Re: issue in OWL SS&FS and bug in mapping from RDF graphs

This construct with repeated classes is valid surface syntax, and the wording in 9.13 says that its meaning is to make ex:foo empty.   At the very least there needs to be an erratum to adjusting the wording in 9.1.3 and other places with the same issue.

peter

On Apr 11, 2014, at 3:12 PM, Boris Motik <boris.motik@cs.ox.ac.uk> wrote:

> Hello,
> 
> Since the spec ways that the DisjoinedClasses takes a set of classes as arguments, then stating DisjointClasses( ex:foo ex:foo ex:bar ) is actually impossible  that is, that axiom is not a structurally valid OWL 2 DL axiom. Hence, there is no need to require the arguments in the structural spec to be different. The only thing we could do is maybe clarify the syntax and say that DisjointClasses( ex:foo ex:foo ex:bar ) is then syntactically incorrect. That would obviate the need for 2/ since an RDF graph containing a DisjointClasses axiom with structurally equivalent classes would also be syntactically incorrect.
> 
> Regards,
> 
> Boris
> 
> On 11 Apr 2014, at 22:09, Patel-Schneider, Peter <Peter.Patel-Schneider@nuance.com> wrote:
> 
>> The OWL Structural Specification and Function-Style Syntax states for most syntactic constructs with an arbitrary number of arguments that these arguments are considered to be a set under structural similarity.
>> 
>> This causes no problems for many of these syntactic constructs but there are a few where removing duplicates changes the meaning of the construct.
>> 
>> For example, according to the wording in section 9.1.3 of SS&FS
>> 
>> DisjointClasses( ex:foo ex:foo ex:bar )
>> 
>> implies that ex:foo is empty, which is very different from 
>> 
>> DisjointClasses( ex:foo ex:bar )
>> 
>> It would not be easy to simply change these constructs to take multisets because the OWL API would have to be changed.
>> 
>> 
>> I propose the following fix:
>> 
>> 1/ The functional-style syntax requires that the arguments to DisjointClasses, DisjointObjectProperties, DisjointDataProperties, and DifferentIndividuals and all but the first argument to DisjointUnion all be structurally different.
>> 
>> 2/ When converting the triple x owl:disjointWith y where x and y are structurally similar the axiom SubClassOf( CE(x) owl:Nothing ) is produced.
>> 
>> 
>> This is not an ideal fix by any means, but a better fix would require much more significant changes in deployed software.
>> 
>> 
>> Peter F. Patel-Schneider
>> 
> 

Received on Saturday, 12 April 2014 18:10:08 UTC