Linked Data Tutorial

Faculty of Mathematics and PhysicsCharles University in Prague

Linked Data Tutorial*Tomáš Knap, Jindřich Mynarz, Martin Nečaský, Jakub Stárka

February 16, 2012

(*Partially based on slides of Chris Bizer [8])

16th February 2012 | Linked Data Tutorial 2

Motivation


Motivational ScenarioBasic data Employees Departments Public

contracts Budget Expenses

WWW page of the institution

Business Register ÚFIS Buyer‘s

Profile ISVZUS gov.cz

Data Consumer: Show me suppliers of the public contracts for the Ministry of Finance (MF) in the region Liberec. Show me the data on the Google maps in iPhone. For every public contract, I am also looking for the aggregation of all the payments made by MF, link to their budget and responsible person.

• Where can I get the data about public contracts, responsible persons, expenses, and budget of MF?

• How should I aggregate and link the data? • How can I observe the data on the map?


Current Common Practise

1 – MF public contracts

2 – MF public contracts + employees

3 - Expenses

Consumer did not discovered

?

?

?

Information Integration very time consuming, boring, and ineffective!

Basic data Employees Departments Public






Linked Data - Basics


Linked Data

• Set of best practices for publishing structured data on the Web in accordance with the general architecture of the Web using Semantic Web technologies and standards Semantic Web is the goal, Linked Data provides

the means to reach the goal


Linked Data Principles

1. Use URIs as names for things2. Use HTTP URIs so that people can look up those

names.3. When someone looks up a URI, provide useful RDF

information4. Include RDF statements that link to other URIs so

that they can discover related things.

[Tim Berners-Lee, http://www.w3.org/DesignIssues/LinkedData.html, 2006]


Architecture of the Classic Web Single global information space Small set of simple standards:

‒ HTTP URI • globally unique ID • retrieval mechanism

‒ HTML as document format‒ Hyperlinks to connect everything

Applications work on top of the complete information space


Web 2.0 APIs and Mashups No single global dataspace Shortcomings:

‒ API have proprietary interfaces‒ No hyperlinks between data items

within different APIs‒ Mashups are based on a fixed set

of data sources

Web APIs slice the Web into Walled Gardens!


Linked Data

• Extend the Web with a single global dataspace By using RDF to publish structured data on the Web By setting links between data items within different data

sources. Physically distributed, behaves like single dataspace


RDF Data Model

• Flexible graph-based data model [2]

• HTTP URIs take the role of global primary keys.

pd:cygri = http://richard.cyganiak.de/foaf.rdf#cygri dbpedia:Berlin = http://dbpedia.org/resource/Berlin


Resolving URIs over the Web

• The HTTP protocol brings together identification and retrieval


Following Links deeper into the Web


Pubby – Linked Data Browser

http://dbpedia.org/page/Český_Krumlov


Properties of the Web of Linked Data

• Global, distributed data space build on a simple set of standards RDF, URIs, HTTP

• Entities are connected by links creating a global data graph that spans data sources enables the discovery of new data sources

• Data-coexistence Everyone can publish data to the Web of Linked Data Everyone can express their personal view on things


Linked Data Deployment on the Web..

Is it real?


W3C Linking Open Data Project

• Grassroots community effort to Publish existing open license datasets as Linked

Data on the Web Interlink things between different data sources


Linked Data Cloud 2007



http://richard.cyganiak.de/2007/10/lod/lod-datasets_2011-09-19_colored.pdfhttp://thedatahub.org/


More Statistics

http://stats.lod2.eu/stats


Uptake in Governmental Domain

• The EU is publishing LinkedData EuroStat

‒ http://estatwrap.ontologycentral.com/

• National efforts The Government is releasing public data

‒ http://data.gov.uk/‒ Lots of initiatives in Great Britain

Budget in Germany‒ http://bund.offenerhaushalt.de/

Open Data in Catalonia‒ http://opendata.gencat.cat/en/dades-obertes.html

http://estatwrap.ontologycentral.com/

http://estatwrap.ontologycentral.com/

http://data.gov.uk/

http://bund.offenerhaushalt.de/

http://opendata.gencat.cat/en/dades-obertes.html


Data.gov.uk

http://data.gov.uk/organogram/cabinet-office


Linked Data Applications

? ? ??Linked Data Browsers


Search Engines - Sig.ma

http://sig.ma


Mashups – Public Contracts On the Map

http://gd.projekty.ms.mff.cuni.cz:2021/new/map.html


Mashups – Crime, Transport, Education

http://apps.seme4.com/see-uk/


Other Applications

• Browsers: Disco Hyperdata Browser

‒ http://www4.wiwiss.fu-berlin.de/rdf_browser/ OpenLink RDF Browser

‒ http://ode.openlinksw.com/

• Search Engines Falcons

‒ http://ws.nju.edu.cn/falcons/ Watson

‒ http://watson.kmi.open.ac.uk/WatsonWUI/

• Mashups

http://www4.wiwiss.fu-berlin.de/rdf_browser/



http://ode.openlinksw.com/

http://ode.openlinksw.com/

http://ws.nju.edu.cn/falcons/




Linked Data Applications - SummaryLinked Data Browsers Search Engines Linked Data Mashups


Publishing Linked Data


Publishing Tasks – Bizer 38

• 1. Make data available as RDF via HTTP Requires ways to serialize RDF data model

• 2. Set RDF links pointing at other data sources• 3. Make your data self-descriptive


RDF/XML

• W3C Recommendation, 2004 [2]


Turtle Syntax

@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .@prefix dataModel: <http://www.w3.org/2000/10/swap/pim/contact#> .@prefix myContact: <http://www.w3.org/People/EM/contact#> .

myContact:me rdf:type dataModel:Person ;dataModel:fullName "Eric Miller".dataModel:mailbox <mailto:[email protected]>.dataModel:personalTitle "Dr.".

• W3C Team Submission, 2011, [4]


RDFa

• A way to directly add RDF to XHTML pages Provides new attributes to handle additional

markup• W3C Recommendation, 2008 [5]• HTML is not extendable

• most RDFa parsers will recognize RDFa attributes in any version of HTML


RDFa

• Provides new attributes to handle additional markup, reuses existing About, resource, … Href, src, …

• Used with any supported element, prefered: Span, div (in the body) a (linking element) Meta, link (in the header)


RDFa Example

• XHTML page http://example.com/alice/posts/42

• Original XHTML codeAll content on this site is licensed under <a href="http://cc.org/licenses/by/3.0/"> a Creative Commons License </a>.

• XHTML + RDFaAll content on this site is licensed under <a rel=“cc:license" href="http://cc.org/licenses/by/3.0/"> a Creative Commons License </a>.

• RDF triples destilled from XHTML+RDFa<http://example.com/alice/posts/42> cc:license <http://cc.org/licenses/by/3.0/>.


RDF store + Linked Data Interface

• Virtuoso + pubby


D2R server

• A way how to publish data in relational databases as Linked Data

• Requests from the Web are rewritten into SQL queries via the mapping. on-the-fly translation eliminates the need for replicating the data into a dedicated RDF

triple store.


Publishing Tasks

1. Make data available as RDF via HTTP2. Set RDF links pointing at other data sources3. Make your data self-descriptive


2. Set RDF links

<http://dbpedia.org/resource/Berlin> owl:sameAs <http://sws.geonames.org/2950159> .

• There are tools to help you generate links Silk [6]


Publishing Tasks

1. Make data available as RDF via HTTP2. Set RDF links pointing at other data sources3. Make your data self-descriptive


3. Make your data self-descriptive

• Increase the usefulness of your data and ease data integration

• Aspects of self-descriptiveness 1. Reuse terms from common vocabularies 2. Enable clients to retrieve the schema 3. Publish schema mappings for proprietary terms 4. Metadata

‒ Provide provenance metadata‒ Provide licensing metadata‒ Provide data-set-level metadata using voiD


About Vocabularies

• We have to be able to define the meaning of the subject, properties Vocabularies, e.g. Public contracts ontology


Public Contracts Ontology

http://purl.org/procurement/public-contracts#


RDFS

• RDFS = RDF Schema W3C recommendation

‒ http://www.w3.org/TR/rdf-schema/ Vocabulary for RDF

‒ Definition of classes• is:Student rdf:type rdfs:Class

‒ Definition of properties• is:name rdf:type rdfs:Property

‒ Domains and ranges of properties• is:name rdfs:domain is:Student• is:name rdfs:range xsd:string


OWL

• OWL = Web Ontology Language W3C recommendation

‒ http://www.w3.org/TR/owl2-overview/ Ontologies

‒ More complex constructs• Class or property equivalences• Cardinality restrictions• …


3. Make your data self-descriptive

• Increase the usefulness of your data and ease data integration

• Aspects of self-descriptiveness 1. Reuse terms from common vocabularies 2. Enable clients to retrieve the schema 3. Publish schema mappings for proprietary terms 4. Metadata

‒ Provide provenance metadata‒ Provide licensing metadata‒ Provide data-set-level metadata using voiD


3.1 Reuse Terms from Common vocabularies• Common Vocabularies

Friend-of-a-Friend for describing people and their social network SIOC for describing forums and blogs SKOS for representing topic taxonomies Organization Ontology for describing the structure of organizations GoodRelations provides terms for describing products and business

entities Music Ontology for describing artists, albums, and performances Review Vocabulary provides terms for representing reviews

• Common sources of identifiers (URIs) for real world objects LinkedGeoData and Geonames locations GeneID and UniProt life science identifiers DBpedia wide range of things


3.2 Enable Clients to retrieve the Schema

• Clients can resolve the URIs that identify vocabulary terms in order to get their RDFS or OWL definitions.

• If we discover in data URI:<http://opendata.cz/data/p6/contract/ocz_art_5161> http://purl.org/procurement/public-contracts#awardDate "2011-11-11"^^<http://www.w3.org/2001/XMLSchema#date> ;

• We resolve the URI and get the definition:

RDFS or OWL definition


3.3 Publish Schema Mappings

pc:Tender a owl:Class ;rdfs:subClassOf gr:Offering .

pc:AwardCriterion a owl:Class ; owl:equivalentClass loted:AwardCriteria.

• Simple Mappings: rdfs:subClassOf, rdfs:subPropertyOf owl:equivalentClass, owl:equivalentProperty

• Complex mappings – R2R [7]


3.4 Metadata

• Licenses • Data Provenance• Dataset description


Consuming Linked Data


Overview

• URI -> Description Pubby

• Keyword -> Description Sig.ma

• SPARQL query language [8] SQL for RDF databases


SPARQL Example

• Contracts of the given supplier


SPARQL Example - Result


Issues of the Simple Consuming Scenarios

• How to aggregate the data if the links are missing, the data models (ontologies) differs?

• How to deal with data quality? Everybody can say whatever he wants!

• Solution: We are developing an infrastructure for cleaning, linking, and aggregating Linked Data Reusing existing technologies, such as Silk


ODCleanStore

• Cleaning the data Custom cleaners

• Linking the data Silk

• Graphical user interface

• Smart data consuming Data aggregation (due to

links, ontology mappings)

Conflict resolution Data provenance


Motivational Scenario - RecallBasic data Employees Departments Public





Data Consumer: Show me suppliers of the public contracts for the Ministry of Finance (MF) in the region Liberec. Show the data on the Google maps in iPhone. For every public contract, I am looking for the aggregation of all the payments made by MF, link to their budget and responsible person. • Where can I get the data about public

contracts, responsible persons, expenses, and budget of MF?

• How should I aggregate and link the data? • How can I observer the data on the map?


Goal

ODCleanStore

Basic data Employees Departments Public






Conclusions


Linked Data vs. Open Data

• Open data – 3 stars! 4th star: Single and flexible model (RDF) is missing 5th star: Links

Open data are raw data, which are freely available on the Web to:• Everyone• Anytime• For whatever purpose


Conclusions and Take Away MessageThe Power Of Linked Data (5 star data)

• Web-scale data publishing with web-based discovery mechanisms

• Distributed annotation – make comments about observations, data series, points on the map

• Easy to reuse Huge potential when connecting to the cloud, linking the data,

the benefits are growing as the amount of data published as Linked Data is increasing

• Integration on data level• Easy to extend (new data properties as required, no need

to be planned up-front)• Easy to merge – no name clashes!


Future Steps

• If you managed to get interesting data, try to publish them as Linked Data! We can help you with the whole lifecycle – creating, publishing,

maintenance of the data Just create RDF data, we will publish it for you Just let us know (send us the data), we can publish it Publish data in the same way, but use global identifiers

according to LD principles• When the infrastructure (ODCleanStore) is ready, you can

just send us the RDF data using web service and we will do all the other stuffs – clean, link, and provide aggregated views.


Thank You!


References

• Textbook: Tom Heath, Christian Bizer: Linked Data: Evolving the Web into a Global Data Space. http://linkeddatabook.com/

• [2] http://www.w3.org/TR/rdf-primer/• [3] http://www.w3.org/TR/REC-rdf-syntax/• [4] http://www.w3.org/TeamSubmission/turtle/• [5] http://www.w3.org/TR/rdfa-syntax/• [6] http://www4.wiwiss.fu-berlin.de/bizer/silk/• [7] http://www.w3.org/TR/rdf-sparql-query/• [8] http://

static.lod2.eu/isslod/Bizer-LOD2-IndianSummerSchool.pdf

http://linkeddatabook.com/

http://linkeddatabook.com/

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



http://www.w3.org/TR/REC-rdf-syntax/

http://www.w3.org/TR/REC-rdf-syntax/

http://www.w3.org/TeamSubmission/turtle/



http://www.w3.org/TR/rdfa-syntax/

http://www.w3.org/TR/rdfa-syntax/

http://www4.wiwiss.fu-berlin.de/bizer/silk/

http://www4.wiwiss.fu-berlin.de/bizer/silk/

http://www.w3.org/TR/rdf-sparql-query/

http://www.w3.org/TR/rdf-sparql-query/

http://static.lod2.eu/isslod/Bizer-LOD2-IndianSummerSchool.pdf

http://static.lod2.eu/isslod/Bizer-LOD2-IndianSummerSchool.pdf

Linked Data Tutorial

Education

Transcript of Linked Data Tutorial