A URI reference within an RDF graph (an RDF URI reference) is a Unicode string [UNICODE] that:
- is in Normal Form C [NFC] and
- would produce a valid URI character sequence (per RFC2396 [URI], sections 2.1) when subjected to encoding.
The vocabulary is fully extensible, being based on URIs with optional fragment identifiers (URI references, or URIrefs). URI references are used for naming all kinds of things in RDF.