This document provides an introduction to linked data and RDF. It discusses: 1. The principles of linked data, which involve using URIs to identify things and including links to other related resources. 2. The goals of linked data, which are to transfer information between machines without loss of meaning by identifying data on the web using shared vocabularies and RDF. 3. An overview of RDF, which structures data as subject-predicate-object triples and can be serialized in formats like RDF/XML and Turtle to represent typed links between resources.

1. Linked Data and RDF
Semantic Engineering Seminar WS 2013/14
Daniel Nüst
daniel.nuest@wwu.de

2. Linked Data
WWW > Web of Documents
CSV, XML, HTML tables >>> Web of Data
Typed Links, to & from >>> global data graph
LOD

3. Principles
1. Use URIs to denote things.
2. Use HTTP URIs [#, /] so that these things can be
referred to and looked up ("dereferenced") by
people and user agents.
3. Provide useful information [metadata (aliases,
DC terms, technical: means of access, formats)]
about the thing when its URI is dereferenced,
leveraging standards such as RDF, SPARQL.
4. Include links to other [!] related things (using
their URIs) when publishing data on the Web
[reusing vocabularies].
http://en.wikipedia.org/wiki/Linked_data

4. 2.46 billion pieces of information (RDF triples)
http://lod-cloud.net/ http://dbpedia.org/

5. http://lov.okfn.org/dataset/lov/index.html

6. http://lov.okfn.org/dataset/lov/details/vocabulary_geo.html

7. RDF (.rdf)
“HTML for data”
the thing
the value
the property
Goals/Applications
transfer information between machines (not people) without loss of meaning,
“identified on the web”
Vocabularies (terms) for statements
Serializations
http://www.w3.org/TR/rdf-primer/
<Subject> <Predicate> <Object>

8. http://www.w3.org/TR/rdf-primer/
http://www.example.org/index.html has a creator whose value is John Smith

9. http://www.example.org/index.html has a creator whose value is John Smith
http://www.w3.org/TR/rdf-primer/
http://www.example.org/index.html has a creation-date whose value is August 16, 1999
http://www.example.org/index.html has a language whose value is English

10. <http://www.example.org/index.html> <http://purl.org/dc/elements/1.1/creator> <http://www.example.org/staffid/8574
<http://www.example.org/index.html> <http://www.example.org/terms/creation-date> "August 16, 1999" .
<http://www.example.org/index.html> <http://purl.org/dc/elements/1.1/language> "en" .
(shared) Vocabularies
namespace URI: http://www.example.org/
convention
ex:index.html dc:creator exstaff:85740 .
ex:index.html exterms:creation-date "August 16, 1999" .
ex:index.html dc:language "en" .
fy:joefy.iunm ed:dsfbups fytubgg:85740 .
http://www.w3.org/TR/rdf-primer/
prefix ex:
prefix dc:
namespace URI: http://purl.org/dc/elements/1.1/
prefix exterms: namespace URI: http://www.example.org/terms/
prefix exstaff: namespace URI: http://www.example.org/staffid/

11. John Smith has a an age whose value is 27
<http://www.example.org/staffid/85740> <http://www.example.org/terms/age>
"27"^^<http://www.w3.org/2001/XMLSchema#integer> .
ex:index.html exterms:creation-date "1999-08-16"^^xsd:date .
http://www.w3.org/TR/rdf-primer/
exstaff:85740 exterms:age "27"^^xsd:integer .

12. Concepts Things you should have heard about …
Data types
Expression of simple facts
Entailment
[Literals, URIrefs, RDF/XML, graphs]
http://www.w3.org/TR/rdf-concepts
Blank nodes

13. http://www.w3.org/TR/rdf-primer/

14. http://www.w3.org/TR/rdf-primer/
RDF/XML

15. Turtle (.ttl)
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>.
@prefix contact: <http://www.w3.org/2000/10/swap/pim/contact#>.
<http://www.w3.org/People/EM/contact#me>
rdf:type contact:Person;
contact:fullName "Eric Miller";
contact:mailbox <mailto:em@w3.org>;
contact:personalTitle "Dr.".
http://www.w3.org/2007/02/turtle/primer/

16. <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdfsyntax-ns#"
xmlns:geo="http://www.w3.org/2003/01/geo/wgs84_pos#">
<geo:Point>
<geo:lat>55.701</geo:lat>
<geo:long>12.552</geo:long>
</geo:Point>
</rdf:RDF>
http://www.w3.org/2003/01/geo/#example
Geo and RDF

17. <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
xmlns:geo="http://www.w3.org/2003/01/geo/wgs84_pos#"
xmlns:dc="http://purl.org/dc/elements/1.1/"
xmlns="http://xmlns.com/foaf/0.1/">
<Person>
<name>Dan Brickley</name>
<homepage dc:title="Dan's home page"
rdf:resource="http://danbri.org/"/>
<based_near geo:lat="51.47026" geo:long="2.59466"/>
<rdfs:seeAlso rdf:resource="http:/danbri.org/foaf.rdf"/>
<!-- more RDF here, using any RDF vocabularies -->
</Person>
</rdf:RDF>
http://www.w3.org/2003/01/geo/#example
Geo, FOAF & DC

18. Resources and references > see handout!
THANKS!

20. Linked data applications
browsers – navigate/traverse data sources using
links/RDF triples (connecting web of {documents, data})
search engines – start of the navigation
human-oriented (like Google…)
application-oriented (reuse indexing for different apps)
domain applications
Dbpedia Mobile, Revyu, DERI pipes, …

21. RDFa 1.0 Example
http://en.wikipedia.org/wiki/RDFa

22. RDFs and OWL
RDF Schema > http://en.wikipedia.org/wiki/RDF_Schema
Web Ontology Language > http://en.wikipedia.org/wiki/Web_Ontology_Language
more expressive
See also https://www.cambridgesemantics.com/de/semantic-university/rdfs-vs.-owl