Tuesday, January 17, 2012

A First Look at ODRL v2

With other things taking high priority over the last 6 months, this is the first opportunity I’ve had to look at the progression of ODRL Version 2.0, and evaluating where it’s improved from the earlier versions. 

First things first, ODRL has migrated to the W3C as a Community Working Group.  Overall, this is a good thing.  It opens it up to the wider W3C community, gives greater credence to the effort and more importantly, more exposure.  Well done. 

On to my first impressions:

1 . The model has been greatly simplified.   With ODRL 1.x, it was possible to express the same rights statement in several different ways.  The obvious implication was that it was virtually impossible to build a generalized API for processing IP Rights, save running XJC on the schema, which isn't necessarily always what I want.  It wasn’t all bad news though, the 1.x extension model was extremely flexible and enabled the model to support additional business-specific rights logic.  

2. Flexible Semantic Model.  The 2.0 model has a strong RDF-like flavor to it.  Essentially, all of the entities, assets, parties (e.g., rightsholders, licensees), permissions, prohibitions, and constraints are principally URI-based resource pointers that imply semantics to each of the entities.  Compared to 1.x, this is a vast improvement to its tag-based semantics, which meant that you were invariably extending either the ODRL content model, data dictionary, or both.
3. Needs More Extensibility.   The current normative schema, still in draft, does need some additional design.  Out of the box testing with Oxygen shows that only one element is exposed (policy).  All of the other element definitions are embedded within the complexType models, which means makes it difficult to extend the model with additional structural semantics.  This is extremely important on a number of fronts:
  • The current model exposes assets as explicit members of a permission or prohibition.  Each “term” (i.e., permission or prohibition) is defined by an explicit action (print, modify, sell, display).  It’s not uncommon to have a policy that covers dozens or hundreds of assets.   So for each term, I have to explicitly call out each asset.  This seems a little redundant.  The 1.x model had the notion of terms that applied to all declared assets at the beginning of the policy (or in the 1.x semantics, rights).  I’d like to see this brought back into the 2.0 model.
  • The constraint model is too flat.  The new model is effectively a tuple of: constraintName, operator, operand.  This works well for simple constraints like the following psuedo-code : “print”, “less than”, “20000”, but doesn’t work well for situations where exceptions may occur (e.g., I have exclusive rights to use the asset in the United States until 2014, except in the UK; or I have worldwide rights to use the asset in print, except for North Korea, and the Middle East).   Instead, I have to declare the same constraint twice:  once within a permission, and second time as a prohibition.   I’d like the option to extend the constraint model to enable more complex expressions like the ones above.

    Additionally list values within constraints are expressed tokenized strings within the rightOperand attribute.  While completely valid to store values in this, I have a nit against these types of token lists, especially if the set of values is particularly long, like it can for things like countries using ISO-3166 codes. 
I shouldn’t have to extend the whole complexType declaration in order to extend the model with my own semantics. However the current schema is structured that way.   Instead, I’d like to see each entity type exposed as an “abstract” element, bound to a type, which ensures that my extension elements would have to at least conform to the base model. 


I’m looking forward to using this with our Rights Management platform.  The model is simple and clean and has a robust semantics strategy modeled on an RDF-like approach.  This will make it easier to use the out-of-the-box model.  That said, it’s missing some key structures that would make it easier to use and extend if I have to, but that can be address with a few modifications to the schema.  (I have taken a stab at refactoring to test this theory – it’s pretty clean and I’m able to add my “wish list” extensions with very little effort.

Link: http://dl.dropbox.com/u/29013483/odrl-v2-proposed.xsd

No comments: