http://schema.org/DataType

In relation to #217 it would seem from the current hierarchy that schema:DataType is the super-class of schema:Boolean, schema:Date, etc.

This would infer that any literal value is a schema:DataType, which seems illogical.

It would seem more logical that:

• the existing datatype classes have type schema:DataType rather than be a sub-class of it
• a top-level class schema:Literal class is introduced (analogous to rdfs:Literal) of which all the existing data types are a sub-class

The result should be something like:

schema:DataType a rdfs:Class ;
  rdfs:subClassOf schema:Class .

schema:Literal a schema:DataType .

schema:Boolean a schema:DataType ;
  rdfs:subClassOf schema:Literal .

schema:Date a schema:DataType ;
  rdfs:subClassOf schema:Literal .