The specification of canonical N-Triples is silent about the datatype of xsd:string literals. More specifically :

    "hello world"

and

   "hello world"^^<http://www.w3.org/2001/XMLSchema#string>

are equivalent terms in N-Triples and N-Quads, and the spec does not say which one should be used as the canonical form.

This has an impact on the RCH working group (w3c/rdf-canon#66).