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

Hi Michael,

As I was explaining in my earlier emails, the suggested syntax  
specification for OWL-R does not restrict the applicability of the  
rules, it only provides a sufficiency condition for the semantic  
guarantees currently described in Section 4.4 of the current Profiles  
document; i.e., if an RDF graph satisfies the syntactic condition,  
then the semantic guarantees hold. For graphs outside this set, the  
rules will still derive many useful consequences.

It is easy to see that deriving *all* the consequences of the  
equivalentClass axiom you describe would *in general* require non- 
deterministic reasoning of a kind that implementations based on the  
OWL-R rules will not provide. This kind of reasoning would obviously  
cause an undesired increase in worst case complexity.


Regarding your second point, the reason for the relatively low  
complexity of reasoning with ontologies that satisfy the syntactic  
conditions is, intuitively, that they have a single canonical model  
whose domain of interpretation consists exactly of those individuals  
occurring in the ontology. The property axioms can thus be treated  
simply as a set of rules that add implicit property assertions  
(triples) -- which is exactly how they are implemented in the rule  
set (See Table 4).

Regards,
Ian



On 19 Jul 2008, at 16:12, Michael Schneider wrote:

> 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)
> Tel  : +49-721-9654-726
> Fax  : +49-721-9654-727
> Email: Michael.Schneider@fzi.de
> Web  : http://www.fzi.de/ipe/eng/mitarbeiter.php?id=555
>
> FZI Forschungszentrum Informatik an der Universität Karlsruhe
> Haid-und-Neu-Str. 10-14, D-76131 Karlsruhe
> Tel.: +49-721-9654-0, Fax: +49-721-9654-959
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> Studer
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>

Received on Monday, 21 July 2008 09:30:13 UTC