Linked Data

Thanks ReadWriteWeb for this latest on where the web is heading... a useful universe of open, linked data sets. Enjoy

Written by Richard MacManus / May 18, 2009 3:15 AM / 12 Comments

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Last week we discussed how the current era of the Web is evolving. One of the concepts we noted was Linked Data, an idea whose time has come in 2009. Sir Tim Berners-Lee, the inventor of the Web, gave a must-view talk at the TED Conference earlier this year, evangelizing Linked Data. He said that Linked Data was a sea change akin to the invention of the WWW itself. We've gone from a Web of documents, via the WWW, to a Web of data. Berners-Lee is now on a crusade for everyone from government departments, to individuals, to open up their data and put it on the Web - so that others can link to it and use it. In this post we give a high-level overview of Linked Data. Read on to stop and smell the roses.

A great place to start to understand Linked Data is Sir Tim's TED talk, embedded below. It's just over 15 minutes and highly recommended if you want to grok where the Web is headed. The slides are also available.

Linked Data: An Idea Whose Time Has Come

Linked Data is an official W3C project. An independent community page for Linked Data describes it as "using the Web to connect related data that wasn't previously linked, or using the Web to lower the barriers to linking data currently linked using other methods."

Tim Berners-Lee described Linked Data as a grassroots movement in his TED presentation. The above image shows you how many participating data sets there are now (it'll have increased even more since then, as that was a March 2009 snapshot). Linked Data is ramping up fast. To give you an idea of how much it's grown over the past two years alone, here is a snapshot of the data sets that were available in May 2007:

Linked Data in a Nutshell

In a W3C memo that Berners-Lee published in July 2007, he described four principles of Linked Data. The Wikipedia paraphrased it as follows:

• 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.

Even that paraphrasing is a bit technical, but we can sum it up like so: Linked Data allows you to discover, connect to, describe, and re-use all kinds of data. It is to data what the World Wide Web was to documents back in the 90's.

W3C: Linked Data: Principles and State of the Art, April 2008

On ReadWriteWeb we've discussed Linked Data a number of times. Alexander Korth wrote a good high level intro last month. He noted that Linked Data builds on and interconnects existing ontologies such as WordNet, FOAF, and SKOS. He went on to explain that the data sets grant access to their knowledge bases and link to items in other data sets:

"The project follows basic design principles of the World Wide Web: simplicity, tolerance, modular design, and decentralization. The LOD [Linking Open Data] project currently counts more than 2 billion RDF triples, which is a lot of knowledge. (A triple is a piece of information that consists of a subject, predicate, and object to express a particular subject's property or relationship to another subject.) Also, the number of participating data sets is rapidly growing. The data sets currently can be accessed in heterogeneous ways; for example, through a semantic web browser or by being crawled by a semantic search engine."

Let A Thousand Flowers Bloom

If there's one idea we want to leave you with about Linked Data, it's that the data is there to be used. Linked Data enables data to be opened up and connected so that people can build interesting new things from it. At TED, Berners-Lee described Linked Data as boxes of data that - when connected via open standards - enable things to sprout from it.

Slide from Tim Berners-Lee's TED talk in Feb 09

Linked Data is one of the most important trends of the Web circa 2009 and we'll be blogging more about it in the coming months. Let us know in the comments if there's something specific you'd like us to explore in the Linked Data world.