[Odrl-version2] RE: ODRL-Version2 Digest, Vol 13, Issue 6

[Vicky Weissman]

<RI>
The question is: are all Permissions valid Duties (and vice-versa) ??
<VW>
According to the May 16 2005 draft of the model semantics, a Permission is a
tuple (act, target, cons, dut), where act is an action, target is an asset,
cons is a possibly empty set of constraints, and dut is a possibly empty set
of duties.  A Duty is either a tuple (act, obj, cons, rel) or a tuple (act,
obj, cons), where act is an action, obj is either an asset or a list of
names, cons is a possibly empty set of constraints, and rel is a Boolean flag
indicating that the duty can be fulfilled at any time (and hence is no duty
at all?). 

Given the definitions, I'm not sure any permission is a valid duty (or
vice-versa).  If we assume that a permission/duty can omit elements if they
are the emptyset, then there's overlap (e.g., permissions of the form (act,
target) are also duties).  Nevertheless, every permission that includes a
non-empty set of duties is not a duty.  Every duty that includes the optional
rel flag is not a permission.      

I'm pretty sure that I've misunderstood your question.  ....  Are you asking
if there is an action that can appear as the first element of a permission
and not as the first element of a duty (or vice-versa)?  If so, then I guess
the answer is that they're your definitions, so you can do whatever you want.
But I don't see any reason why we would want to build such restrictions into
ODRL.  Moreover, having an action that can appear only in a duty seems a bit
odd since it suggests an individual can be obligated to perform an action act
on an object and cannot get (explicit) permission to do act.    

I get the feeling I'm missing the big picture.  Would welcome a clue.

Best,
Vicky