The (first) “RDF Model and Syntax” recommendation (seehttps://www.w3.org/TR/1999/REC-rdf-syntax-19990222/) did not require any form of (external) “schema” or “ontology” to refer to….
It simply allowed RDF statements to be asserted:
<?xml version="1.0"?>
<rdf:RDF
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:s="http://description.org/schema/">
<rdf:Description about="http://www.w3.org/Home/Lassila">
<s:Creator>Ora Lassila</s:Creator>
</rdf:Description>
</rdf:RDF>As long as unique identifiers (namespaces) are used….