Why are PolicySetIdReference and PolicyIdReference distinct elements?

[Danny Thorpe <danny.thorpe@bitkoo.com>]

I was digging through some old code recently and was reminded of a little puzzle I came across some time ago:

 

Why does XACML have different elements for PolicySetIdReference and PolicyIdReference?  They have the same data, same ancestor, and live in the same scope. The only difference is in what lives at the other end of the reference.

 

Are they separate elements to appease a schema requirement?

 

It just seems odd that to identify a policy you have to carry around its unique ID *and* its type. If the ID is truly unique, isn’t the type redundant? 

 

-Danny