Linked Data

Linking Open Data
Danny Ayers
SemAst2009

Obligatory Children Slide

Credits:
Many slides derived from those of
Tom Heath, Michael Hausenblas, Chris Bizer, Richard Cyganiak, Olaf Hartig

Quote
Linked Data is the Semantic Web done right, and the Web done right.”
- Tim Berners-Lee

Introduce the concept of Linked Data
Highlight why you would want to publish Linked Data on the Web
Introduce the principles and best practices of publishing Linked Data on the Web
Demonstrate the creation and consumption of Linked Data
Answer your burning Linked Data publishing questions
Objectives

Overview
From a Web of Documents to a Web of Data
Web APIs, Microformats, and Linked Data
Linked Data Deployment on the Web
What data is out there?
Applications
What is being done with the data?

Classic Data : in silos Image: Bob Jagensdorf, http://flickr.com/photos/darwinbell/, CC-BY

The Classic Web
Single global information space
URLs as
globally unique IDs
retrieval mechanism
HTML as shared content format
Hyperlinks
Shortcomings
Content is not well structured
You can not ask expressive queries
You can not process content within applications
B C HTML HTML HTML Web Browsers Search Engines hyperlinks A

What do we actually want? Use the Web like a single global database.

Solution
Web APIs
Microformats
Linked Data
Publish structured data directly on the Web Different Approaches

Web APIs

Mashups
Positive
APIs expose structured data
APIs enable new applications
Negative
Usually proprietary interfaces
Mashups are based only on fixed set of sources
You can't usually set hyperlinks between data objects
Mashup Up Web API A Web API B Web API C Web API D

Web APIs slice the Web into separate data silos Image: Bob Jagensdorf, http://flickr.com/photos/darwinbell/, CC-BY

What do we want? Use the Web as a single global database using what we know works on the Web

Connecting Worlds One Web! Data Documents

What works on the Web?
Uniform Identifiers (URIs)
Common Interface Protocol (HTTP)
Standard Representation Formats (HTML, Atom/RSS etc)

What works on the Web?
The Hyperlink

Evolving the Link
<a href=” http://example.org/home.html “>
Home Page
</a>
page.html home.html

Evolving the Link
<a href=”http://example.org/home.html”
rel=”home”>
Home Page
</a>
page.html home.html home

Microformats
Embed structured data into HTML pages.
hCard, hCalender, hReview, XFN, …
Compatible with the idea of the Web as single information space.
Shortcomings
Only a fixed set of microformats exist
No direct way to connect data items
<div class="vevent"> <span class="summary">bdigital</span> <abbr class="dtstart" title="2008-05-20">May 20</abbr> - <abbr class="dtend" title="2007-05-22">22</abbr> </div>

Evolving the Link
<rdf:Description
rdf:about=” http://example.org/page ”>
<x:home
rdf:resource=” http://example.org/home ” />
</rdf:Description>
page home x:home

Linked Data B C Thing typed links A D E typed links typed links typed links Thing Thing Thing Thing Thing Thing Thing Thing Thing
Use Semantic Web technologies to
publish structured data on the Web,
set links between data from one data source to data within other data sources .

RDF Relations
<rdf:Description
rdf:about=” http://example.org/page ”>
<x:home
rdf:resource=” http://example.org/home ” />
</rdf:Description>
x:home subject object http://example.org /page ... http://example.org /home ...

Identifiers
Identification by Description
Non-HTTP URIs
HTTP URIs

Linked Data Principles
Use URIs as names for things
Use HTTP URIs so that people can look up those names.
When someone looks up a URI, provide useful information.
Include links to other URIs. so that they can discover more things.
Tim Berners-Lee 2007
http://www.w3.org/DesignIssues/LinkedData.html

The RDF Data Model Richard Cyganiak dbpedia:Berlin foaf:name foaf:based_near foaf:Person rdf:type pd:cygri

Data objects are identified with HTTP URIs pd:cygri Richard Cyganiak dbpedia:Berlin foaf:name foaf:based_near foaf:Person rdf:type pd:cygri = http://richard.cyganiak.de/foaf.rdf#cygri dbpedia:Berlin = http://dbpedia.org/resource/Berlin

Follow Your Nose... Richard Cyganiak dbpedia:Berlin foaf:name foaf:based_near foaf:Person rdf:type pd:cygri dp:Cities_in_Germany 3.405.259 dp:population skos:subject

Dereferencing URIs over the Web Richard Cyganiak dbpedia:Berlin foaf:name foaf:based_near foaf:Person rdf:type dbpedia:Hamburg dbpedia:Muenchen skos:subject skos:subject pd:cygri dp:Cities_in_Germany 3.405.259 dp:population skos:subject

Universal Connector <resourceB> rdfs:seeAlso <resourceA>

Universal Connector <resourceB> rdfs:seeAlso <resourceA> foaf:Person rdf:type

Take Care! <resourceB> owl:sameAs <resourceA>

The Disco – Hyperdata Browser

Semantic Web Specifications
HTTP + URIs
RDF + RDFs
OWL
SKOS
SPARQL
RDFa
GRDDL
Turtle/N3
Coming soon: POWDER, OWL2, RIF

What of Web Services? “ Web APIs Are Just Web Sites” - Paul Downey Linked Data is exposed as (very simple) RESTful services

What of RDF Stores? A triplestore is just a cache of a chunk of the Semantic Web Convenient for data merging, querying (SPARQL) and inference See also: Semantic Web Client Library

What of the Real World? source: http://danbri.org/words/2008/04/15/300 based on timbl 1994

W3C Linking Open Data Project
Community effort to
publish existing open license datasets as Linked Data on the Web
interlink things between different data sources

LOD Datasets on the Web: May 2007

LOD Datasets on the Web: August 2007

LOD Datasets on the Web: February 2008

LOD Datasets on the Web: September 2008

LOD Datasets on the Web: March 2009

Spotlight: Geonames
over 8 million geographical locations
feature hierarchy

Spotlight: DBpedia
extracts structured data from Wikipedia.
covers over 2.2 million concepts from various domains.

Example RDF Links
RDF links from DBpedia to other data sources
RDF link from a FOAF profile to DBpedia
<http://dbpedia.org/resource/Berlin> owl:sameAs <http://sws.geonames.org/2950159> . <http://richard.cyganiak.de/foaf.rdf#cygri> foaf:topic_interest <http://dbpedia.org/resource/Semantic_Web> . <http://dbpedia.org/resource/Tim_Berners-Lee> owl:sameAs <http://www4.wiwiss.fu-berlin.de/dblp/resource/person/100007> .

Universities and Research Institutes
Massachusetts Institute of Technology (USA)
University of Southampton (UK)
Freie Universität Berlin (DE)
DERI (IRE)
KMi, Open University (UK)
University of London (UK)
Universität Hannover (DE)
University of Pennsylvania (USA)
Universität Leipzig (DE)
Universität Karlsruhe (DE)
Joanneum (AT)
University of Toronto (CA)
Organizations publishing Linked Data
Companies
BBC (UK)
OpenLink (UK)
Zitgist (USA)
Talis (UK)
Garlik (UK)
Mondeca (FR)
Cyc Foundation (USA)

Applications B C Thing typed links A D E typed links typed links typed links Thing Thing Thing Thing Thing Thing Thing Thing Thing Search Engines Linked Data Mashups Linked Data Browsers
What can I do with this?

Linked Data Browsers
Tabulator Browser (MIT, USA)
Marbles (FU Berlin, DE)
OpenLink RDF Browser (OpenLink, UK)
Zitgist RDF Browser (Zitgist, USA)
Disco Hyperdata Browser (FU Berlin, DE)
Fenfire (DERI, Irland)

Tabulator

Linked Data Mashups
Domain-specific applications
- using Linked Data from the Web

DBpedia Mobile
Geospatial entry point into the Web of Data
Starts with DBpedia, Revyu and Flickr data

Web of Data Search Engines
Falcons (IWS, China)
Sindice (DERI, Ireland)
MicroSearch (Yahoo, Spain)
Watson (Open University, UK)
SWSE (DERI, Ireland)
Swoogle (UMBC, USA)

Falcons

Why publish Linked Data on the Web?
Your data becomes part of a single global data space (the Web of Data = Semantic Web)
People can use various data browsers to explore your data
Your data is crawled by Semantic Web search engines and can be used by independent applications
People start setting links to your data, which allows more people to find and use your data

Why publish Linked Data on the Web?
Linked Data builds on the classic architecture of the Web
Linked Data is more generic then Web APIs or Microformats
Builds on standards in contrast to proprietary Web APIs
Enables applications that work against an unbound set of data sources and incorporate new data sources as they become available on the Web

Linked Data Principles
Tim Berners-Lee 2007
http://www.w3.org/DesignIssues/LinkedData.html

Example : Source Data

Example : First Pass @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> . @prefix owl: <http://www.w3.org/2002/07/owl#> . @prefix x: <http://purl.org/stuff/astro#> . x:Megrez rdf:type x:A3_dwarf ; x:magnitude "3.1" ; x:partOf [ rdf:type x:Constellation ; x:hasName "Ursa Major" ] . (RDF Turtle/N3 Syntax)

Example : Vocabulary @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> . @prefix x: <http://purl.org/stuff/astro#> . x:Star rdf:type rdfs:Class . x:Constellation rdf:type rdfs:Class . x:A3_Dwarf rdfs:subClassOf x:Star . x:magnitude rdf:type rdf:Property . x:partOf rdf:type rdf:Property . x:hasName rdf:type rdf:Property .

But...
Existing vocabularies and resource URIs are likely to be well-linked already – reuse is good!

Example : Better Linkage @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> . @prefix x: <http://purl.org/stuff/astro#> . @prefix astro: <http://archive.astro.umd.edu/ont/astronomy.owl#> . @prefix foaf: <http://xmlns.com/foaf/0.1/> . @prefix dolce: <http://www.loa-cnr.it/ontologies/DOLCE-Lite.owl#> . @prefix dbpedia: <http://dbpedia.org/resource/> . dbpedia:Delta_Ursae_Majoris rdf:type x:A3_Dwarf ; foaf:name "Megrez"; x:magnitude "3.1" ; dolce:part-of dbpedia:Ursa_Major ; rdfs:seeAlso <http://www.dcs.gla.ac.uk/workshops/semast09> . dbpedia:Ursa_Major rdf:type astro:Constellation .

Mass-Publication Techniques
Generally either:
bulk conversion
live mapping from existing databases

New Vocabularies : Scovo Statistical Core Vocabulary

"It is important to look as it as an interconnection bus, and it hasn't started working in earnest until one person's data is being used by some other unplanned use. This unexpected reuse is the measure." - Tim Berners-Lee, re. State of the Semantic Web Finishing Quotes

"Engineer for serendipity." - Roy T. Fielding, re. REST Finishing Quotes

http://hyperdata.org/astronomy/ Related Links etc.

Linked Data

by Danny Ayers on Mar 02, 2009

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