outlined four principles of linked data in his "Linked Data" note of 2006, paraphrased along the following lines: 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:
Linked open data is linked data that is open data. Tim Berners-Lee gives the clearest definition of linked open data in differentiation with linked data. Large linked open data sets include DBpedia and Wikidata.
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 September 2011 this had grown to 31 billion RDF triples, interlinked by around 504 million RDF links. A detailed statistical breakdown was published in 2014.
There are a number of European Union projects involving linked data. These include the linked open data around the clock project, the PlanetData project, the DaPaaS project, and the Linked Open Data 2 project. Data linking is one of the main goals of the EU Open Data Portal, which makes available thousands of datasets for anyone to reuse and link.
are formal descriptions of data structures. Some of the better known ontologies are:
FOAF – an ontology describing persons, their properties and relationships
UMBEL – a lightweight reference structure of 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
DBpedia – a dataset containing extracted data from Wikipedia; it contains about 3.4 million concepts described by 1 billion triples, including abstracts in 11 different languages
GeoNames – provides RDF descriptions of more than geographical features worldwide.
Global Research Identifier Database – an international database of institutions engaged in academic research, with relationships, models two types of relationships: a parent-child relationship that defines a subordinate association, and a related relationship that describes other associations
Dataset instance and class relationships
Clickable diagrams that show the individual datasets and their relationships within the DBpedia-spawned LOD cloud are available.