Linked data

Linked Data is a term used to describe a recommended best practice for exposing, sharing, and connecting pieces of data on the Semantic Web. The practice emphasizes Web access to data using existing Web technologies such as URIs and HTTP. It also emphasizes links between related Web resources.

Principles

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

Use URIs to identify things that you expose to the Web as resources.
Use HTTP URIs so that people can locate and look up (dereference) these things.
Provide useful information about the resource when its URI is dereferenced.
Include links to other, related URIs in the exposed data as a means of improving information discovery on the Web.

Technology Components

Linked Data is made available on the Web using the Resource Description Framework (RDF), a flexible data model for publishing, and integrating heterogeneous data on the Web. RDF model instance data can be serialized in a number of ways en route to publishing data on the web, formats include: XML, Notation 3 (N3), Turtle (terse RDF triple language) and others.

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. As of October 2007, datasets consist of over two billion RDF triples, which are interlinked by over two million RDF links.

Usage Examples

Examples of Linked Data

DBpedia - a dataset containing extracted data from Wikipedia; it contains about 1.6 million concepts described by 91 million triples, including abstracts in 10 different languages
DBLP Bibliography - provides bibliographic information about scientific papers; it contains about 800,000 articles, 400,000 authors, and approx. 15 million triples
Semantic Web School - Vienna: The Semantic Web School provides the latest information on issues about the Semantic Web in form of its d2r mapped press collection with glossary, wikilinks and so forth using the d2r-server and rss features.
GeoNames provides RDF descriptions of more than 6,500,000 geographical features worldwide.

Linked Data (Semantic Web) Browsers and Related

Tabulator
Disco
Openlink RDF Browser
Objectviewer
Ripple, an interactive scripting language
zLinks, a WordPress linked data plug-in.

Software as Service Applications

Revyu - a Review service consumes and publishes Linked Data, primarily from DBpedia, the Linked Data-compatible and Database variant of Wikipedia.
riese - serving statistical data about 500 million Europeans (the first linked dataset deployed with XHTML+RDFa)