Semantic Web introduction

Introduction

Semantic Web
&
Linked Data

Resource Description Framework
● W3C standard since 1999
● Graph data model
● Triples (graph elements)
● Subject: resource URI
● Property: resource URI
● Object: resource URI or literal value
● Multiple syntaxes
● Stored in triplestores
● SPARQL query language

Triples/Quads
Graph Subject Property Object
http://www.w3.org/ http://www.w3.org/ http://www.w3.org/
People/EM/contact# 1999/02/22-rdf- 2000/10/swap/pim/c
me syntax-ns#type ontact#Person
http://www.w3.org/ http://www.w3.org/ "Eric Miller"
People/EM/contact# 2000/10/swap/pim/c
me ontact#fullName
http://www.w3.org/ http://www.w3.org/ mailto:em@w3.org
me ontact#mailbox
http://www.w3.org/ http://www.w3.org/ "Dr."
me ontact#personalTit
le

Example from RDF Primer

Multiple syntaxes
● RDF/XML (the only W3C standard so far)
● Plain text
● Turtle (soon W3C standard)
● N-Triples
● Notation3
● Namespaces is a shorthand mechanism
● foo: http://example.org/somewhere/
● ex: http://example.org/somewhere/
● foo:bar = http://example.org/somewhere/bar
● foo:bar == ex:bar

RDF/XML syntax
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:contact="http://www.w3.org/2000/10/swap/pim/contact#">
<contact:Person rdf:about="
http://www.w3.org/People/EM/contact#me">
<contact:fullName>Eric Miller</contact:fullName>
<contact:mailbox rdf:resource="mailto:em@w3.org"/>
<contact:personalTitle>Dr.</contact:personalTitle>
</contact:Person>
</rdf:RDF>

Turtle syntax
@prefix contact: <http://www.w3.org/2000/10/swap/pim/contact#> .

<http://www.w3.org/People/EM/contact#me> a contact:Person ;
contact:fullName "Eric Miller" ;
contact:mailbox <mailto:em@w3.org> ;
contact:personalTitle "Dr." .

OWL (Web Ontology Language)
● Based on formal semantics
● Enables inference (reasoning)
● Open world assumption
● Unknown is not false but undefined
● Builds on RDF Schema
● Class (set of individuals)
● Property
– Datatype
– Object
● Instance (individual)

Ontologies
● Established, reusable vocabularies/schemas
● DublinCore: basic metadata
● FOAF: person and contact information
● SIOC: social media descriptions
● GoodRelations: e-commerce

SPARQL: RDF query language
● RDF graph pattern matching
● The only standard NoSQL query language
● SPARQL forms ● SPARQL Update forms
● SELECT ● INSERT DATA
● ASK ● DELETE DATA
● DESCRIBE ● INSERT/DELETE
● CONSTRUCT ● LOAD
● CLEAR

SPARQL example
PREFIX contact: <http://www.w3.org/2000/10/swap/pim/contact#>
SELECT *
{ ?person contact:mailbox ?mbox }

?person ?mbox
http://www.w3.org/People/EM/contact#me mailto:em@w3.org

RDF & SPARQL tools
● Frameworks
● Apache Jena
● Sesame
● Triplestores
● Dydra (cloud)
● Stardog
● Virtuoso
● BigData

Linked Data
● Linked Data = RDF + REST
● Linked Data platform (soon W3C standard)
● Item resources and container resources
● Implement HTTP methods
● Accept and return RDF descriptions
● Uniform generic web API
● The only global data integration approach

Linked Data usage
● Open datasources
● DBPedia
● Linked Life Data
● UK Open Data
● In companies
● BBC: Semantic Publishing
● IBM: Linked Data Basic Profile 1.0

Further reading
● RDF Primer
● OWL 2 Web Ontology Language Primer
● SPARQL by Example
● Learning SPARQL
● Linked Data: Evolving the Web into a Global Data S

Graphity
● Generic open-source Linked Data platform
● Independent from domain models and datasources
● Architecture
● Model: pure RDF, no object model (above RDF API)
– Generated SPARQL queries load RDF from triplestore
● View
– XSLT transforms RDF/XML to XHTML
● Controller
– JAX-RS web application matches requests, queries &
transforms

Thanks. Questions?
● Martynas Jusevičius
● Vilnius/Copenhagen
● martynas@graphity.org
● @pumba_lt

Semantic Web introduction

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