RE: About a more strict definition of Constraint

I don’t see how it is meaningful to constrain either parties or targets. In fact, I think it just introduces problems for evaluating policies.

(What follows is all based on my experience with implementing an engine to evaluate ODRL automatically. And it is the same argument for why I think it is a mistake to indicate any properties of parties other than their URI - such as whether or not they are a “group”).

When you’re evaluating an ODRL policy, you’re trying to determine “Am I permitted to perform this action on this asset?”. More generally, it could be stated as “Is Party P permitted to perform Action A on Asset X?”. That means you need to determine whether various entities in the Policy are “the same as” the entities you’re interested in. Is the Policy Asset “the same as” Asset X and is the Policy Assignee “the same as” Party P? (In fact, it is much more complicated than this, as you also need to determine whether the Policy Action is “the same as” Action A – ODRL actions are hierarchical, so it is quite likely the action you wish to perform is very granular, but the Policy Action could be much more general – an ancestor of Action A in the ODRL tree. And the same thing applies to values for constraints such as location – the Policy may constrain actions in Europe. And you might want to perform the Action in Istanbul or Geneva or London).

So, a lot of the work that an ODRL evaluation engine must perform is to evaluate rules to determine whether various values are “the same as” other values. So, what would it mean to introduce constraints on those values in the Policy itself? How can a Party have both a URI *and* a constraint? What is that meant to mean? I can understand a Party URI which means “people known to be 18 years and older”. But I don’t understand how an engine is meant to evaluate a URI and a constraint – unless we want to introduce rules for how to deal with contradictions between what is stated in the Policy constraints and what is “known” by the evaluating engine.

Regards,

Stuart



From: Renato Iannella [mailto:renato.iannella@monegraph.com]
Sent: Tuesday, November 08, 2016 8:40 AM
To: W3C POE WG
Subject: Re: About a more strict definition of Constraint


I think the general issue is that we have associated the Constraint to the Perm/Prohib/Duty, when we should have associated it directly to the Action/Name.

Michael’s example show that with the “odrl:constraintsubject” having to explicitly refer to the odrl:action.

And this gets worse when we introduce support for Constraints on Asset’s and Parties.

*IF* we move the constraint directly as a property of the Action/Name, then we could express:

  odrl:permission [

    a odrl:Permission ;

    odrl:target <http://example.com/music:4545<http://example.com/music:4545>> ;

    odrl:assigner <http://example.com/sony:10<http://example.com/sony:10>> ;

    odrl:action [

      a odrl:Action ;

      rdf:value odrl:copy ;

      odrl:constraint [

        a odrl:Constraint ;

        odrl:count 1 ;

        odrl:operator odrl:lteq

      ]

    ]

  ] .

This makes the constraint clearly associated with the odrl:copy action (and all constraints in that Action will apply to the same).



Then, when we add a Constraint to the Target, the subject is clear:



 odrl:target [

      a odrl:Asset ;

      rdf:value <http://example.com/music:4545<http://example.com/music:4545>> ;

      odrl:constraint [

        a odrl:Constraint ;

        spotify:artist <http://music.net/people:prince<http://music.net/people:prince>> ;

        odrl:operator odrl:eq

      ]

    ]
And the same for Party:

odrl:assignee [
      a odrl:Party ;
      rdf:value <http://example.com/billie<http://example.com/billie>> ;
      odrl:constraint [
        a odrl:Constraint ;
        spotify:age 18 ;
        odrl:operator odrl:gteq
      ]
    ]

Then we have our favourite example…the constraint on a constraint.
The constraint “end of the football match” is further constrained by a “30 min time period”:

   odrl:action [
      a odrl:Action ;
      rdf:value odrl:distribute ;
      odrl:constraint [
        a odrl:Constraint ;
        odrl:event <http://premier-league.com/end-of-match<http://premier-league.com/end-of-match> ;
        odrl:operator odrl:eq ;
        odrl:constraint [
          a odrl:Constraint ;
          odrl:dateTime "P30M" ;
          odrl:operator odrl:gteq ;
      ]
    ]
  ] .


Renato

ps: i’ve used rdf:value here but we could define our own predicate