Modification to Base Data Schema Spec

Hi,
I made some modifications this document. In particular since creating the
P3P ontology, I realized that the BDS is not actually a class hierarchy - so
I have included this sentence to describe what it actually is:

Datatype sub-elements are organized into a class-like hierarchy of
increasing specificity. For an element b to be definied as an allowed child
of element a signifies that if an entity is stated to collect data of type
a, then it may also collect data of type b. The inverse relation however
does not hold. Transitivity also holds for this relation. That is, if  a
statement states that entity x may collect data of type a and b is an
allowed structure of a and c is an allowed structure of b, then it can be
assumed that x may collect data of type c. 

Giles