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Dr. Harald Sack
Hasso Plattner Institute for IT Systems Engineering
University of Potsdam
Spring 2013
Semantic Web Technologies
Lecture 6: Applications in the Web of Data04: Linked Data Engineering
Semantic Web Technologies , Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
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Lecture 6: Applications in the Web of DataOpen HPI - Course: Semantic Web Technologies
Semantic Web Technologies , Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
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04 - Linked Data EngineeringOpen HPI - Course: Semantic Web Technologies - Lecture 6: Applications in the Web of Data
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
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•Data can only be found on the Web, if it is available at some website
Database
Web-Server
JDBC
HTTPHTML
Browser
How to Get Data From the Web?
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
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How to Get Data From the Web?
•There is a number of different (proprietary) Web APIs, data exchange formats, and Mashups on top of that
Database 1
WebAPI 1
WebAPI 2
WebAPI 3
WebAPI 4
Database 2 Database 3 Database 4
Mashup
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
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In the Web today...
•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
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•Apply semantic technologies:
•to publish structured data on the web
•to draw connections from one data source to data from other data sources
Database 1 Database 2 Database 3 Database 4
RDF Data RDF Data RDF Data RDF Data
RDF Links
RDF Links
RDF Links
How to Get Rid of Closed Data Islands on the Web?
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
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Linked Data Principles
(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
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Linked Data Principles
(1) Use URIs as names for things.
•URIs do not only identify documents but also arbitrary objects of the real world as well as abstract concepts
http://dbpedia.org/resource/Albert_Einstein
http://musicbrainz.org/artist/b10bbbfc-cf9e-42e0-be17-e2c3e1d2600d
http://yovisto.blogspot.com/
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
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Linked Data Principles
(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 URIshttp Response Code 303 ,See Other‘ (redirect)
•Hash URIshttp://example.com/Harald#me
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
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Linked Data for Humans and Computers
■URI should deliver information as well as for humans as for computers, i.e.
URI
Accept: application/rdf+xml Accept: text/html
(Thing)
(RDF data) (HTML page)
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
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■Server delivers different HTTP responses dependent ofHTTP-Accept-Header (Content Negotiation)
http://www4.wiwiss.fu-berlin.de/bizer/pub/LinkedDataTutorial/
Linked Data for Humans and Computers
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
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■URI should deliver information as well as for humans as for computers, i.e.
Accept: application/rdf+xml Accept: text/html
(Thing)
(RDF data) (HTML page)
http://dbpedia.org/resource/Ernest_Hemingway
http://dbpedia.org/data/Ernest_Hemingway.rdf
http://dbpedia.org/page/Ernest_Hemingway
Linked Data for Humans and Computers
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
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Linked Data Principles
(3) When someone looks up a URI, provide useful 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
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Linked Data Principles
(4) Include links to other URIs, so that they can discover more things.
•Link RDF references among data between different data sources, to find information related by content
•Relationship LinksLinks to external LOD Entitites related with the original entity
• Identity LinksLinks to external LOD Entities referring to the same object or concept
•Vocabulary LinksLinks to definitions of the original entity
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
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The application of the Linked Data Principles leads to a ,Web of Data‘
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
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Development of the ,Web of Data‘
May 2007
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
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Nov 2007
Development of the ,Web of Data‘
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
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Development of the ,Web of Data‘
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
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July 2009
Development of the ,Web of Data‘
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
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September 2010
Development of the ,Web of Data‘
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
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September 2011
300 Datasets 31B RDF Triples504M Links
Development of the ,Web of Data‘
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
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Linked Open Data
■Public Linked Data resources in the Web, licensed as„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
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Linked Open Data
Vorlesung Semantic Web, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam
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□Semantic Mashups are applications that use linked RDF 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
Semantic Mashups
Semantic Web Technologies , 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