What is Linked Data ?

In computing, linked data describes a method of publishing structured data so that it can be interlinked and become more useful. It builds upon standard Web technologies such as HTTP, RDF and URIs, but rather than using them to serve web pages for human readers, it extends them to share information in a way that can be read automatically by computers. This enables data from different sources to be connected and queried.
Tim Berners-Lee, director of the World Wide Web Consortium, coined the term in a design note discussing issues around the Semantic Web project. However, the idea is very old and is closely related to concepts including database network models, citations between scholarly articles, and controlled headings in library catalogs.

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 denote 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, leveraging standards such as RDF*, SPARQL.
4. Include links to other related things (using their URIs) when publishing data 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.