RDF: a fact as a triple with a global address
On 22 February 1999 the W3C made the RDF specification a Recommendation. It set one way to write a statement about any web resource: subject, predicate, object, with subject and predicate named by a URI.
Why it matters
Until then every knowledge base had its own names for its own concepts, and merging two meant agreeing on a vocabulary first. RDF made the name of a concept a web address, so two graphs built independently can be laid side by side and seen to speak about the same thing. That is the condition without which the later open fact bases could not have pointed at each other.
The editors were Ora Lassila of Nokia Research Center and Ralph R. Swick of the W3C. The document explains the triple on its own example: the sentence "Ora Lassila is the creator of the resource http://www.w3.org/Home/Lassila" decomposes into a subject (the resource), a predicate (Creator) and an object (the literal "Ora Lassila"). It is drawn, in the text's words, using "directed labeled graphs (also called 'nodes and arcs diagrams')". What this record does not claim. The 1999 document defines neither an inference logic nor a vocabulary of classes: RDF Schema was separate work, and an ontology language arrived only five years later. Nor does it claim that XML was the only permitted writing: the specification gives a serialization syntax in XML and an abbreviated form of the same, and the abstract model was separated from the syntax only in the 2004 revision.