An introduction to Linked (Open) Data

An Introduction to
Linked (Open) Data
Ali Khalili, PhD
Knowledge Representation & Reasoning Group
VU University Amsterdam

Why do we need the Data Web?
Linked Open Data 2Ali Khalili
Linked Open Data

Linked Open Data
Problem: Try to search for these things on the current Web:
• Apartments near Dutch-English bilingual childcare in Amsterdam

Linked Open Data
Web
Server
funda.nl kindergarden.nl
Has data about childcare
in Amsterdam.
Knows about real
estate offers in the
Netherlands.
DBDB
HTMLHTML
Web
Server

Linked Open Data
Web
Server
funda.nl kindergarden.nl
Has data about childcare
in Amsterdam.
Knows about real
estate offers in the
Netherlands.
DBDB
HTMLHTML
Web
Server
RDF

Why do we need the Data Web? (con.)
Linked Open Data
• Researchers working on Semantic Web topics in the Middle East.
• Side effects of some drugs with a speciﬁc chemical compound
prescribed for certain diseases.
• Who are mayors of central European towns elevated more than 1000m?
• Which movies are starring both Brad Pitt and Angelina Jolie?
• All soccer players, who played as goalkeeper for a club that has a
stadium with more than 40.000 seats and who are born in a country with
more than 10 million inhabitants
• …

Why do we need the Data Web? (con.)
Linked Open Data
• Researchers working on Semantic Web topics in the Middle East.
• Side effects of some drugs with a speciﬁc chemical compound
prescribed for certain diseases.
• Who are mayors of central European towns elevated more than 1000m?
• Which movies are starring both Brad Pitt and Angelina Jolie?
• All soccer players, who played as goalkeeper for a club that has a
stadium with more than 40.000 seats and who are born in a country with
more than 10 million inhabitants
• …
Information is available on the Web,
but opaque to current search.

Evolution of the Web
Linked Open Data
https://mcgratha.wordpress.com/

Linked Open Data
1998: Semantic Web Road map

Linked Open Data
1998: Semantic Web Road map
2006: emergence of Data Web

Linked Data
Linked Open Data
• A set of best practices for publishing data on the Web.

Linked Data
Linked Open Data
• A set of best practices for publishing data on the Web.
• Follows 4 simple principles:
1. Use URIs as names (identiﬁers) for conceptual things.
2. Use HTTP URIs so that users can look up (dereference) those
names.
3. When someone looks up a URI, provide useful information,
using the open standards such as RDF, SPARQL, etc.
4. Include links to other URIs, so that users can discover more
things.

Linked Data Principles
Linked Open Data
WWW World

5 Open Data
Linked Open Data
make your stuff available on the Web (whatever format)
under an open license
make it available as structured data
(e.g., Excel instead of image scan of a table)
make it available in a non-proprietary open format
(e.g., CSV as well as of Excel)
use Linked Data format
(URIs to identify things, RDF to represent data)
link your data to other people’s data to provide context
http://5stardata.info/

5 Open Data
Linked Open Data

Linked Open Data Cloud
Linked Open Data
http://lod-cloud.net/

Statistics
Linked Open Data
http://lodlaundromat.org/
http://stats.lod2.eu/
more than 3426 datasets

Linked Open Data
Hands-on

Linked Open Data
Ranking of universities Amount of funding acquired by universities?
Hands-on

Linked Open Data
Ranking of universities Amount of funding acquired by universities?
Hands-on
Make a sorted list of all universities in the Netherlands
displaying their recent rankings (e.g. CWTS Leiden Ranking or
Times World University Rankings) together with the amount of
EC contributions on H2020 projects?

Linked Open Data
Interlinking
Enrichment
Quality
Analysis
Evolution
Exploration
Extraction
Storage/
Querying
Authoring
Linked (Open) Data
Lifecycle
http://stack.linkeddata.org/

Linked Open Data Lifecycle
Exploration

• Search
• Browse
• Visualize
Exploration

Search for Linked Data
Linked Open Data Lifecycle Exploration

http://swoogle.umbc.edu/

Search in Linked Data
http://www.wolframalpha.com/
Question Answering Systems

http://lov.okfn.org/

http://lotus.lodlaundromat.org

http://demo.ld-r.org/lotus

Data hub http://datahub.io
search for data, register published datasets, create and manage groups of datasets…
Exploration

Search for/in Linked Data

https://www.google.com/cse/

http://schema.org/
http://bl.ocks.org/danbri/1c121ea8bd2189cf411c

Browsing Linked Data
Loupe http://loupe.linkeddata.es/
discovering the type of data contained in a dataset, its structure, and the vocabularies used…
Exploration

Linked Data Reactor http://ld-r.org
a component-based framework to view, browse and edit Linked Data
Exploration

Exhibit http://www.simile-widgets.org/exhibit/
Exploration

Visualizing Linked Data
Using existing visualisations for structured data
e.g. Sgvizler http://dev.data2000.no/sgvizler/

Using graph-based visualizations
e.g. RelFinder http://www.visualdataweb.org/relﬁnder/relﬁnder.php

Hands-on
1. List of all universities in the Netherlands
2. University Rankings (e.g. CWTS Leiden Ranking or Times
World University Rankings)
3. H2020 EU projects repository
Explore Web of Data for the following data sources:

Extraction

from Unstructured sources
Linked Open Data Lifecycle Extraction
…After leaving Apple, Jobs took a few of its members with him to
found NeXT, a computer platform development company based in
Redwood City, specializing in state-of-the-art computers for higher-
education and business markets. In addition, Jobs helped to initiate
the development of the visual effects industry when he funded the
spinout of the computer graphics division of George Lucas's
company Lucasfilm in 1986. The new company, Pixar, would
eventually produce the first fully computer-animated film, Toy Story…
NLP, Text mining, Annotation

Named Entity Recognition

foundedBy
Relation Extraction

http://spotlight.dbpedia.org
http://bioportal.bioontology.org/annotator

Contextual visualizations
e.g. Zemanta https://wordpress.org/plugins/zemanta

http://nlp2rdf.org
Interoperability between NLP tools, language
resources and annotations
NLP Interchange Format (NIF)
& Disambiguation (NERD)
http://nerd.eurecom.fr/

from Semi-structured sources

Resource Property Value

Multi-lingual
• 38.3m things in 125 languages
• 23.8m are localized descriptions of things in the English DBpedia
• English DBpedia describes 4.58m things (68,091,260 statements)
Multi-domain
1,445,000 persons, 735,000 places (including 478,000 populated places), 411,000 creative works
(including 123,000 music albums, 87,000 ﬁlms and 19,000 video games), 241,000 organizations
(including 58,000 companies and 49,000 educational institutions), 251,000 species and 6,000 diseases
Linked Open Data Lifecycle Extraction DBpedia

• Ad-hoc
• DBpedia extraction framework
• Generic
• OpenReﬁne

from Structured sources

Tripliﬁcation by Materialization

Tripliﬁcation by SPARQL-to-SQL-Rewriting

Tripliﬁcation
• Relational Database to RDF
R2RML: RDB to RDF Mapping Language
http://www.w3.org/TR/r2rml/
• D2R Server: Accessing databases with SPARQL &
as Linked Data
http://d2rq.org/
• Sparqlify
deﬁning RDF views on relational databases
http://sparqlify.org/

Hands-on
1. University Rankings (e.g. CWTS Leiden Ranking or Times
World University Rankings)
2. H2020 EU projects repository
Triplify the following data sources:

Storage & Querying

Relational Databases vs. Triple Stores
Linked Open Data Lifecycle Storage/Querying
• A relational databases’ (e.g. MySQL, PostgreSQL, Oracle)
natural representation is a collection interlinked tables.
• A triple stores’ (e.g. OpenSesame, AllegroGraph, Neo4j)
natural representation is a multi-relational network, or graph.

Relational Databases vs. Triple Stores
• Relational databases tend to not maintain public
access points (some might provide Web APIs).
• Triple stores maintain public access points called
SPARQL end-points.
• Relational database users tend to not publish their
schemas.
• Triple store users tend to reuse and extend public
schemas called ontologies.

Existing Triple Stores
• Native triple stores
4Store, AllegroGraph, BigData, Jena TDB, Sesame,
Stardog, OWLIM and uRiKa
• RDBMS-backed triple stores
Jena SDB, IBM DB2 and OpenLink Virtuoso
• NoSQL triplestores
CumulusRDF

SPARQL – SQL for the Linked Data
What can be done with SPARQL that can't be done with SQL?

What can be done with SPARQL that can't be done with SQL?
• SPARQL queries are considerably better aligned with users’ mental
models of a domain.

• SPARQL allows the conceptual data model to be fully explored
through queries.

• SPARQL allows the conceptual data model to be fully explored
through queries.
- example:workPhone rdfs:subPropertyOf example:phone

- example:cellPhone rdfs:subPropertyOf example:phone

- example:homePhone rdfs:subPropertyOf example:phone

• Queries that have to traverse a chain of connections are
particularly complex in SQL while very simple in SPARQL.

• In addition to SELECT, INSERT and DELETE, SPARQL supports
ASK queries.
• SPARQL includes syntax (i.e. SERVICE) to call two or more data
sources within a single query.
• …

SPARQL Query Interface
http://yasgui.org/

Hands-on
Write a SPARQL query to return a list of all
universities in the Netherlands sorted by name.
DBpedia Endpoints:
http://dbpedia.org/sparql
http://live.dbpedia.org/sparql
http://dbpedia-live.openlinksw.com/sparql
http://lod.openlinksw.com/sparql

Authoring

Semantic Wikis
Linked Open Data Lifecycle Authoring
• Semantic (Text) Wikis
Authoring of semantically annotated text
• Semantic Data Wikis
Direct authoring of structured information
(i.e. RDF, RDF-Schema, OWL)
http://semantic-mediawiki.org/
http://aksw.org/Projects/OntoWiki

OntoWiki use case: Catalogus Professorum
Linked Open Data Lifecycle Authoring Semantic Data Wiki
The Catalogus Professorum Lipsiensis – Semantics-based Collaboration and Exploration for Historians

Semantic Content Annotation
WYSIWY - What You See Is What You GetG

Semantic Content Annotation
WYSIWY - What You See Is What You Mean
http://rdface.aksw.org
M

LD-R Framework
http://ld-r.org

Interlinking

Interlinking
• The degree to which entities that represent the same
concepts are linked to each other.
• “Connecting things that are somehow related”
• Methods
• Automatic, Semi-automatic, Manual
• Universal, Domain-speciﬁc
<http://dbpedia.org/resource/VU_University_Amsterdam>
<https://www.wikidata.org/entity/Q1065414>
SameAs

Interlinking Methods
• Ontology Matching
• establish links between ontologies underlying two
data sources.
• Instance Matching (Link Discovery)
• discover links between instances contained in two
data sources.

SILK Framework
http://silk-framework.com/
Interlinking Semi-automatic

LIMES Framework
http://aksw.org/Projects/LIMES
Interlinking Semi-automatic

Hands-on
Linked Open Data Lifecycle Interlinking
1. Universities in CWTS Leiden Ranking or Times World
University Rankings
2. Universities in H2020 EU projects
Reconcile the following resources against DBpedia:

Enrichment

ORE (Ontology Repair and Enrichment)
Linked Open Data Lifecycle Enrichment
http://ore.aksw.org/

Quality Analysis

Linked Data Quality Dimensions
Quality Assessment for Linked Data: A Survey

Luzzu
http://eis.iai.uni-bonn.de/Projects/Luzzu
Quality Analysis Tools

RDFUnit
http://aksw.org/Projects/RDFUnit
Quality Analysis Tools

Evolution

EvoPat – Pattern based KB Evolution
Linked Open Data Lifecycle Evolution
• Inspired by Software Refactoring
• Agile Knowledge Engineering
• Basic & compound evolution patterns
http://link.springer.com/chapter/10.1007%2F978-3-642-17746-0_41

Linked Open Data
Interlinking
Enrichment
Quality
Analysis
Evolution
Exploration
Extraction
Storage/
Querying
Authoring
Linked (Open) Data
Lifecycle
http://stack.linkeddata.org/
Life Cycle

Hands-on Result
Linked Open Data

Linked Open Data

References
Linked Open Data
• http://slidewiki.org/deck/11936_semantic-data-web-lecture-series
• Introduction to linked data and its lifecycle on the web
• http://euclid-project.eu/
• http://videolectures.net/wims2011_auer_interlinked/
• https://vimeo.com/76257120
• http://www.slideshare.net/slidarko/evolving-the-web-into-a-giant-global-
database-3880018
• http://www.dataversity.net/introduction-to-triplestores/
• http://www.topquadrant.com/2014/05/05/comparing-sparql-with-sql/

An introduction to Linked (Open) Data

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An introduction to Linked (Open) Data