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

"Peter F. Patel-Schneider" <pfpschneider@gmail.com> wrote on 06/11/2015 
05:15:48 PM:

> Recursions through negations (including XOR, QCRs, etc.) are much 
tougher.
> 
> There has been quite a bit of discussion on this in the working group
> mailing list already.

Yes, I understand. But most people seem to be willing to simply declare 
that one cannot use negation along with recursion.

Are you saying that treating your example from ISSUE-66 as invalid, as 
Holger suggested, is better from that point of view (negation)?
--
Arnaud  Le Hors - Senior Technical Staff Member, Open Web Technologies - 
IBM Software Group

> 
> peter
> 
> 
> On 06/11/2015 04:29 PM, 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)? 
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
> >> 
> >> 
> > 
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