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Web of Data, Linked Data, Semantic Web

Knowledge Representation in Practice

*A HTML5 presentation by Antoine Zimmermann

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Web de données, Données Liées, Web Sémantique

La représentation de connaissances en pratique

*Une présentation HTML5 par Antoine Zimmermann

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From a Web of Documents to a Web of Data

Switch to Firefox

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Can we query the Web?

Who are the widows of murdered American presidents? 

SELECT ?widow
FROM WorldWideWeb
WHERE
  (?widow marriedTo ?person) AND
  (?person isPresidentOf UnitedStates) AND
  (?person killedBy ?someKiller)

What were the most popular songs when Obama was elected? 

SELECT ?song, COUNT(?vote)
FROM WorldWideWeb
WHERE
  (?vote inFavourOf ?song) AND
  (?vote madeAt ?date) AND
  (Obama electedAt ?date)
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Resource Description Framework

Simple data model: everything is triples

subject predicate object .

Examples:

emse:az foaf:knows ujm:gravier .
ujm:gravier foaf:based_near _:location1 .
_:location1 geo:latitude "40.442673" .
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Where can I find data?

Switch to Firefox

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SPARQL Query Language

Who are the widows of assassinated US presidents?

PREFIX db: <http://dbpedia.org/property/>
PREFIX yago: <http://dbpedia.org/class/yago/>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
SELECT ?widow
FROM http://dbpedia.org/
FROM http://data.gov.us/
WHERE {
  ?widow db:spouse ?person .
  ?person rdf:type yago:AssassinatedUnitedStatesPresidents .
}
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Schemas and Ontologies: RDFS and OWL

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RDF Schema

Define a vocabulary (a set of specific URIs) which has a fixed meaning

  • Typed instances: 
    emse:az rdf:type foaf:Person .
  • Class hierarchy: 
    foaf:Person rdfs:subClassOf foaf:Agent .
  • Property hierarchy: 
    skos:prefLabel rdfs:subPropertyOf rdfs:label .
  • Property domain and range: 
    mo:conductor rdfs:domain mo:Performance .
    mo:encodes rdfs:range mo:Signal .
  • + other terms with an informal specification
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RDF Schema

Reasoning with RDFS: Example

emse:az foaf:knows dblp:Christophe_Gravier .
foaf:Person rdfs:subClassOf foaf:Agent .
foaf:knows rdfs:range foaf:Person .
foaf:knows rdfs:domain foaf:Person .

Which entails:

emse:az rdf:type foaf:Person .
emse:az rdf:type foaf:Agent .
dblp:Christophe_Gravier rdf:type foaf:Person .
dblp:Christophe_Gravier rdf:type foaf:Agent .
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Web Ontology Language (OWL)

Define a much richer vocabulary with a specific meaning

  • All RDFS terms (rdfs:subClassOf, etc) can be used in OWL
  • Additional features on classes: disjointness, union, intersection, attribute restrictions, value restrictions, cardinality restriction, etc.
  • Additional features on properties: functional, inverse functional, inverse of, symmetric, assymmetric, etc.
  • Additional features on instances: equality, inequality

Reasoning with OWL

  • There can be contradictions in OWL: can be used to (somewhat) constrain the data
  • We can infer equality! 
    emse:~zimmmermann owl:sameAs dblp:Antoine_Zimmermann .
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How does the course work?

Hands-on sessions: learning by doing

Practical sessions to build a Semantic Web applications

Reverse course: labwork first, theory next

(if we have time) more on KR languages

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