In specification of new property (v2r column or m2r mapping relation), allow to indicate whether it's a datatype (literal) or an object (uri) property.
Then adjust cell editing accordingly:
only accept URI if object property
accept string literal for datatype property (more specific type could be handled later)
In specification of new property (v2r column or m2r mapping relation), allow to indicate whether it's a datatype (literal) or an object (uri) property.
Then adjust cell editing accordingly: