Thursday, July 2, 2009

What is the LOD cloud?

LOD is an acronym for Linking Open Data, although sometimes in is less correctly referred to as Linked Open Data. A set of principles for Linked Data were espoused by Tim Berners-Lee. Unlike the traditional Web which consists of hyperlinked HTML Web pages, Linked Data consists of hyperlinked data in the form of RDF triples. Technically, cloud usually refers to a network of servers, but sometimes it is used to refer to interconnected data, essentially a synonym for Web. The LOD cloud, or Linking Open Data cloud, is the current totality of the interconnected data produced by the Open Data Movement in the form of the W3C SWEO Linking Open Data community project. SWEO refers to the W3C Semantic Web Education and Outreach Interest Group.

The LOD cloud is essentially the rudimentary beginning of the Web of Data or Semantic Web as envisioned by Tim Berners-Lee.

The LOD cloud is also referred to as a data commons. The intention is that all of the data in the LOD cloud is open and freely available. Usually "open" will mean that at a minimum the data is at least accessible. It is also usually expected that the data can be freely copied, but that may not always be the case, depending on the license for a particular subset (data set) for a particular source or supplier. The ultimate sense of openness is that the data may be freely edited by users, but that frequently is not the case, especially for proprietary data or data from a government agency which controls the data. It may be more appropriate to refer to the entire cloud as the Linked Data cloud, and the more open subset as the LOD cloud (Linked Open Data cloud), but such fine distinctions are generally currently not drawn.

The LOD cloud is sometimes referred to as the LOD data cloud, but clearly that is redundant (Linking Open Data data cloud.)

The term LOD dataset (or LOD data set) is sometimes used to refer a well-defined subset of the LOD cloud, such as the data for a specific application or domain or data source. The term LOD datasets or (LOD data sets) refers to some collection of specific LOD data sets, or possibly even all of the datasets in the cloud. The SWEO wiki maintains a list of the known data sets in the LOD cloud.

The concept of data being published to the LOD cloud or the Web is also known as Linked Data on the Web (LDOW) or sometimes even the Semantic Web on the Web.

Another term sometimes used for the LOD cloud is Web of Linked Data.

The term Linked Data Cloud is also sometimes used for the LOD cloud.

The term Linking Open Data on the Semantic Web is sometimes used to refer to the LOD cloud.

Sometimes the term LOD cloud is simply used to refer to the "cloud" diagram or bubble diagram that shows all of the known data sets in the LOD cloud.

For most all intents and purposes, the LOD cloud is the Semantic Web or the Web of Data.

-- Jack Krupansky

2 Comments:

At July 2, 2009 at 5:52 PM , Anonymous Kingsley Idehen said...

There are live LOD cloud caches at:

1. http://lod2.openlinksw.com -- latest
2. http://lod.openlinksw.com -- original

Both of the above provide powerful lookup services. Remember, databases are about the power of lookups and joins, and these servers facilitate both re. the burgeoning "Web of Linked Data" :-)

 
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