Notice that Literal does not include the outer literal/1 predicate. This means that instantiations of Literal cannot be used directly in other rdf_db
predicates.
Literal can have either of the following forms:
type(DatatypeIri,LexicalExpression)
for typed literalslang(LanguageTag,LexicalExpression)
for language-tagged strings- LexicalExpression for plain strings
The predicate rdf_literal/1 in library(semweb/rdf11)
does bind Literal to full literal terms.