Differences in current OWL-R DL and OWL-R Full

Hi Boris!

On the last telco, we had this short discussion about to what degree the
current definitions of OWL-R DL and OWL-R Full are aligned. As intended, I
did a few checks afterwards, and here are my results and questions.


(A) Restrictions on class related axioms
----------------------------------------

In OWL R DL, sub class axioms are asymmetrically specified: Not every class
expression, which is allowed on the LHS of a sub class axiom is also allowed
on the RHS, and vice versa. An example is that a unionOf class expression
may only appear on the LHS.  
  
Other examples for class expressions, which are not allowed to appear on
both sides of a sub class axiom are AllValuesFrom, SomeValuesFrom and
(<=1)MaxCardinality.

Other kinds of axioms which are also restricted in their use of certain
class expressions are class equivalence and disjointness axioms, range and
domain axioms, and class assertions.

All these syntactic restrictions do not hold for OWL-R Full. For example,
the following RDF graph is *not* a valid OWL-R DL ontology in RDF graph
form, but it *is* a valid OWL R Full ontology:

  ex:C owl:equivalentClass _:x .
  _:x owl:unionOf ( ex:D1 ex:D2 ) .
  ex:w rdf:type ex:D1
  ex:w rdf:type ex:D2

And this isn't even a particularly strange ontology from a DL point of view,
i.e. it doesn't contain, for example, syntax reflection parts. In fact, it
is a valid OWL 2 DL ontology in RDF graph form. 

Applying the OWL-R (Full) triple rules will result in:

  ex:w rdf:type ex:C

Again, this is not a weird result, but one which one would expect from OWL 2
DL, too. And the entailed triple is of course syntactically valid in OWL-R
DL. 

If the unification process is performed without a change of either the OWL-R
(DL) syntactic restrictions, or the OWL-R (Full) rules, then the set of
OWL-R rules will produce such additional "DL-meaningful looking" results
from "DL-meaningful looking" RDF graphs, which will go beyond the OWL-R
specification.
 

(B) Unrestricted property related axioms
----------------------------------------

In the telco, I specifically asked for sub property chains as an example for
a language feature, which is in OWL-R Full, but not in OWL-R DL. However, I
now see that sub property chains are really included in OWL-R DL. On the one
hand, property expressions are unrestricted:

  4.2.2 Property expressions

  "Property expressions in OWL-R DL are identical to the
  property expressions in OWL 2 [OWL 2 Specification].

And further, property axioms are also unrestricted:

  4.2.5 Axioms

  OWL-R DL redefines all of [OWL 2 Specification] that refer to
ClassExpression.
  [...]
  All other axioms in OWL-R DL are defined as in OWL 2.

But I wonder how this can be the case. Is it really certain that the
unrestricted use of all the property axioms will maintain tractability?
Again, my test case would be sub property chains here.
 
Cheers,
Michael

--
Dipl.-Inform. Michael Schneider
FZI Forschungszentrum Informatik Karlsruhe
Abtl. Information Process Engineering (IPE)
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Fax  : +49-721-9654-727
Email: Michael.Schneider@fzi.de
Web  : http://www.fzi.de/ipe/eng/mitarbeiter.php?id=555

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