internal representation does not distinguish between literal with and without datatype

[satra]

the following are stored internally simply as str, so on re-serialization there is no way to know which to output with or without datatype.

ex:a9 ex:tag1 "hello"^^xsd:string .

and ex:a9 ex:tag1 "hello" .

[stain]

In RDF 1.1 they are equivalent. In fact I think strings should be serialized without explicit ^^xsd:string.

[satra]

@stain - i think part of this is going to be how we check for round trip equivalence. we may have to update both rdflib and prov w.r.t rdf 1.1 equivalence.