Linked Open Data Cloud
The interconnected ecosystem of RDF datasets published according to Berners-Lee's linked-data principles, visualized as the well-known LOD cloud diagram. Strongest in cultural-heritage catalogs, life-science databases, and Wikidata, where institutional payoffs justify the cost of ontology engineering.
The Linked Open Data Cloud (LOD cloud) is the visual and conceptual map of interlinked RDF datasets that have been published on the open web according to the four Linked Data principles articulated by Tim Berners-Lee: use URIs as names for things, use HTTP URIs so they can be looked up, return useful information when looked up, and include links to other URIs. The diagram, maintained by researchers at the University of Mannheim and earlier at the Free University of Berlin, grew from a handful of datasets in 2007 to many hundreds covering geography, government, media, life sciences, libraries, and cross-domain hubs. DBpedia, which extracts structured triples from Wikipedia, served as an early central hub. The LOD cloud's most durable successes have been in cultural heritage (Europeana and national libraries such as the British Library and the National Library of Wales align their catalogs through linked data and increasingly through Wikidata) and in life sciences (UniProt, Bio2RDF, Chem2Bio2RDF, and dozens of other biomedical resources publish their data as queryable RDF). These domains share the property that institutional commitment and integration value justify the ontology work, even as the broader Semantic Web dream of universal machine-readable markup faded on the consumer web.