1. Resource Description Framework Building the Semantic Web
CS 502 –
Carl Lagoze – Cornell University
Acknowledgements: Eric Miller Dieter Fensel
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2. 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?
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3. Components of the Semantic Web
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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)
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5. 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
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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)
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7. Directed labeled graphs Model elements
RDF Data Model
Directed labeled graphs
Model elements
Resource
Property
Value
Statement
Containers
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8. Resource Resource Value Statement RDF Model Primitives Property
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9. Simple Example
Resource
Author
“Eric”
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10. 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
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11. RDF Model Example #1 URI:R dc: Title “CIMI Presentation” Creator
“Eric Miller”
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12. 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>
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13. 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
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14. <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>
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15. 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
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16. 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
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17. 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
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18. RDF Containers Bag Sequence Alternatives unordered grouping
alternate values
need to choose
at least one value
first value is default or preferred value
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19. “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>
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20. 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>
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21. 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>
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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”)
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23. RDF triple model
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24. RDF statements and basic types
rdf:object
rdf:subject
rdf:predicate
WYA
Digital Libraries
creator
rdf:property
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25. Reification – Statements about statementsCL
rdf:statement
assertedBy
rdf:object
rdf:subject
rdf:predicate
WYA
Digital Libraries
creator
rdf:property
“CL says ‘WYA wrote Digital Libraries’”
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26. From Graphs to Triples
doris
betty
eve
alice
charles
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27. Expressing Collection Primitives in Binary Relations
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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
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29. 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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30. Relationships among vocabularies
dc:Creator
marc:100
ms:director
bib:Author
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31. Relationships among vocabulary elements
dc:Creator
ms:director
rdfs:
subPropertyOf
rdfs:label
“Director”
dc:Creator
URI:R
ms:director
“John Smith”
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32. 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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33. Sub-Property Semantics
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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
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35. Inferences from Constraints
doris
betty
eve
alice
charles
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36. Inferences from Constraints
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37. 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
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38. Sub-Class Inferencing
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39. Sub-class Inferencing Example
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40. 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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41. 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
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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
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