[xacml-comment] map function

I'm a little concerned with the definition of the map function. Every other
function and attribute in the spec has a well defined type associated with
it, but the map function does not. Even things like the bag functions are
defined as type-* so that each of the bag functions returns a well defined
type (ie, there is a uniquely named function for each bag function that returns
each attribute type). The map function, however, is simply defined as
returning a bag of some type.

For consistency, and to make sure that the strong typing present in the rest
of the spec exists here too, I would suggest that the map function be
redefined as type-map, such that there is a named map function for each type
in the spec. I think the functionality being provided by map makes sense,
I just think it should be clear what types of bags the map function returns.


seth