[Odrl-version2] Permissions and Prohibitions

[Renato Iannella]

Dear all - an issue for discussion on if Permissions and Prohibitions
can occur together (see the early model [1]) in the same expression.

A1) Permissions indicate the actions you are allowed to do *and* only 
these actions
B1) Prohibitions indicate the actions you are not allowed to do *but* 
everything else is OK

If A1 and B1 are mutually exclusive, then it is OK.
However, if you put them together in an expression, you need to refine 
the rules, like:

A2) Permissions indicate the actions you are allowed to do
B2) Prohibitions indicate the actions you are not allowed to do
C) If A2 occurs and no B2, then you can only do A2
D) If B2 occurs and no A2, then you can do anything except B2
E) If A2 and B2 occurs, you can only do A2 and not B2

(Rule E is a bit redundant in that if you can only do A2, then that 
also means
you can't do B2)

An example of where Permissions and Prohibitions may be used together 
is in
the Creative Commons licenses. (In the ODRL CC Profile [2], we have 
turned
CC Prohibitions into negative Constraints.)

The issue is do we keep the Permissions and Prohibitions as mutually 
exclusive
or we have some refined rules and allow them both to appear in the same 
expression.

Cheers

Renato Iannella
ODRL Initiative
http://odrl.net

[1] <http://odrl.net/2.0/images/odrl-V2-model-draft3.png>
[2] <http://odrl.net/Profiles/CC/WD.html>