RDF (Resource Description Framework)

The W3C standard graph data model under the semantic web — the base layer of knowledge-representation. Everything is a triple: a subject (a resource, named by a URI/IRI or a blank node), a predicate (a URI naming a relationship/property), and an object (a URI, blank node, or literal). Many triples form a directed graph, which models flexible, schema-optional data better than rigid relational tables.

Abstract model, many serializations

RDF is an abstract model; its concrete syntaxes are interchangeable skins over the same graph: Turtle (the compact, human-friendly default), JSON-LD (the JSON form, and the one that won on the web), RDF/XML (the historical syntax — “RDF ≠ RDF/XML” is a standing correction; some graphs can’t even be expressed in RDF/XML due to XML QName limits), N-Triples/N-Quads, TriG, Notation3.

A subtle but load-bearing point: a URI that names a resource need not be dereferenceable. http: identifiers are unique names, not necessarily fetchable addresses — which is what lets RDF describe physical objects and abstract concepts, not just web documents.

Where it sits in the stack

RDF is the floor; the rest of the knowledge-representation stack builds up from it: RDFS → OWL (classes, hierarchies, reasoning), SHACL (validation/shapes), and SPARQL (the query language). Real deployments on top include Wikidata and DBpedia (RDF knowledge bases), FOAF, Creative Commons license metadata, and — pulling RDF onto the mainstream web — schema-org.

History & status

First W3C recommendation 1999; RDF 1.0 (2004), RDF 1.1 (2014, current — the URI→IRI shift came here). Lineage from PICS, Dublin Core, and Guha & Bray’s Meta Content Framework.

Criticisms

The documented knocks are about cost, not capability: verbosity / URI wordiness, a steep learning curve, and the RDF/XML representation gaps. These feed the spoke’s central vision-vs-deployment tension (synthesis): the formal model is powerful but heavy, which is why the lightweight schema-org slice is what scaled.

Tier

T2 — Wikipedia, an authoritative encyclopedic overview of a W3C standard (tertiary; the W3C specs themselves are the T1 to fold in later if we go deeper on a specific layer).

knowledge-representation · schema-org · ontology-dev-tools · knowledge-graph · synthesis