openhpi 6.4 - linked data engineering

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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


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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?


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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


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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


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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?


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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.


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(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/




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(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


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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)

http://dbpedia.org/resource/Ernest_Hemingway









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■Server delivers different HTTP responses dependent ofHTTP-Accept-Header (Content Negotiation)

http://www4.wiwiss.fu-berlin.de/bizer/pub/LinkedDataTutorial/





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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/data/Ernest_Hemingway.rdf

http://dbpedia.org/page/Ernest_Hemingway



















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(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


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(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


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The application of the Linked Data Principles leads to a ,Web of Data‘


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Development of the ,Web of Data‘

May 2007


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Nov 2007



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July 2009



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September 2010



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September 2011

300 Datasets 31B RDF Triples504M Links



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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

★

★ ★

★ ★ ★★ ★ ★ ★

★ ★ ★ ★ ★


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Linked Open Data


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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


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05 - Linked Data Engineering (Part 2)Open HPI - Course: Semantic Web Technologies - Lecture 6: Applications in the Web of Data

openhpi 6.4 - linked data engineering

Documents

structured data

e2c3e1d2600dvo semantic

mevorlesung semantic

web of data17may

linked data principlesleads

linked data principles8

linked data principles10

linked data principles4