[xacml] Which date duration functions mandatory?

We decided not to make date duration functions mandatory for XACML 1.0,
because they can be a bear to get right.

For conformance tests, I am trying to pin down exactly which functions
are "date duration" functions.  The following is my understanding:

Any function that requires converting a value into a new date value is
NOT mandatory.  I.e. "7/24/02 plus 10 days = 8/3/02" is NOT mandatory.

Any function that requires subtracting two date values to obtain a
duration is NOT mandatory.  I.e. "8/3/02 - 7/24/02 = 10 days" is NOT
mandatory.

Any function that adds, subtracts, etc. durations of days, months, or
years to yield a new duration IS mandatory.  I.e. "8 days plus 10 days
= 18 days" IS mandatory.

Anne Anderson       
Internet Security Research Group, Sun Labs
Sun Microsystems, Inc., Burlington, MA