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Resource Description Framework Building the Semantic Web
CS 502 – Carl Lagoze – Cornell University Acknowledgements: Eric Miller Dieter Fensel Cornell CS 502
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Motivating the “Semantic Web”
Illustration is a type of contribution M. Doe illustrated the book “Best Stories” Mary Doe animated 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? Cornell CS 502
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Components of the Semantic Web
Cornell CS 502
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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) Cornell CS 502
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Syntax for interchange of data Schema Type system (schema model)
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 Cornell CS 502
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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) Cornell CS 502
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Directed labeled graphs Model elements
RDF Data Model Directed labeled graphs Model elements Resource Property Value Statement Containers Cornell CS 502
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Resource Resource Value Statement RDF Model Primitives Property
Cornell CS 502
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Simple Example Resource Author “Eric” Cornell CS 502
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XML is one well-supported syntax There are syntax alternatives
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 Cornell CS 502
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RDF Model Example #1 URI:R dc: Title “CIMI Presentation” Creator
“Eric Miller” Cornell CS 502
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URI:R RDF Syntax Example #1 dc: Title “CIMI Presentation” Creator
“Eric Miller” <RDF xmlns = “ xmlns:dc = “ <Description about = “URI:R”> <dc:Title> CIMI Presentation </dc:Title> <dc:Creator> Eric Miller </dc:Creator> </Description> </RDF> Cornell CS 502
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URI:R URI:ERIC URI:OCLC
RDF Model Example #2 URI:R oa: dc: Title “CIMI Presentation” Creator URI:ERIC oclc.org” “Eric Miller” “OCLC” bib: bib:Aff bib:Name “Eric Miller” URI:OCLC Cornell CS 502
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<RDF xmlns = “http://www.w3.org/TR/WD-rdf-syntax#”
RDF Syntax Example #2 <RDF xmlns = “ xmlns:dc = “ xmlns:bib = “ xmlns:oa = “ <Description about = “URI:R”> <dc:Title> CIMI Presentation </dc:Title> <oa:Creator> <Description> <bib:Name> Eric Miller </bib:Name> <bib: > </bib: > <bib:Aff resource = “ /> </Description> </oa:Creator> </RDF> Cornell CS 502
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RDF Model Example #3 Reification
admin:By admin:On “LOC” “ ” admin:For “...” URI:R dc: Title “CIMI Presentation” Creator URI:ERIC oclc.org” “Eric Miller” “OCLC” bib: bib:Aff bib:Name “Eric Miller” URI:OCLC Cornell CS 502
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Permit the aggregation of several values for a property
RDF Containers Permit the aggregation of several values for a property Express multiple aggregation semantics unordered sequential or priority order alternative Cornell CS 502
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Permit the aggregation of several values for a property
RDF Containers Permit the aggregation of several values for a property Express multiple aggregation semantics unordered sequential or priority order alternative Cornell CS 502
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RDF Containers Bag Sequence Alternatives unordered grouping
alternate values need to choose at least one value first value is default or preferred value Cornell CS 502
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“Carl Lagoze and Stuart Weibel are co-authors”
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> Cornell CS 502
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Ordered or priority group
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> Cornell CS 502
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Client chooses one of several values First value is default
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> Cornell CS 502
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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”) Cornell CS 502
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RDF triple model Cornell CS 502
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RDF statements and basic types
rdf:object rdf:subject rdf:predicate WYA Digital Libraries creator rdf:property Cornell CS 502
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Reification – Statements about statements
CL rdf:statement assertedBy rdf:object rdf:subject rdf:predicate WYA Digital Libraries creator rdf:property “CL says ‘WYA wrote Digital Libraries’” Cornell CS 502
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From Graphs to Triples doris betty eve alice charles Cornell CS 502
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Expressing Collection Primitives in Binary Relations
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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 Cornell CS 502
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Schema Vocabularies Enables communities to share machine readable tokens and locally define human readable labels. dc:Creator “Nom” rdfs:label “Author” rdfs:label “$100 $a” rdfs:label Cornell CS 502
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Relationships among vocabularies
dc:Creator marc:100 ms:director bib:Author Cornell CS 502
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Relationships among vocabulary elements
dc:Creator ms:director rdfs: subPropertyOf rdfs:label “Director” dc:Creator URI:R ms:director “John Smith” Cornell CS 502
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RDF Schema: Specializing Properties
rdfs:subPropertyOf – allows specialization of relations E.g., the property “father” is a subPropertyOf the property parent subProperty semantics Cornell CS 502
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Sub-Property Semantics
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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 Cornell CS 502
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Inferences from Constraints
doris betty eve alice charles Cornell CS 502
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Inferences from Constraints
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Class Hierarchy rdfs:Class rdfs:subClassOf
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 Cornell CS 502
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Sub-Class Inferencing
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Sub-class Inferencing Example
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Storing and querying RDF models – Relational DB
Issues Scalability: potentially huge # of triples Tables: number, sparseness, joins Queries: how and how expensive Reification? Cornell CS 502
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Storing and querying RDF models – SQUISH
SELECT ?sal, ?t, ?x FROM WHERE (job::advertises ?x ?y) (job::salary ?y ?sal) (job::title ?y ?t) AND ?sal > 55000 USING job for Cornell CS 502
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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 Cornell CS 502
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