Linked Data

Linked Data is a sub-topic of the Semantic Web. The term Linked Data is used to describe a method of exposing, sharing, and connecting data via dereferenceable URIs on the Web.

Contents 1 Principles 2 Components 3 Linking Open Data Community Project 3.1 Dataset instance and class relationships 4 Examples 4.1 Datasets 4.2 Use case demos 5 See also 6 External links 6.1 Further reading 6.2 Browsers 6.3 Presentations 6.4 Events

[edit] Principles

Tim Berners-Lee outlined four principles of Linked Data in his Design Issues: Linked Data note, paraphrased along the following lines:

1. Use URIs to identify things.
2. Use HTTP URIs so that these things can be referred to and looked up ("dereferenced") by people and user agents.
3. Provide useful information about the thing when its URI is dereferenced, using standard formats such as RDF/XML.
4. Include links to other, related URIs in the exposed data to improve discovery of other related information on the Web.

Tim Berners-Lee gave a presentation on Linked Data at the TED 2009 conference. In it, he restated the linked data principles as three "extremely simple" rules:

1. All kinds of conceptual things, they have names now that start with HTTP.
2. I get important information back. I will get back some data in a standard format which is kind of useful data that somebody might like to know about that thing, about that event.
3. I get back that information it's not just got somebody's height and weight and when they were born, it's got relationships. And when it has relationships, whenever it expresses a relationship then the other thing that it's related to is given one of those names that starts with HTTP.

Note that although the second rule mentions "standard formats", it does not require any specific standard, such as RDF/XML.

[edit] Components

• URIs (specifically, of the dereferenceable variety)
• HTTP
• Resource Description Framework (RDF)
• Serialization formats (RDFa, RDF/XML, N3, Turtle, and others)

[edit] Linking Open Data Community Project

The goal of the W3C Semantic Web Education and Outreach group's Linking Open Data community project is to extend the Web with a data commons by publishing various open datasets as RDF on the Web and by setting RDF links between data items from different data sources. In October 2007, datasets consisted of over two billion RDF triples, which were interlinked by over two million RDF links. By May 2009 this had grown to 4.2 billion RDF triples, interlinked by around 142 million RDF links. There is also an interactive visualization of the linked data sets to browse through the cloud.

[edit] Dataset instance and class relationships

Clickable diagrams that show the individual datasets and their relationships within the DBpedia-spawned LOD cloud, as shown by the figures to the right, are:

• Instance relationships amongst datasets
• Class relationships amongst datasets

[edit] Examples

[edit] Datasets

• DBpedia - a dataset containing extracted data from Wikipedia; it contains about 2.18 million concepts described by 218 million triples, including abstracts in 11 different languages (see the very DBpedia resource associated to the present wikipedia page)
• DBLP Bibliography - provides bibliographic information about scientific papers; it contains about 800,000 articles, 400,000 authors, and approx. 15 million triples
• GeoNames provides RDF descriptions of more than 6,500,000 geographical features worldwide.
• Revyu - a Review service consumes and publishes Linked Data, primarily from DBpedia.
• riese - serving statistical data about 500 million Europeans (the first linked dataset deployed with XHTML+RDFa)
• UMBEL - a lightweight reference structure of 20,000 subject concept classes and their relationships derived from OpenCyc, which can act as binding classes to external data; also has links to 1.5 million named entities from DBpedia and YAGO
• Sensorpedia - A scientific initiative at Oak Ridge National Laboratory using a RESTful web architecture to link to sensor data and related sensing systems.
• FOAF - a dataset describing persons, their properties and relationships
• OpenPSI for the OpenPSI project a community effort to create UK government linked data service that supports research
• VIAF (Virtual International Authority File) - an aggregation of authority files (author names) from national libraries from around the world.

[edit] Use case demos

• Data from Northwind SQL Schema as Linked Data
• Linked data for the discipline of numismatics

[edit] See also

• Entity-attribute-value model
• Open Data

[edit] External links

[edit] Further reading

• Linked Data Web architecture note by Tim Berners-Lee
• Christian Bizer, Tom Heath, Tim Berners-Lee (2009). Linked Data - The Story So Far. International Journal on Semantic Web and Information Systems (IJSWIS), Vol. 5(3), Pages 1-22. DOI: 10.4018/jswis.2009081901
• Linked Data at the ESW Wiki
• Linking Open Data project wiki home page
• List of public Linked Data sources
• LinkedData.org
• Tutorial: How to publish Linked Data on the Web - Chris Bizer, Richard Cyganiak, Tom Heath
• White Paper: How to publish Linked Data on the Web using OpenLink Virtuoso
• Linked Data on the Web - Chris Bizer, Tom Heath, Kingsley Idehen, Tim Berners-Lee. In Proceedings WWW2008, Beijing, China.
• Interlinking Open Data on the Web - Chris Bizer, Tom Heath, Danny Ayers, Yves Raimond. In Proceedings Poster Track, ESWC2007, Innsbruck, Austria.

[edit] Browsers

• razorbase - Faceted browser for LOD cloud data.
• The Tabulator - Generic data browser and editor.
• OpenLink Data Explorer (ODE)
• Zitgist DataViewer - Linked Data Viewer
• Disco - Hyperdata Browser - A simple browser for navigating the Semantic Web.
• LENA - a Fresnel LEns based RDF/Linked Data NAvigator with SPARQL selector support.
• RelFinder - Visual relationship discovery and exploration.
• Sheaflight - Visual Linked Data Browser.
• VisiNav - Visual Data Navigation.
• Wandora - information mashup creator with numerous information extractors.

[edit] Presentations

• Tim Berners Lee : The next Web of open, linked data at TED
• Linked Data Tutorial - Michael Hausenblas
• Linked Data: Principles and State of the Art - Chris Bizer, Tom Heath, Tim Berners-Lee at WWW2008
• The Linking Open Data Project - Bootstrapping the Web of Data - Tom Heath
• Creating, Deploying and Exploiting Linked Data - Keynote by Kingsley Idehen at Linked Data Planet, 2008
• Deploying Linked Data using OpenLink Virtuoso
• Native to a Web of Data - Tom Coates

[edit] Events

• Workshop on Linked Data on the Web (LDOW2009) at WWW2009
• Workshop on Linked Data on the Web (LDOW2008) at WWW2008
• LinkedData Planet 2008 conference in New York City

v • d • e Semantic Web Background World Wide Web  · Internet  · Hypertext  · Databases  · Semantic networks  · Ontologies Sub-topics Linked Data  · Data Web  · Hyperdata  · Dereferenceable URIs  · Rule bases  · Data Spaces Applications Semantic wiki · Semantic publishing · Semantic search · Semantic computing · Semantic advertising · Semantic reasoner · Semantic matching · Semantic mapper · Semantic broker · Semantic analytics · Semantic service oriented architecture Related topics Folksonomy  · Library 2.0 · Web 2.0  · Open Database Connectivity  · References  · Information architecture  · Knowledge management  · Collective intelligence  · Topic Maps  · Mindmapping  · Metadata · Geotagging · Description logic Standards Syntax & Supporting Technologies : RDF (RDF/XML  · Notation 3  · Turtle  · N-Triples)  · SPARQL  · URI  · HTTP  · XML Schemas, Ontologies & Rules : RDFS  · OWL  · Rule Interchange Format  · Semantic Web Rule Language Semantic Annotation : RDFa  · eRDF  · GRDDL  · Microformats Common Vocabularies : FOAF  · SIOC  · Dublin Core  · SKOS Others: Plain Old Semantic HTML