Re: ISSUE-22: Proposal based on sh:hasShape

On 6/12/2015 9:29, Arnaud Le Hors wrote:
> Holger Knublauch <holger@topquadrant.com> wrote on 06/10/2015 06:11:24 PM:
>
> > From: Holger Knublauch <holger@topquadrant.com>
> > To: RDF Data Shapes Working Group <public-data-shapes-wg@w3.org>
> > Date: 06/10/2015 06:13 PM
> > Subject: ISSUE-22: Proposal based on sh:hasShape
> >
> > I would like to write down the solution to the recursion issue that I
> > have currently implemented in my prototype, and welcome comments 
> whether
> > this would resolve the issue.
> >
> > Recursive evaluation of shapes can only be triggered via the 
> sh:hasShape
> > function. sh:hasShape takes three arguments:
> >
> >      sh:hasShape(?focusNode, ?shape, ?shapesGraph)
> >
> > Proposal: sh:hasShape must fail with a constraint violation, if it
> > encounters a recursive call involving the same combination of 
> arguments.
>
> I'd like to know what makes you choose to declare this a failure. 
> Couldn't we just as well decide that in this case the recursion stops 
> there assuming the constraint is satisfied (for the next iteration)?

Yes, perhaps. Indeed I have this implemented too, and it seems to also 
work OK for the Italian family test case. The main reason why I chose 
the failure was to be extra-safe without getting too deep into the 
theoretical implications. I am not the best person to ask whether the 
other solution would work in theory - we have better firepower on these 
topics in the WG ;)

Holger


> This would mean that Peter's example in ISSUE-66 would be valid:
>
> ex:i rdf:type ex:C .
> ex:i ex:p ex:i .
>
> with the shape
>
> exs:S rdf:type sh:Shape;
> sh:classScope ex:C ;
> sh:property [ sh:predicate ex:p ;
> sh:minCount 1 ; sh:maxCount 1 ;
> sh:valueShape exs:S ] .
>
> As a user this seems quite natural to me but maybe there are other 
> examples for which this wouldn't be the case. I don't know.
> --
> Arnaud  Le Hors - Senior Technical Staff Member, Open Web Technologies 
> - IBM Software Group
>
> > The constraint violation could have a system generated message such as
> > "Failed to evaluate constraint due to unsupported recursive use of
> > sh:hasShape" and point at the focus node that was visited twice.
> >
> > This would still allow most interesting cases that involve recursion
> > between shapes, but excludes cases where the same instances are visited
> > more than once.
> >
> > What am I missing?
> >
> > Thanks,
> > Holger
> >
> >
>