- Resource Description Framework. A very flexible model for data definition organised around triples. These triples forms a directed, labeled graph, where the edges represent the named link between two resources, represented by the graph nodes.
- Simple Knowledge Organization System. An general specification for Knowledge Organisation Systems (thesauri, word lists, authority files, ...) that is commonly serialised as RDF.
- A Uniform Resource Identifier.
- A URN is a specific form of a URI.