% note with comments on OWL 2 RL Profile, public draft of 2009-04-21
% by Benjamin Grosof, May 12, 2009

Hi Boris, Ian, Zhe, and other OWL 2 Working Group folks,

It's with pleasure (but in a bit of a rush) that I have just read the
OWL 2 RL Profile document, public draft of 2009-04-21 [1], in response
to Ivan Herman's recent personal request that I review it as part of the
2nd Last Call process.

[1] http://www.w3.org/TR/owl2-profiles/  -> #OWL_2_RL (i.e., section 4)

Overall, the document looks like a quite good job.
Below are my suggestion comments on it.  No show stoppers.  But imho they
will help make the document stronger and the adoption a bit easier on
implementers and users.  They are given in descending order of importance. 

Note these comments are by myself as an individual, and do not
represent the views nor position of Vulcan Inc.

I've attached this email as a plaintext file, too, for your convenience.  

Best,
Benjamin 


1. In section 4.3 (Reasoning in OWL RL ...), towards the end, it would
be good to have a brief discussion about how the direct semantics of
most existing implemented rule systems is based on (either rigorously,
or in reasonably close hailing distance to) declarative logic programs
(LP) rather than FOL, and then point to reference work describing the
relationship of LP semantics to FOL semantics.

2. A lesson learned from the experience of OWL 1 is that it would be
useful to have some kind of communal mechanism, ideally under the
auspices of W3C, to recognize and name useful subsets of
expressiveness other than the ones specified as part of the
Recommendation itself (-DL, the Profiles, etc.), that emerge as well
understood and useful only after the Recommendation.  E.g., expressive
relaxations that preserve desired characteristics.  E.g., expressive
restrictions that improve computational performance or improve
simplicity of implementation.  While not absolutely necessary for the
Working Group to do it at this point, it would smooth the way.  Let's
learn from history, folks!

3. Ideally, there would be another document in the OWL 2 document
suite, aimed at implementers as an audience, that acts as a primer on
the implementation *design* considerations and techniques, including
specifically for the RL Profile.  I didn't find anything like this.
(The Conformance document focuses on *test*, as opposed to design.)

4. In section 4.3, theorem PR1:  The proof of this central result
should be more than a short sketch, i.e., should be elaborated.  This
could be via pointer to a separate reference document.

5. In section 4.2 (Profile Specification):  Why are the following three
expressive restrictions imposed?  Please explain. (Or perhaps
generalize if the restrictions can indeed be relaxed.)

  a. No reflexive object property axioms (ReflexiveObjectProperty). Why?

  b. No self property restriction (ObjectHasSelf) in class expressions.  Why?

  c. Data range expressions (DataRange) may only be formed by intersection 
     (DataIntersectionOf).  Why?  In particular, why not permit a data
     range formed by union (DataUnionOf or DataOneOf) in a 
     DataSomeValuesFrom within a subClassExpression?