Schema Vocabularies • Enables communities to share machine readable tokens and locally define human readable labels. dc:Creator

30. Relationships among vocabularies dc:Creator marc:100 ms:director bib:Author

31. rdfs: subPropertyOf ms:director dc:Creator rdfs:label “Director” dc:Creator Relationships among vocabulary elements URI:R ms:director “John Smith”

32. RDF Schema: Specializing Properties • rdfs:subPropertyOf – allows specialization of relations • E.g., the property “father” is a subPropertyOf the property parent • subProperty semantics

33. Sub-Property Semantics

34. Constraints on Properties • Force objects to be of a certain type • rdfs:domain • Restricts the type of resources that may have a specific property • rdfs:range • Restricts the type of resources that may be the value of a specific property range

35. Inferences from Constraints doris betty eve alice charles

36. Inferences from Constraints

37. Class Hierarchy • rdfs:Class • Resources denoting a set of resources; range of rdf:type • rdfs:subClassOf • Create class hierarchy rdf:type rdf:type rdfs:class rdfs:subClassOf rdf:type rdf:type rdf:class rdf:class

38. Sub-Class Inferencing

39. Sub-class Inferencing Example

40. Storing and querying RDF models – Relational DB • Issues • Scalability: potentially huge # of triples • Tables: number, sparseness, joins • Queries: how and how expensive • Reification?

41. Storing and querying RDF models – SQUISH SELECT ?sal, ?t, ?x FROM http://ilrt.org/discovery/2000/11/rss-query/jobs-rss.rdf, http://ilrt.org/discovery/2000/11/rss-query/jobs.rss WHERE (job::advertises ?x ?y) (job::salary ?y ?sal) (job::title ?y ?t) AND ?sal > 55000 USING job for http://ilrt.org/discovery/2000/11/rss-query/jobvocab.rdf# http://swordfish.rdfweb.org:8085/rdfquery/index.html

42. Where do you stop? • Model provides enabling technology • Degree of metadata simplicity/complexity is a matter of: • Resource description communities needs, best-practice and experience • Organization/Institution’s Policy • Economics • Goals and requirements of implementation