RESOURCES DESCRIPTION FRAMEWORK (RDF)

Hala Skaf-Molli, Prof

Responsable ALMA

Hala.Skaf@univ-nantes.fr

http://pagesperso.ls2n.fr/~skaf-h

Responsable GDD

Gestion de données distribuées

LS2N, Bât 34, Bureau 403

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Open Knowledge Graphs

and Semantic Web

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Knowledge representation model

Semantic Web Stack

Query language to retrieve information from KGs.

Uniform Resource Identifier (URI)

• Entities uniquely identified, worldwide
• The same entity can have multiple identifiers, but the same identifier shall always mean the same entity

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Nantes

Nantes

Nantes City

• A Uniform Resource Identifier (URI) is a string of characters (ASCII) used to identify a resource on the Internet
• A URI can take the form of a URL

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http://imitators.org/Elephant/L3

http://dbpedia/resource/Nantes

http://insee.org/Nantes

URI Standard

• An Internationalized Resource Identifier is a generalization of a URI that allows a much wider range of characters Unicode (including accents, non-Latin alphabets, etc.)

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IRI Standard

• World Wide Web Consortium (W3C) Recommendation since 1998
• RDF is a data model
• Originally used for metadata for web resources, then generalized
• Basic unit is triple.

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Resource Description Framework

for Knowledge Representation

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Resource Description Framework

for Knowledge Representation

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Facts are stored in triple format (subject predicate object).

Semantic Web Stack

An RDF Triple has a subject, a predicate and an object.

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Nantes

identifies

identifies

the relationship between two resources

identifies

Pays de la Loire

What is an RDF triple ?

• Subject : URI or blank node (unnamed individual)
• Predicate (property, relationship): URI
• “locatedIn”, “birthPlace”, “written by”, “age”, “title”, etc.
• Object : URI, blank node or Literals

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Nantes

identifies

identifies

locatedIn

“Pays de la Loire”

What is an RDF triple?

• An RDF triple asserts a property of a resource
• In English: Nantes is located in Pays de la Loire
• In Logic: locatedIn(Nantes,Pays de la Loire)

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identifies

identifies

identifies

locatedIn

Pays de la Loire

Nantes

What is an RDF triple ?

• An RDF graph is a set of RDF triples
• RDF Graph is labeled directed graph:
• Subject and object of a triple correspond to nodes
• Predicate corresponds to directed edge from subject to object with a label given by the predicate.

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What is an RDF graph ?

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Nantes

Pays de La Loire

locatedIn

Example of an RDF Graph

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RDF Data set

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Owl:sameAS

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Linked Open Data knowledge Graph

https://lod-cloud.net/

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These principles have been coined by Tim Berners-Lee in the design issue note Linked Data. The principles are:

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• Use URIs as names for things
• Use HTTP URIs so that people can look up those names.
• When someone looks up a URI, provide useful information.
• Include links to other URIs. so that they can discover more things.

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Source: https://www.w3.org/wiki/LinkedData

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Linked Data Principles

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http://blog.sindice.com/2009/07/22/sigma-live-views-on-the-web-of-data/

• Turtle
• RDF/XML
• N-Quads
• N-Triples
• JSON-LD
• RDFa (RDF in HTML)

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RDF can be serialized in different ways

• A namespace prefix is an abbreviation for the prefix of a URI.

@prefix city : http://dbpedia.org/resource/

@prefix location: http://lodpaddle.org/

@prefix region: http://region.org/

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city:Nantes location:locatedIn region:Paysdelaloire

Namespace Prefixes

• The default namespace prefix is just a colon.

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@prefix :< http://dbpedia.org/resource/>.

@prefix location: <http://lodpaddle.org/rdf/pred#>.

@prefix region: <http://region.org/>.

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:Nantes location:locatedIn region:Paysdelaloire

Default Prefix

RDF Turtle:

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@prefix : <http://lodpaddle.org/> .

@prefix admin: <http://admin.org/>.

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:Nantes :population “283025” .

:Nantes admin:hasMoyer :JohannaRolland.

:Nantes :locatedIn <http://region.org/PaysdeLaLoire> .

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RDF Turtle

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Turtle

@prefix foaf: <http://xmlns.com/foaf/0.1/> .

@prefix ex: <http://example.org/> .

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ex:Alice a foaf:Person ;

foaf:name "Alice" ;

foaf:knows ex:Bob .

ex:Bob a foaf:Person ;

foaf:name "Bob" .

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JSON-LD

JSON-LD : JavaScript Object Notation for Linked Data (compact)

{

"@context": {

"foaf": "http://xmlns.com/foaf/0.1/",

"name": "foaf:name",

"knows": "foaf:knows",

"type": "@type"

},

"@id": "http://example.org/Alice",

"type": "foaf:Person",

"name": "Alice",

"knows": {

"@id": "http://example.org/Bob",

"type": "foaf:Person",

"name": "Bob"

}

}

• RDF can also be stored in XML format

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<?xml version="1.0"?>

<rdf:RDF

xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"

xmlns:prop=“http://lodpaddle.org/” >

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<rdf:Description rdf:about=“http://lodpadlle.org/Nantes”>

<prop:location rdf:resource=“http://region.org/paysdelaloire” />

</rdf:Description>

</rdf:RDF>

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Properties of X are listed inside an rdf:Description about=X

Namespaces become XML namespaces

RDF/XML Syntax

List of triples, easy to download and to parse.

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<http://lodpaddle.org/Nantes> <http://admin.org/population> “283025” .

<http://lodpaddle.org/Nantes> <http://admin.org/hasMoyer> <http://admin.org/JohannaRolland .

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RDF N-Triples

https://www.w3.org/TR/n-triples/

A triple <s,p,o> is interpreted as a First Order Logic fact p(s,o).

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locatedIn(Nantes,Pays de la Loire)

hasMayor(Nantes, Johanna Rolland)

population(Nantes,”283025”)

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RDF Semantics

• First order logic(FOL): A triple <s p o> without blank node is interpreted as P(s,o) : grounded atomic formula
• Blank nodes in subject or object are interpreted as existential variables
• Example:
• @prefix foaf :<http://xmlns.com/foaf/0.1/> .
• @prefix dc: <http://purl.org/dc/elements/1.1/> .

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• :Pierre foaf:knows _:p .
• _:p foaf:name “John Smith” .
• _:p dc:wrote _:b .
• _:b dc:title “Introduction to Java” .

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RDF Semantics

@prefix p: <http://lodpaddle.or/> .

@prefix rdf: <http://w3c.org/1999/02/22-rdf-syntax-ns#>.

@prefix xsd: <http://www.w3c.org/2001/XMLSchema# >.

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p:Nantes p:poplulation “283025”^^xsd:integer ;

p:hasMoyer p:JohannaRolland ;

rdf:type p:City .

P:Rennes p:population “208022”^^xsd:integer;

p:hasMayor p:NatalieAppéré .

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Use XML types

The predicate rdf:type relates resources to their classes

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@prefix p: <http://lodpaddle.or/> .

@prefix rdf: <http://w3c.org/1999/02/22-rdf-syntax-ns#>.

@prefix xsd: <http://www.w3c.org/2001/XMLSchema# >.

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p:Nantes p:poplulation “283025”^^xsd:integer ;

p:hasMoyer p:JohannaRolland ;

rdf:type p:City .

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Type of a resource

@prefix book: <http://example.org/>

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book:42 book:title    ’’Life Questions@en’’ .

book:42 book:title   ’’Questions sur la vie@fr’’ .

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Identifier the language of a value

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Source: http://www.w3.org/TR/turtle/#BNodes

Identifier the language of a value

�

• A named Graph gives a context for a set of triples
• Identifier a set of triples by an URI
• Two formats : TriG and N-Quads

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Named Graph

�

TriG: extension of Turtle

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@prefix foaf : <http://xmlns.com/foaf/0.1/> .

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GRAPH <http://example.org/bob>

{

_:b foaf:name ‘’Bob’’ .

}

GRAPH <http://example.org/alice>

{

_:a foaf:name ‘’Alice’’ .

}

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Named Graph in TriG

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N-quads statements are a sequence of RDF terms representing the subject, predicate, object and graph label of an RDF Triple

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@prefix foaf : <http://xmlns.com/foaf/0.1/> .

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_:b foaf:name ‘’Bob’’ <http://example.org/bob >.

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_:a foaf:name ‘’Alice’’ <http://example.org/alice> .

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Named Graph in N-Quads

RDF is flexible, schema-free to represent knowledge as triples (subject predicate object)

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dbr:Jules_Verne rdf:type schema:Person;

dbo:birthPlace dbr:Nantes;

dbo:birthDate "1828-02-08";

dbo:author dbr:Around_the_World_in_Eighty_Days,

dbr:From_the_Earth_to_the_Moon;

dbp:nationality "French";

owl:sameAs wikidata:Jules_Verne.

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@prefix dbr:<http://dbpedia.org/resource/> .

@prefix rdf:<http://www.w3.org/1999/02/22-rdf-syntax-ns#> .

@prefix schema: <http://www.schema.org/>.

@prefix dbo:<http://dbpedia.org/ontology/>.

@prefix owl: <http://www.w3.org/2002/07/owl#> .

URI: <http://dbpedia.org/resource/Jules_Verne>

• RDF is domain-independent
• RDF is bottom-up
• RDF has a graph-based data model
• RDF has a decentralized philosophy and allows incremental building of knowledge, and its sharing and reuse
• Linked data is a giant, global data graph defined in RDF

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RDF Advantages

• TD RDF (OLD)
• Sujet Projet Dana
• SPARQL

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TD/Project and Next lecture