resource description framework building the semantic web
DESCRIPTION
Resource Description Framework Building the Semantic Web. CS 502 – 20020226 Carl Lagoze – Cornell University. Acknowledgements: Eric Miller Dieter Fensel. Illustration is a type of contribution. M. Doe illustrated the book “Best Stories”. - PowerPoint PPT PresentationTRANSCRIPT
Cornell CS 502
Resource Description FrameworkBuilding the Semantic Web
CS 502 – 20020226Carl Lagoze – Cornell University
Acknowledgements:Eric MillerDieter Fensel
Cornell CS 502
Motivating the “Semantic Web”
M. Doe illustrated the book “Best
Stories”Mary Doe
animated the cartoon “Best Stories – the
movie”
Illustration is a type of
contribution
animation is a type of
contribution
M. Doe and Mary Doe are
pseudonyms forSusan Mann
Show me the works to which Susan
Mann contributed?
Cartoons and Books are types
of Works
Cornell CS 502
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
• Primitives permit semantic inferencing • Expressible in machine readable manner (e.g.,
XML)
Cornell CS 502
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
RDF Data Model
• Imposes structural constraints on the expression of application data models– for consistent encoding, exchange and processing of
metadata– Provides for structural interoperability
• Enables resource description communities to define their own semantics
Cornell CS 502
RDF Data Model
• Directed labeled graphs• Model elements
– Resource– Property– Value– Statement– Containers
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RDF Model Primitives
ResourceProperty
ValueResource
Statement
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Simple Example
ResourceAuthor
“Eric”
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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
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RDF Model Example #1
URI:R“CIMI Presentation”
Title
Creatordc:
dc:
“Eric Miller”
Cornell CS 502
RDF Syntax Example #1
URI:R“CIMI Presentation”
Title
Creatordc:
dc:
“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>
Cornell CS 502
“Eric Miller”
RDF Model Example #2
URI:R
URI:ERIC
“[email protected]”“Eric Miller”
“OCLC”
bib:Emailbib:Affbib:Name
URI:OCLC
“CIMI Presentation”Title
Creatoroa:
dc:
Cornell CS 502
<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#”> <Description about = “URI:R”> <dc:Title> CIMI Presentation </dc:Title> <oa:Creator> <Description> <bib:Name> Eric Miller </bib:Name> <bib:Email> [email protected] </bib:Email> <bib:Aff resource = “http://www.oclc.org” /> </Description> </oa:Creator> </Description></RDF>
RDF Syntax Example #2
Cornell CS 502
“Eric Miller”
RDF Model Example #3
URI:R
URI:ERIC
“[email protected]”“Eric Miller”
“OCLC”
bib:Emailbib:Affbib:Name
URI:OCLC
“CIMI Presentation”Title
Creator admin:By
admin:On
“LOC”
“03-09-99”
admin:For“...”
dc:
dc:
Cornell CS 502
RDF Containers
• Permit the aggregation of several values for a property
• Express multiple aggregation semantics– unordered– sequential or priority order– alternative
Cornell CS 502
RDF Containers
• Permit the aggregation of several values for a property
• Express multiple aggregation semantics– unordered– sequential or priority order– alternative
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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
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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>
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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>
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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>
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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”)
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RDF triple model
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RDF statements and basic types
WYA
creator
DigitalLibraries
rdf:s
ubje
ct
rdf:p
red
icate
rdf:object
rdf:statement
rdf:property
“CL says ‘WYA wrote Digital Libraries’”
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Reification – Statements about statements
“CL says ‘WYA wrote Digital Libraries’”
WYA
creator
DigitalLibraries
rdf:s
ubje
ct
rdf:p
red
icate
rdf:object
rdf:statement
rdf:property
CLassertedBy
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From Graphs to Triples
alice
betty
charles
doris
eve
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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
• 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
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
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Relationships among vocabularies
dc:Creator
ms:director
marc:100
bib:Author
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Relationships among vocabulary elements
URI:R “John Smith”ms:director
dc:Creatorms:director
rdfs:subPropertyOf
rdfs:label“Director”
dc:Creator
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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
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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
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Inferences from Constraints
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Class Hierarchy
• rdfs:Class– Resources denoting a set of resources; range of
rdf:type
• rdfs:subClassOf– Create class hierarchy
rdf:type rdf:typerdfs:class
rdfs:subClassOf
rdf:type
rdf:class
rdf:type
rdf:class
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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?
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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
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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