XMI21 — More type safety in generated schemas

Document refs are against formal/03-05-02.

According to rule 4d of the Schema production rules on page 2-5,
"The type is 'xsd:string' for simple attributes".

I assume here that "simple attributes" refers to MOF primitive
types (Boolean, Integer, Long, Float, Double, String).

I wonder why xsd:string was used for all these primitive types,
when perfectly suitable data types are predefined for XML Schemas:
there's xsd:boolean, xsd:int, xsd:long, xsd:float and xsd:double
that exactly match the data types used by MOF.

I propose to make use of these existing types to strengthen the
generated schema.