The Encoding Scheme entered Dublin Core™ discourse at a 1997 workshop in Canberra, Australia. As originally defined, a Scheme was a Qualifier that "specifie[d] a context for the interpretation of a given element". In 2000, the encoding scheme was differentiated into the Syntax Encoding Scheme and Vocabulary Encoding Scheme.
Note that the word "scheme" is often confused with "schema," which most commonly refers to the specification of a data format (e.g. XML Schema or ShEx Schema); the use of "schema" for an RDF Schema, or vocabulary specification, is somewhat anomalous in this respect.