RDF Resource Description Framework
The W3C's data model for the semantic web: everything is expressed as triples of subject, predicate and object.
<Sweden> <capital> <Stockholm>. Out of an ocean of such triples a graph falls out. Identifiers are URIs, which lets data from different sources merge without anyone agreeing on a schema first.
Serialised as Turtle, JSON-LD or (historically) RDF/XML. The grand semantic web never arrived, but RDF lives on in Wikidata, library and pharmaceutical data, and as JSON-LD in Schema.org markup.