This document discusses linked data and its applications in the Web of Data. It describes the four principles of linked data: (1) using URIs to identify things, (2) using HTTP URIs so that these things can be looked up, (3) returning useful RDF information about each URI, and (4) including links to other URIs. Following these principles leads to interlinking data across the web and creating a Web of Data. The document outlines the increasing growth of the Web of Data since its inception in 2007.

1. Semantic Web
Technologies
Lecture 6: Applications in the Web of Data
04: Linked Data Engineering
Dr. Harald Sack
Hasso Plattner Institute for IT Systems Engineering
University of Potsdam
Spring 2013
This file is licensed under the Creative Commons Attribution-NonCommercial 3.0 (CC BY-NC 3.0)

2. 2
Lecture 6: Applications in the Web of Data
Open HPI - Course: Semantic Web Technologies
Semantic Web Technologies , Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

3. 3
04 - Linked Data Engineering
Open HPI - Course: Semantic Web Technologies - Lecture 6: Applications in the Web of Data
Semantic Web Technologies , Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

4. How to Get Data From the Web?
•Data can only be found on the Web,
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if it is available at some website
HTTP
HTML
JDBC
Browser
Web-Server
Database
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

5. How to Get Data From the Web?
•There is a number of different (proprietary) Web APIs, data
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exchange formats, and Mashups on top of that
Mashup
Web Web Web Web
API 1 API 2 API 3 API 4
Database 1 Database 2 Database 3 Database 4
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

6. In the Web today...
6 • Data is locked up in small data islands
• Other applications usually cannot access this data...
Database
Database
Database
Database
Database
Database
Database
Database
Database
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

7. How to Get Rid of Closed Data Islands on the Web?
•Apply semantic technologies:
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•to publish structured data on the web
•to draw connections from one data source to data from
other data sources
RDF Data RDF Data RDF Data RDF Data
RDF Links
RDF Links
RDF Links
Database 1 Database 2 Database 3 Database 4
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

8. Linked Data Principles
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(1) Use URIs as names for things.
(2) Use HTTP URIs, so that people can look up those
names.
(3) When someone looks up a URI, provide useful
information, using the standards (RDF, SPARQL)
(4) Include links to other URIs, so that they can
discover more things.
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

9. Linked Data Principles
(1) Use URIs as names for things.
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• URIs do not only identify documents but also arbitrary
objects of the real world as well as abstract concepts
http://yovisto.blogspot.com/
http://dbpedia.org/resource/Albert_Einstein
http://musicbrainz.org/artist/b10bbbfc-cf9e-42e0-be17-e2c3e1d2600d
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

10. Linked Data Principles
10 (2) Use HTTP URIs, so that people can look up those
names.
• HTTP URIs (URLs) as globally unique names enable
dereferencing of assiciated information in the Web
• via http Content Negotiation
• 303 URIs
http Response Code 303 ,See Other‘ (redirect)
• Hash URIs
http://example.com/Harald#me
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

11. Linked Data for Humans and Computers
■ URI should deliver information as well as for humans as for
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computers, i.e.
(Thing)
URI
Accept:
Accept: text/html
application/rdf+xml
(RDF data) (HTML page)
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

12. Linked Data for Humans and Computers
■ Server delivers different HTTP responses dependent of
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HTTP-Accept-Header (Content Negotiation)
http://www4.wiwiss.fu-berlin.de/bizer/pub/LinkedDataTutorial/
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

13. Linked Data for Humans and Computers
■ URI should deliver information as well as for humans as for
13
computers, i.e.
(Thing)
http://dbpedia.org/resource/Ernest_Hemingway
Accept:
Accept: text/html
application/rdf+xml
http://dbpedia.org/data/ http://dbpedia.org/page/
Ernest_Hemingway.rdf Ernest_Hemingway
(RDF data) (HTML page)
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

14. Linked Data Principles
(3) When someone looks up a URI, provide useful
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information, using the standards (RDF, SPARQL)
• RDF as universal data model for publishing structured
data on the Web
• Make all URIs in the RDF graph dereferencable
• Avoid RDF constructs that cause problems in Linked
Data context
• RDF Reification
• RDF Collections und Containers
• unnamed Blank Nodes
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

15. Linked Data Principles
(4) Include links to other URIs, so that they can
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discover more things.
• Link RDF references among data between different data
sources, to find information related by content
• Relationship Links
Links to external LOD Entitites related with the original
entity
• Identity Links
Links to external LOD Entities referring to the same
object or concept
• Vocabulary Links
Links to definitions of the original entity
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

16. The application of the Linked Data Principles
leads to a ,Web of Data‘
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Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

17. Development of the ,Web of Data‘
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May 2007
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

18. Development of the ,Web of Data‘
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Nov 2007
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

19. Development of the ,Web of Data‘
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Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

20. Development of the ,Web of Data‘
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July 2009
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

21. Development of the ,Web of Data‘
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September 2010
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

22. Development of the ,Web of Data‘ 300 Datasets
31B RDF Triples
504M Links
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September 2011
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

23. Linked Open Data
■ Public Linked Data resources in the Web, licensed as
23 „Creative Common CC-BY“
■ Tim Berners-Lee‘s 5-Star Criteria for Linked Open Data
★ Available on the web (whatever format) but with an open
licence, to be Open Data
★ ★ Available as machine-readable structured data
(e.g. excel instead of image scan of a table)
★ ★ ★ as (2) plus non-proprietary format (e.g. CSV instead of excel)
★ ★ ★ ★ All the above plus: use open standards from W3C
(RDF and SPARQL) to identify things, so that people can point at
your stuff
★ ★ ★ ★ ★ All the above, plus: link your data to other people’s data to
provide context
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

24. Linked Open Data
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Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

25. Semantic Mashups
□ Semantic Mashups are applications that use linked RDF
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data from various data sources.
□ in difference to interfaces and exchange formats or ordinary
Web APIs, Linked Data offers the following benefits:
□ a flexible and standardized data format (RDF)
□ standardized access mechanism (http)
□ possibility to put links (RDF-Links) among different data
sources
» enables navigation
» is supported by search engines (crawler)
» enables expressive search facilities over the crawled
data and beyond
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

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05 - Linked Data Engineering (Part 2)
Open HPI - Course: Semantic Web Technologies - Lecture 6: Applications in the Web of Data
Semantic Web Technologies , Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam