[Odrl-version2] RE: ODRL-Version2 Digest, Vol 12, Issue 12

[Vicky Weissman]

Hi Susanne (and everyone else on the list :),

We seem to be talking about adding two types of statements to ODRL.  The
first, which I call prohibitions, says that an action is forbidden if certain
conditions hold.  For example, a prohibition might say "printing is forbidden
if the asset being printed is eArticle #712, the subject doing the printing
is Alice, and Alice has not paid 25 cents".  My guess is that adding
prohibitions to ODRL shouldn't be too hard.  (Note: this is a guess because I
haven't tried to do it.)  

There is another type of statement that you seem interested in, call it an
"all-but" statement.  An all-but statement says that every action but those
in some list A are permitted.  Before we consider how we could add all-but
statements to ODRL, lets think about why/if we really want them.

Possibility 1: the agreement writer wants to use an all-but statement as an
abbreviation for a longer statement.  For example, she might write "permit
all actions but actions a_1,.., a_n" as an abbreviation for "permit actions
a_1',..., a_m' and forbid actions a_1,..., a_n".  Alternatively, "permit all
actions but actions a_1,.., a_n" might be an abbreviation for "permit actions
a_1', ..., a_m'", where m is presumably much larger than n.  Either way, if
all-but statements are simply abbreviations, then I don't think we should add
them to ODRL (since this will make the language longer -> harder to learn).
Instead there should be a program that converts such statements to proper (no
all-but) ODRL. 

Possibility 2: when the agreement writer says "permit all actions but actions
a_1,.., a_n", she really means "forbid actions a_1,..., a_n; I do not object
to any other action being performed".  Suppose this is the case and the
agreement writer later says "forbid action a", where a is not in {a_1, ...,
a_n}.  If the two statements together are not a contradiction, then the
all-but statement is really just a prohibition.  Otherwise, it's another
beast entirely. 

Possibility 3: when the agreement writer says "permit all actions but a_1,..,
a_n", she really means forbid a_1, ..., a_n, and permit every action that is
not in {a_1,..., a_n} - even if that action was not part of the vocabulary
when the agreement was made.

I suspect that the "all-but" statements are either abbreviations, in which
case we shouldn't add them to ODRL, or are prohibitions in disguise, in which
case we can just add prohibitions and be done.  Am I right?  

-Vicky