Combining Algorithms Clarification

Hi all,
I am new to Xacml.It would be helpful if any one can explain ,
 What is the rationality for having Deny-Overrides and Ordered Deny
Overrides Rule/Policy combining algorithm in the xacml
 specification.According to my understanding, the result of both the
algorithms will be the same.Or am I missing something?
 However  one of the implementations like SUN's implementation implements
both algorithms as ordered , so
 there does not seem to be a difference.

Thank You,
Dhivya